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| committer | Roger Frank <rfrank@pglaf.org> | 2025-10-14 20:04:59 -0700 |
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diff --git a/36036-h/36036-h.htm b/36036-h/36036-h.htm new file mode 100644 index 0000000..25633e1 --- /dev/null +++ b/36036-h/36036-h.htm @@ -0,0 +1,4091 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> + <head> + <meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1"> + <meta http-equiv="Content-Style-Type" content="text/css"> + <title> + The Project Gutenberg eBook of Metabolic Adaptation to Climate and Distribution of the Raccoon Procyon Lotor and other Procyonidae, by John N. Mugaas, John Seidensticker, and Kathleen P. Mahlke-Johnson. + </title> + <style type="text/css"> + + body {margin-left: 10%; margin-right: 10%;} + p {text-align: justify; text-indent: 1.5em;} + sub, sup {font-size: 0.8em;} + hr {width: 100%; color: #000; clear: both;} + table {margin-left: auto; padding:4px; margin-right: auto; border-collapse: collapse;} + .noidt {text-align: justify; text-indent: 0em;} + .bb {border-bottom: solid #000 1px;} + .bl {border-left: solid #000 1px;} + .bt {border-top: solid #000 1px;} + .br {border-right: solid #000 1px;} + .blockquot {text-align: justify; margin-left: 10%; margin-right: 10%;} + .pagenum {position: absolute; left: 92%; text-indent:0; font-size: 0.75em; text-align: right; color: #b0b0b0;} + .reference {margin-top: 0.2em; margin-left: 5.5em; text-indent: -3em;} + .vtop {vertical-align: top;} + .vtop2 {position: relative; top: -0.8em;} + .center {text-align: center;} + .justify {text-align: justify;} + .nobreak {white-space:nowrap;} + .text_lf {text-align: left;} + .text_rt {text-align: right;} + .smaller {font-size: 0.8em;} + .smcap {font-variant: small-caps;} + .gesperrt {letter-spacing: 0.1em;} + .caption1 {font-weight: bold; font-size:2.0em; text-align: center; margin-top: 3em; margin-bottom: 2em;} + .caption2 {font-weight: bold; font-size:1.50em; text-align: center; margin-top: 2.5em; margin-bottom: 1em;} + .caption3 {font-weight: bold; font-size:1.25em; font-variant: small-caps; text-align: center; margin-top: 2em; margin-bottom: 1em;} + .caption4 {font-weight: bold; font-size:1.15em; font-style: italic; text-align: center; margin-top: 1.75em; margin-bottom: 1em;} + .trans_notes {background:#d0d0d0; padding: 7px; border:solid black 1px;} + .pub_list td {vertical-align: top;} + .tab_cap {font-weight: bold; margin-right: 5%; margin-left: 5%; text-align: justify; margin-top: 3em;} + .fig_cap {font-weight: bold; margin-right: 5%; margin-left: 5%; text-align: justify; margin-bottom: 3em;} + .ind2em {text-indent:2em;} + .m_left5 {margin-left: 5em;} + .footnote {margin-left: 10%; margin-right: 10%; font-size: 0.9em;} + .footnote .label {position: absolute; right: 84%; text-align: right;} + .fnanchor {vertical-align: super; font-size: .8em; text-decoration: none;} + .dot {font-weight: bold; position: relative; top: -12px; left: 8px; z-index: 2;} + .V {position: relative; z-index: 1;} + .sup2 {position: relative; top: -6px;} + + </style> + </head> +<body> + + +<pre> + +The Project Gutenberg EBook of Metabolic Adaptation to Climate and +Distribution of the Raccoon Procyon Lotor and Other Procyonidae, by John N. Mugaas and John Seidensticker and Kathleen P. Mahlke-Johnson + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Metabolic Adaptation to Climate and Distribution of the Raccoon Procyon Lotor and Other Procyonidae + +Author: John N. Mugaas + John Seidensticker + Kathleen P. Mahlke-Johnson + +Release Date: May 5, 2011 [EBook #36036] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK THE RACCOON PROCYON LOTOR *** + + + + +Produced by Colin Bell, Tom Cosmas, Joseph Cooper and the +Online Distributed Proofreading Team at http://www.pgdp.net + + + + + + +</pre> + + + + + + +<p><span class="pagenum"><a name="Cover" id="Cover">[Cover]</a></span></p> +<br> +<div class="center"> + <img src="images/cover.png" width="448" height="570" title="cover" alt="cover"> +</div> +<br> +<br> +<br> + +<p><span class="pagenum"><a name="Page_i" id="Page_i">[Pg i]</a></span></p> + +<div class="caption3 gesperrt">SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY · NUMBER 542</div> + +<div class="caption1">Metabolic Adaptation to Climate<br> +and Distribution of the Raccoon<br> +<i>Procyon lotor</i> and Other Procyonidae</div> + +<div class="caption2"><i>John N. Mugaas, John Seidensticker,<br> +and Kathleen P. Mahlke-Johnson</i></div> + +<div class="center"> +<img src="images/smithsonian_logo.png" width="92" height="87" title="" alt=""> +<br> + +SMITHSONIAN INSTITUTION PRESS<br> +Washington, D.C.<br> +1993 +</div> + + +<br> +<br> +<p><span class="pagenum"><a name="Page_ii" id="Page_ii">[Pg ii]</a></span></p> + +<div class="caption2">ABSTRACT</div> + + +<p class="noidt">Mugaas, J. N., J. Seidensticker, and K. Mahlke-Johnson. Metabolic Adaptation to Climate and +Distribution of the Raccoon <i>Procyon lotor</i> and Other Procyonidae. <i>Smithsonian Contributions +to Zoology</i>, number 542, 34 pages, 8 figures, 12 tables, 1993.—Although the family +Procyonidae is largely a Neotropical group, the North American raccoon, <i>Procyon lotor</i>, is more +versatile in its use of climate, and it is found in nearly every habitat from Panama to 60°N in +Canada. We hypothesized that most contemporary procyonids have remained in tropic and +subtropic climates because they have retained the metabolic characteristics of their +warm-adapted ancestors, whereas <i>Procyon lotor</i> evolved a different set of adaptations that have +enabled it to generalize its use of habitats and climates. To test this hypothesis we compared +<i>Procyon lotor</i> with several other procyonids (<i>Bassariscus astutus</i>, <i>Nasua nasua</i>, <i>Nasua narica</i>, +<i>Procyon cancrivorus</i>, and <i>Potos flavus</i>) with respect to (1) basal metabolic rate (Ḣ<sub>b</sub>), (2) +minimum wet thermal conductance (C<sub>mw</sub>), (3) diversity of diet (D<sub>d</sub>), (4) intrinsic rate of natural +increase (r<sub>max</sub>), and, where possible, (5) capacity for evaporative cooling (E<sub>c</sub>). We measured +basal and thermoregulatory metabolism, evaporative water loss, and body temperature of both +sexes of <i>Procyon lotor</i> from north central Virginia, in summer and winter. Metabolic data for +other procyonids were from literature, as were dietary and reproductive data for all species.</p> + +<p>Procyon lotor differed from other procyonids in all five variables. (1) <i>Procyon lotor</i>'s mass +specific Ḣ<sub>b</sub> (0.46 mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>) was 1.45 to 1.86 times greater than values for other procyonids. +(2) Because of its annual molt, <i>Procyon lotor</i>'s C<sub>mw</sub> was about 49% higher in summer than +winter, 0.0256 and 0.0172 mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>·°C<sup>-1</sup>, respectively. The ratio of measured to predicted +C<sub>mw</sub> for <i>Procyon lotor</i> in winter (1.15) was similar to values calculated for <i>Potos flavus</i> (1.02) +and <i>Procyon cancrivorus</i> (1.25). Values for other procyonids were higher than this, but less than +the value for <i>Procyon lotor</i> (1.76) in summer. On a mass specific basis, <i>Bassariscus astutus</i> had +the lowest C<sub>mw</sub> with a ratio of 0.85. (3) <i>Procyon lotor</i> utilized three times as many food +categories as <i>Procyon cancrivorus</i>, <i>Nasua nasua</i>, and <i>Bassariscus astutus</i>; about two times as +many as <i>Nasua narica</i>; and nine times as many as <i>Potos flavus</i>. (4) Intrinsic rate of natural +increase correlated positively with Ḣ<sub>b</sub>. <i>Procyon lotor</i> had the highest r<sub>max</sub> (2.52 of expected) and +<i>Potos flavus</i> the lowest (0.48 of expected). The other procyonids examined also had low Ḣ<sub>b</sub>, but +their r<sub>max</sub>'s were higher than predicted (1.11-1.32 of expected). Early age of first female +reproduction, fairly large litter size, long life span, high-quality diet, and, in one case, female +social organization all compensated for low Ḣ<sub>b</sub> and elevated r<sub>max</sub>. (5) Although data on the +capacity for evaporative cooling were incomplete, this variable appeared to be best developed in +<i>Procyon lotor</i> and <i>Bassariscus astutus</i>, the two species that have been most successful at +including temperate climates in their distributions.</p> + +<p>These five variables are functionally interrelated, and have co-evolved in each species to form +a unique adaptive unit that regulates body temperature and energy balance throughout each +annual cycle. The first four variables were converted into normalized dimensionless numbers, +which were used to derive a composite score that represented each species' adaptive unit. +<i>Procyon lotor</i> had the highest composite score (1.47) and <i>Potos flavus</i> the lowest (0.39). Scores +for the other procyonids were intermediate to these extremes (0.64-0.79). There was a positive +correlation between the number of climates a species occupies and the magnitude of its +composite score. Linear regression of this relationship indicated that 89% of the variance in +climatic distribution was attributed to the composite scores. Differences in metabolic adaptation, +therefore, have played a role in delimiting climatic distribution of these species.</p> + +<p>It was clear that <i>Procyon lotor</i> differed from the other procyonids with respect to +thermoregulatory ability, diet, and reproductive potential. These differences have enabled it to +become a highly successful climate generalist, and its evolution of an Ḣ<sub>b</sub> that is higher than the +procyonid norm appears to be the cornerstone of its success.</p> +<br> + +<p class="noidt"> +<span class="smcap">Official publication date</span> is handstamped in a limited number of initial copies and is +recorded in the Institution's annual report, <i>Smithsonian Year</i>. <span class="smcap">Series cover design:</span> The coral +<i>Montastrea cavernosa</i> (Linnaeus).</p> + +<hr> +<p class="noidt"><small> +Library of Congress Cataloging-in-Publication Data<br> + +Mugaas, John N.<br> + +Metabolic adaptation to climate and distribution of the raccoon Procyon lotor and other Procyonidae / John N. Mugaas, +John Seidensticker, and Kathleen P. Mahlke-Johnson.<br> + +p. cm.—(Smithsonian contributions to zoology; no. 542)<br> + +Includes bibliographical references (p. )<br> + +1. Raccoons-Metabolism-Climatic factors. 2. Procyonidae-Metabolism-Climatic factors. 3. Raccoons-Geographical +distribution. 4. Procyonidae-Geographical distribution. I. Seidensticker, John. II. Mahlke-Johnson, +Kathleen. III. Title. IV. Series.<br> + +QL1.S54 no. 542 [QL737.C26] 591 s-dc20 [599.74´443´04542] 93-3119</small><br> +<br> + +<img src="images/perm_paper.png" width="22" height="21" title="permanent paper" alt="permanent paper"> The paper used in this publication meets the minimum requirements of the American +National Standard for Permanence of Paper for Printed Library Materials z39.48—1984.</p> + + +<br> +<br> +<p><span class="pagenum"><a name="Page_iii" id="Page_iii">[Pg iii]</a></span></p> +<a name="toc"></a> +<div class="caption2">Contents</div> + +<table width="100%" summary="ToC"> +<tr><td> </td><td class="text_rt"><i>Page</i></td></tr> +<tr><td><a href="#Introduction">Introduction</a></td><td class="text_rt">1</td></tr> +<tr><td> <a href="#Defining_the_Problem">Defining the Problem</a></td><td class="text_rt">1</td></tr> +<tr><td> <a href="#Procyonid_Origins">Procyonid Origins</a></td><td class="text_rt">1</td></tr> +<tr><td> <a href="#Typical_Procyonids">Typical Procyonids</a></td><td class="text_rt">2</td></tr> +<tr><td> <a href="#The_Atypical_Procyonid">The Atypical Procyonid</a></td><td class="text_rt">3</td></tr> +<tr><td> <a href="#The_Hypothesis">The Hypothesis</a></td><td class="text_rt">4</td></tr> +<tr><td> <a href="#Hypothesis_Testing">Hypothesis Testing</a></td><td class="text_rt">4</td></tr> +<tr><td> <a href="#Adaptive_Significance">Adaptive Significance of the Variables</a></td><td class="text_rt">4</td></tr> +<tr><td> <a href="#Basal_Metabolic_Rate_1">Basal Metabolic Rate and Intrinsic Rate of Natural Increase</a></td><td class="text_rt">4</td></tr> +<tr><td> <a href="#Minimum_Thermal_Conductance_1">Minimum Thermal Conductance</a></td><td class="text_rt">4</td></tr> +<tr><td> <a href="#Capacity_for_Evaporative_Cooling">Capacity for Evaporative Cooling</a></td><td class="text_rt">5</td></tr> +<tr><td> <a href="#Diet">Diet</a></td><td class="text_rt">5</td></tr> +<tr><td> <a href="#Experimental_Design_and_Summary">Experimental Design and Summary</a></td><td class="text_rt">5</td></tr> +<tr><td> <a href="#Acknowledgments">Acknowledgments</a></td><td class="text_rt">5</td></tr> +<tr><td><a href="#Materials_and_Methods">Materials and Methods</a></td><td class="text_rt">6</td></tr> +<tr><td> <a href="#Live-trapping">Live-trapping</a></td><td class="text_rt">6</td></tr> +<tr><td> <a href="#Metabolic_Studies">Metabolic Studies</a></td><td class="text_rt">6</td></tr> +<tr><td> <a href="#Basal_and_Thermoregulatory_Metabolism">Basal and Thermoregulatory Metabolism</a></td><td class="text_rt">6</td></tr> +<tr><td> <a href="#Evaporative_Water_Loss_1">Evaporative Water Loss</a></td><td class="text_rt">7</td></tr> +<tr><td> <a href="#Body_Temperature">Body Temperature</a></td><td class="text_rt">7</td></tr> +<tr><td> <a href="#Calibrations">Calibrations</a></td><td class="text_rt">7</td></tr> +<tr><td> <a href="#Calorimeter">Calorimeter</a></td><td class="text_rt">7</td></tr> +<tr><td> <a href="#Body_Temperature_Transmitters">Body Temperature Transmitters</a></td><td class="text_rt">8</td></tr> +<tr><td> <a href="#Statistical_Methods">Statistical Methods</a></td><td class="text_rt">8</td></tr> +<tr><td> <a href="#Estimating_Intrinsic_Rate">Estimating Intrinsic Rate of Natural Increase</a></td><td class="text_rt">8</td></tr> +<tr><td> <a href="#Comparison_of_Adaptive_Units">Comparison of Adaptive Units</a></td><td class="text_rt">8</td></tr> +<tr><td><a href="#Results">Results</a></td><td class="text_rt">8</td></tr> +<tr><td> <a href="#Body_Mass">Body Mass</a></td><td class="text_rt">8</td></tr> +<tr><td> <a href="#Basal_Metabolic_Rate_2">Basal Metabolic Rate</a></td><td class="text_rt">9</td></tr> +<tr><td> <a href="#Minimum_Thermal_Conductance_2">Minimum Thermal Conductance</a></td><td class="text_rt">9</td></tr> +<tr><td> <a href="#Evaporative_Water_Loss_2">Evaporative Water Loss</a></td><td class="text_rt">11</td></tr> +<tr><td> <a href="#Thermoregulation_at_Low_Temperatures">Thermoregulation at Low Temperatures</a></td><td class="text_rt">12</td></tr> +<tr><td> <a href="#Body_Temperature_1">Body Temperature</a></td><td class="text_rt">12</td></tr> +<tr><td> <a href="#Summer_1">Summer</a></td><td class="text_rt">14</td></tr> +<tr><td> <a href="#Winter_1">Winter</a></td><td class="text_rt">14</td></tr> +<tr><td> <a href="#Thermoregulation_at_High_Temperatures">Thermoregulation at High Temperatures</a></td><td class="text_rt">16</td></tr> +<tr><td> <a href="#Body_Temperature_2">Body Temperature</a></td><td class="text_rt">16</td></tr> +<tr><td> <a href="#Summer_2">Summer</a></td><td class="text_rt">16</td></tr> +<tr><td> <a href="#Winter_2">Winter</a></td><td class="text_rt">16</td></tr> +<tr><td> <a href="#Daily_Cycle_of_Body_Temperature">Daily Cycle of Body Temperature</a></td><td class="text_rt">16</td></tr> +<tr><td><a href="#Discussion">Discussion</a></td><td class="text_rt">16</td></tr> +<tr><td> <a href="#Basal_Metabolic_Rate_3">Basal Metabolic Rate</a></td><td class="text_rt">16</td></tr> +<tr><td> <a href="#Background_1">Background</a></td><td class="text_rt">16</td></tr> +<tr><td> <a href="#Captive_versus_Wild_Raccoons">Captive versus Wild Raccoons</a></td><td class="text_rt">17</td></tr> +<tr><td> <a href="#Seasonal_Metabolism_of_Raccoons">Seasonal Metabolism of Raccoons</a></td><td class="text_rt">17</td></tr> +<tr><td> <a href="#Comparison">Comparison of <i>Procyon lotor</i> with Other Procyonids</a></td><td class="text_rt">17</td></tr> +<tr><td> <a href="#Influence_of_Diet">Influence of Diet on Basal Metabolism</a><span class="pagenum"><a name="Page_iv" id="Page_iv">[Pg iv]</a></span></td><td class="text_rt">18</td></tr> +<tr><td> <a href="#Background_2">Background</a></td><td class="text_rt">18</td></tr> +<tr><td> <a href="#Food_Habits_of_Procyonids">Food Habits of Procyonids</a></td><td class="text_rt">18</td></tr> +<tr><td> <a href="#Food_Habits_and_Basal_Metabolism">Food Habits and Basal Metabolism</a></td><td class="text_rt">19</td></tr> +<tr><td> <a href="#Summary_1">Summary</a></td><td class="text_rt">19</td></tr> +<tr><td> <a href="#Basal_Metabolism_1">Basal Metabolism and Intrinsic Rate of Natural Increase</a></td><td class="text_rt">19</td></tr> +<tr><td> <a href="#Background_3">Background</a></td><td class="text_rt">19</td></tr> +<tr><td> <a href="#Procyon_lotor_1"><i>Procyon lotor</i></a></td><td class="text_rt">19</td></tr> +<tr><td> <a href="#Bassariscus_astutus_1"><i>Bassariscus astutus</i></a></td><td class="text_rt">19</td></tr> +<tr><td> <a href="#Nasua_narica_1"><i>Nasua narica</i></a></td><td class="text_rt">19</td></tr> +<tr><td> <a href="#Nasua_nasua_1"><i>Nasua nasua</i></a></td><td class="text_rt">20</td></tr> +<tr><td> <a href="#Procyon_cancrivorus_1"><i>Procyon cancrivorus</i></a></td><td class="text_rt">20</td></tr> +<tr><td> <a href="#Potos_flavus_1"><i>Potos flavus</i></a></td><td class="text_rt">20</td></tr> +<tr><td> <a href="#Summary_2">Summary</a></td><td class="text_rt">20</td></tr> +<tr><td> <a href="#Basal_Metabolism_2">Basal Metabolism and Climatic Distribution</a></td><td class="text_rt">21</td></tr> +<tr><td> <a href="#Procyon_lotor_2"><i>Procyon lotor</i></a></td><td class="text_rt">21</td></tr> +<tr><td> <a href="#Other_Procyonids">Other Procyonids</a></td><td class="text_rt">21</td></tr> +<tr><td> <a href="#Minimum_Thermal_Conductance_3">Minimum Thermal Conductance</a></td><td class="text_rt">21</td></tr> +<tr><td> <a href="#Background_4">Background</a></td><td class="text_rt">21</td></tr> +<tr><td> <a href="#Effect_of_Molt_on_Thermal_Conductance">Effect of Molt on Thermal Conductance</a></td><td class="text_rt">21</td></tr> +<tr><td> <a href="#Comparison_of_Thermal_Conductances">Comparison of Thermal Conductances</a></td><td class="text_rt">22</td></tr> +<tr><td> <a href="#Procyon_lotor_versus_Tropical_Procyonids"><i>Procyon lotor</i> versus Tropical Procyonids</a></td><td class="text_rt">22</td></tr> +<tr><td> <a href="#Bassariscus_astutus_2"><i>Bassariscus astutus</i></a></td><td class="text_rt">22</td></tr> +<tr><td> <a href="#Thermoregulation_1">Thermoregulation and Use of Stored Fat at Low Temperatures</a></td><td class="text_rt">22</td></tr> +<tr><td> <a href="#Background_5">Background</a></td><td class="text_rt">22</td></tr> +<tr><td> <a href="#Thermoregulation_2">Thermoregulation</a></td><td class="text_rt">22</td></tr> +<tr><td> <a href="#Stored_Fat">Stored Fat</a></td><td class="text_rt">23</td></tr> +<tr><td> <a href="#Thermal_Model">Thermal Model of the Raccoon and Its Den</a></td><td class="text_rt">23</td></tr> +<tr><td> <a href="#Metabolic_Advantage_of_the_Den">Metabolic Advantage of the Den</a></td><td class="text_rt">23</td></tr> +<tr><td> <a href="#Thermoregulation_3">Thermoregulation at High Temperatures</a></td><td class="text_rt">24</td></tr> +<tr><td> <a href="#Background_6">Background</a></td><td class="text_rt">24</td></tr> +<tr><td> <a href="#Comparison_of_Procyonid_Responses">Comparison of Procyonid Responses to Heat Stress</a></td><td class="text_rt">24</td></tr> +<tr><td> <a href="#Potos_flavus_2"><i>Potos flavus</i></a></td><td class="text_rt">24</td></tr> +<tr><td> <a href="#Nasua_nasua_2"><i>Nasua nasua and Nasua narica</i></a></td><td class="text_rt">24</td></tr> +<tr><td> <a href="#Bassariscus_astutus_3"><i>Bassariscus astutus</i></a></td><td class="text_rt">24</td></tr> +<tr><td> <a href="#Procyon_lotor_3"><i>Procyon lotor</i></a></td><td class="text_rt">24</td></tr> +<tr><td> <a href="#Procyon_cancrivorus_2"><i>Procyon cancrivorus</i></a></td><td class="text_rt">24</td></tr> +<tr><td> <a href="#Summary_3">Summary</a></td><td class="text_rt">24</td></tr> +<tr><td> <a href="#Composite_Scores">Composite Scores of Adaptive Units and Geographic Distribution</a></td><td class="text_rt">25</td></tr> +<tr><td> <a href="#Evolution_of_Metabolic_Adaptations">Evolution of Metabolic Adaptations</a></td><td class="text_rt">26</td></tr> +<tr><td> <a href="#Evolution_of_Low_Basal_Metabolic_Rate">Evolution of Low Basal Metabolic Rate</a></td><td class="text_rt">26</td></tr> +<tr><td> <a href="#Evolution_of_High_Basal_Metabolic_Rate">Evolution of High Basal Metabolic Rate</a></td><td class="text_rt">27</td></tr> +<tr><td> <a href="#Summary_4">Summary</a></td><td class="text_rt">28</td></tr> +<tr><td><a href="#Appendix_List_of_Symbols">Appendix: List of Symbols</a></td><td class="text_rt">29</td></tr> +<tr><td><a href="#Literature_Cited">Literature Cited</a></td><td class="text_rt">30</td></tr> +</table> + + +<br> +<br> +<p><span class="pagenum"><a name="Page_1" id="Page_1">[Pg 1]</a></span></p> + +<div class="caption2">Metabolic Adaptation to Climate<br> +and Distribution of the Raccoon<br> +<i>Procyon lotor</i> and Other Procyonidae</div> + +<div class="caption4">John N. Mugaas, John Seidensticker,<br> +and Kathleen P. Mahlke-Johnson</div> + +<div class="blockquot"> +<i>John N. Mugaas, Department of Physiology, Division of Functional +Biology, West Virginia School of Osteopathic Medicine, Lewisburg, +West Virginia 24901. John Seidensticker and Kathleen P. Mahlke-Johnson, +National Zoological Park, Smithsonian Institution, Washington, +D.C. 20008.</i> +</div> + + +<br> +<a name="Introduction"></a> +<a name="Defining_the_Problem"></a> +<a name="Procyonid_Origins"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption2">Introduction</div> +<div class="caption3"><span class="smcap">Defining the Problem</span></div> +<div class="caption4">Procyonid Origins</div> + +<p>The major carnivore radiations took place about 40 million +years before present (MYBP) in the late Eocene and early +Oligocene (Ewer, 1973:363; Wayne et al., 1989). Between 30 +and 40 MYBP, a progenitor split into the ursid and procyonid +lineages, which evolved into present-day bears, pandas, and +raccoons (Wayne et al., 1989). The taxonomic relatedness of +pandas to bears and raccoons has been tested extensively and a +number of authors have summarized current thinking on the +problem (Martin, 1989; Wayne et al., 1989; Wozencraft, +1989a, 1989b; Decker and Wozencraft, 1991). Davis +(1964:322-327) and others (Leone and Wiens, 1956; Todd and +Pressman, 1968; Sarich, 1976; O'Brien et al., 1985) place the +giant panda, <i>Ailuropoda melanoleuca</i>, with the ursids. The +taxonomic status of the red panda, <i>Ailurus fulgens</i>, appears to +be less certain. Some current investigations align the red panda +with bears (Segall, 1943; Todd and Pressman, 1968; Hunt, +1974; Ginsburg, 1982; Wozencraft, 1984:56-110; 1989a), +whereas others place them intermediate to procyonids and +bears (Wurster and Benirschke, 1968; Sarich, 1976; O'Brien et +al., 1985), or in close relationship to the giant panda (Tagle et +al., 1986).</p> + +<p>The procyonid radiation took place in North America and +produced forms that were mostly arboreal and omnivorous +(Eisenberg, 1981:122; Martin, 1989). The center of this +diversification occurred in Middle America (Baskin, 1982; +Webb, 1985b) during the Miocene (Darlington, 1963:367; +Webb, 1985b). Fossil procyonids from the late Miocene are +represented in Florida, California, Texas, Nebraska, Kansas, +and South Dakota (Baskin, 1982; Martin, 1989) and include +such genera as <i>Bassariscus</i>, <i>Arctonasua</i>, <i>Cyonasua</i>, <i>Paranasua</i>, +<i>Nasua</i>, and <i>Procyon</i> (Baskin, 1982; Webb, 1985b). +During the Miocene procyonids underwent a modest radiation +within tropical and subtropical climates of North America's +central and middle latitudes. <i>Cyonasua</i>, which has close +affinities to <i>Arctonasua</i> (Baskin, 1982), appears in tropical +South America in the late Miocene and immigrated there either +by rafting across the Bolivar Trough or by island-hopping +through the Antilles archipelagoes (Marshall et al., 1982; +Marshall, 1988). Thus, procyonids were found on both +continents prior to formation of the Panamanian land bridge +(Darlington, 1963:367, 395; Marshall et al., 1982; Marshall, +1988). Origins of <i>Bassaricyon</i> and <i>Potos</i> are obscure but +probably occurred in tropical rainforests of Middle America +(Baskin, 1982; Webb, 1985b). A subsequent Pleistocene +dispersal carried several modern genera (<a href="#Table_1">Table 1</a>) across the +Panamanian land bridge into South America (Webb, 1985b). +<i>Bassariscus</i> and <i>Bassaricyon</i> represent the most primitive +genera in Procyoninae and Potosinae subfamilies, respectively +(<a href="#Table_1">Table 1</a>; Wozencraft, 1989a; Decker and Wozencraft, 1991).</p> + +<p>In the early Tertiary, mid-latitudes of North America were +much warmer than they are now, but not fully tropical, and +temperate deciduous forests, associated with strongly seasonal +climates, occurred only in the far north (Barghoorn, 1953; +Colbert, 1953; Darlington, 1963:589, 590). Major climatic +deteriorations, with their attendant cooling of northern continents, +occurred during the Eo-Oligocene transition, in the +middle Miocene, at the end of the Miocene, and at about 3 +MYBP (late Pliocene). This last deterioration corresponds with +closure of the Panamanian isthmus (Berggren, 1982; Webb, +<span class="pagenum"><a name="Page_2" id="Page_2">[Pg 2]</a></span> +1985a). Climatic deterioration went on at an accelerating rate +during the late Tertiary, with glacial conditions developing at +the poles by the mid-Pliocene (Barghoorn, 1953). Therefore, +throughout the Tertiary, as continents cooled, northern climate +zones moved toward the tropics (Barghoorn, 1953; Colbert, +1953; Darlington, 1963:589, 590, 594, 595; Webb, 1985a).</p> + +<a name="Table_1"></a> +<div class="tab_cap"> +<span class="smcap">Table 1.</span>—Classification of recent Procyonidae after Wozencraft (1989a) and Decker and Wozencraft (1991). Information in parenthesis indicates general geographic distribution (modified from Kortlucke and Ramirez-Pulido (1982) and Poglayen-Neuwall (1975)): S.A. = South America; C.A. = Central America; M. = Mexico; U.S. = United States; C. = Canada. Lower case letters preceding geographic areas signify north (n), south (s), and west (w). +</div> + +<div class="blockquot"><p class="noidt"> +Order <span class="smcap">Carnivora</span> Bowdich, 1821<br> +<span style="margin-left: 1em;">Suborder <span class="smcap">Caniformia</span> Kretzoi, 1945</span><br> +<span style="margin-left: 2em;">Family <span class="smcap">Procyonidae</span> Gray, 1825</span><br> +<span style="margin-left: 3em;">Subfamily <span class="smcap">Potosinae</span> Trouessart, 1904</span><br> +<span style="margin-left: 4em;">Genus <i>Potos</i> E. Geoffroy and G. Cuvier, 1795</span><br> +<span class="m_left5"><i>P. flavus</i> (S.A., C.A., M.)</span><br> +<span style="margin-left: 4em;">Genus <i>Bassaricyon</i> Allen, 1876</span><br> +<span class="m_left5"><i>B. alleni</i><a name="FNanchor_A_2" id="FNanchor_A_2"></a><a href="#Footnote_A_2" class="fnanchor">[A]</a> (S.A.)</span><br> +<span class="m_left5"><i>B. beddardi</i><a href="#Footnote_A_2" class="fnanchor">[A]</a> (S.A.)</span><br> +<span class="m_left5"><i>B. gabbii</i><a href="#Footnote_A_2" class="fnanchor">[A]</a> (nS.A., C.A.)</span><br> +<span class="m_left5"><i>B. lasius</i><a href="#Footnote_A_2" class="fnanchor">[A]</a> (C.A.)</span><br> +<span class="m_left5"><i>B. pauli</i><a href="#Footnote_A_2" class="fnanchor">[A]</a> (C.A.)</span><br> +<span style="margin-left: 3em;">Subfamily <span class="smcap">Procyoninae</span> Gray, 1825</span><br> +<span style="margin-left: 4em;">Genus <i>Bassariscus</i> Coues, 1887</span><br> +<span class="m_left5"><i>B. astutus</i> (M., wU.S.)</span><br> +<span class="m_left5"><i>B. sumichrasti</i> (C.A., M.)</span><br> +<span style="margin-left: 4em;">Genus <i>Nasua</i> Storr, 1780</span><br> +<span class="m_left5"><i>N. narica</i><a name="FNanchor_B_3" id="FNanchor_B_3"></a><a href="#Footnote_B_3" class="fnanchor">[B]</a> (nS.A., C.A., M., swU.S.)</span><br> +<span class="m_left5"><i>N. nasua</i><a href="#Footnote_B_3" class="fnanchor">[B]</a> (S.A., sC.A.)</span><br> +<span style="margin-left: 4em;">Genus <i>Nasuella</i> Hollister, 1915</span><br> +<span class="m_left5"><i>N. olivacea</i> (S.A.)</span><br> +<span style="margin-left: 4em;">Genus <i>Procyon</i> Storr, 1780</span><br> +<span class="m_left5"><i>P. cancrivorus</i> (S.A., sC.A.)</span><br> +<span class="m_left5"><i>P. gloveralleni</i><a name="FNanchor_C_4" id="FNanchor_C_4"></a><a href="#Footnote_C_4" class="fnanchor">[C]</a> (Barbados)</span><br> +<span class="m_left5"><i>P. insularis</i><a href="#Footnote_C_4" class="fnanchor">[C]</a> (Maria Madre Is., Maria Magdalene Is.)</span><br> +<span class="m_left5"><i>P. lotor</i><a href="#Footnote_C_4" class="fnanchor">[C]</a> (C.A., M., U.S., sC.)</span><br> +<span class="m_left5"><i>P. maynardi</i><a href="#Footnote_C_4" class="fnanchor">[C]</a> (Bahamas, New Providence Is.)</span><br> +<span class="m_left5"><i>P. minor</i><a href="#Footnote_C_4" class="fnanchor">[C]</a> (Guadeloupe Is.)</span><br> +<span class="m_left5"><i>P. pygmaeus</i><a href="#Footnote_C_4" class="fnanchor">[C]</a> (M., Quintana Roo, Cozumel Is.)</span><br> +</p> +</div> + +<div class="footnote"> +<a name="Footnote_A_2" id="Footnote_A_2"></a><a href="#FNanchor_A_2"><span class="label">[A]</span></a> The several named forms of <i>Bassaricyon</i> are a single species, <i>Bassaricyon gabbii</i> (Wozencraft, 1989a).<br> +<br> +<a name="Footnote_B_3" id="Footnote_B_3"></a><a href="#FNanchor_B_3"><span class="label">[B]</span></a> These are considered conspecific in some current taxonomies (Kortlucke and Ramirez-Pulido, 1982); however, the scheme followed here maintains them as separate species (Decker, 1991).<br> +<br> +<a name="Footnote_C_4" id="Footnote_C_4"></a><a href="#FNanchor_C_4"><span class="label">[C]</span></a> Several named forms of <i>Procyon</i> are a single species, <i>Procyon lotor</i> (Wozencraft, 1989a).<br> +<br> +</div> + + +<p>During the late Miocene, late Pliocene, and Pleistocene, the +Bering land bridge between North America and Asia formed +periodically, offering an avenue for dispersal between northern +continents (Darlington, 1963:366; Webb, 1985a). However, by +the late Tertiary, northern continents had cooled to the extent +that climate, with its attendant sharply defined vegetative +zones, became the major factor limiting dispersal by this route +(Darlington, 1963:366; Webb, 1985a). Those Holarctic mammals +that did cross the Bering land bridge in the late Tertiary +were "cold-adapted" species associated with relatively cool, +but not alpine, climates (Darlington, 1963:366; Ewer, +1973:369). Among carnivores this included some canids, +ursids, mustelids, and felids (Darlington, 1963:393-395, 397; +Webb, 1985a). Procyonids, however, did not cross the Bering +land bridge into Asia, and Ewer (1973:369) ascribes this to +their being an "essentially tropical group." Miocene radiation +of procyonids occurred at a time when two of the four major +climatic deteriorations (middle and late Miocene) were taking +place (Webb, 1985a, 1985b). These deteriorations had the +effect of cooling the middle latitudes to the extent that +temperate forest forms began to appear in mid-latitude floras, +along with a rapid influx of herbaceous plants (Barghoorn, +1953). The procyonid radiation did not penetrate beyond these +climatically changing middle latitudes, which implies that +these animals were "warm-adapted," and were, therefore, +physiologically excluded from reaching the Bering land bridge. +Today, three of the six genera and over half of the 18 species +that comprise Procyonidae (<a href="#Table_1">Table 1</a>; Wozencraft, 1989b) +remain confined to tropical regions of North and South +America (Hall and Kelson, 1959:878-897; Poglayen-Neuwall, +1975; Kortlucke and Ramirez-Pulido, 1982; Nowak and +Paradiso, 1983:977-985).</p> + + + +<a name="Typical_Procyonids"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Typical Procyonids</div> + +<p>McNab (1988a) contends that basal metabolism is a highly +plastic character in evolution, and he has amply shown that +ecologically uniform species are more apt to share common +metabolic rates than taxonomically allied species from drastically +different environments (McNab, 1984a, 1986a, 1986b, +1988a). Procyonids represent a taxonomically allied group that +shared a common ecological situation for millions of years; +consequently, members of this family might be expected to +show some uniformity in their Ḣ<sub>b</sub>. Basal and thermoregulatory +metabolism of several procyonids have been measured: +kinkajou, <i>Potos flavus</i> (Müller and Kulzer, 1977; McNab, +1978a; Müller and Rost, 1983), coatis, <i>Nasua nasua</i> (Chevillard-Hugot +et al., 1980; Mugaas et al., in prep.), and <i>Nasua +narica</i> (Scholander et al., 1950c; Mugaas et al., in prep.), +ringtail, <i>Bassariscus astutus</i> (Chevalier, 1985), and crab-eating +raccoon, <i>Procyon cancrivorus</i> (Scholander et al., 1950c). In +general, these species have Ḣ<sub>b</sub>'s that are 40%-80% of the +values predicted for them by the Kleiber (1961:206) equation. +Lower than predicted Ḣ<sub>b</sub> is viewed as an energy-saving +adaptation for procyonids living in relatively stable tropical +climates (Müller and Kulzer, 1977; Chevillard-Hugot et al., +1980; Müller and Rost, 1983). This implies that lower than +predicted Ḣ<sub>b</sub> is a general procyonid condition and that it +represents a characteristic that evolved in response to the +family's long association with tropical and subtropical forest +environments.<span class="pagenum"><a name="Page_3" id="Page_3">[Pg 3]</a></span></p> + + +<a name="The_Atypical_Procyonid"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">The Atypical Procyonid</div> + +<p>Although most procyonids are found in only tropical to +subtropical climates, the North American raccoon, <i>Procyon +lotor</i>, (<a href="#Fig_1">Figure 1</a>) has a much broader distribution that extends +from tropical Panama (8°N) to southern Canada. In Alberta, +Canada, its range reaches the edge of the Hudsonian Life Zone +at 60°N (for distribution maps see Hall and Kelson, 1959:878-897, +and Poglayen-Neuwall, 1975). Range extensions and an +increase in numbers have been noted in Canada and in parts of +the United States since the 19th century (Lotze and Anderson, +1979; Kaufmann, 1982; Nowak and Paradiso, 1983:977-985). +Thus, <i>Procyon lotor</i> is more complex ecologically than other +procyonids, particularly when one takes into account its highly +generalized food habits (Hamilton, 1936; Stuewer, 1943; +Stains, 1956:39-51; Greenwood, 1981) and the wide range of +habitat types (forest, prairie, desert, mountain, coastal marsh, +freshwater marsh) and climates (tropical to north temperate) in +which it is successful (Whitney and Underwood, 1952:1; Hall +and Kelson, 1959:885; Lotze and Anderson, 1979; Kaufmann, +1982). On this basis it is clear that <i>Procyon lotor</i> has deviated +from the typical procyonid portrait and has become the +consummate generalist of the Procyonidae.</p> + +<a name="Fig_1"></a> +<div class="center"> + <img src="images/fig_1.png" width="459" height="593" title="North American raccoon" alt="North American raccoon"><br><br> + <div class="center"><b><span class="smcap">Figure 1.</span>—North American raccoon, <i>Procyon lotor</i>.</b></div> +</div> + + +<a name="The_Hypothesis"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">The Hypothesis</div> + +<p><span class="pagenum"><a name="Page_4" id="Page_4">[Pg 4]</a></span>Our +general hypothesis was that whereas most contemporary +procyonids have retained the metabolic characteristics of their +warm-adapted ancestors, <i>Procyon lotor</i> possesses a different +set of adaptations, which either evolved as characteristics +unique to this species or were acquired from its ancestral stock. +In either case, its unique adaptations have given <i>Procyon lotor</i> +the physiological flexibility to generalize its use of habitats and +climates and expand its geographic distribution to a much +greater extent than other procyonids.</p> + +<a name="Hypothesis_Testing"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Hypothesis Testing</div> + +<p>We tested our hypothesis by comparing <i>Procyon lotor</i> with +several other procyonids (<i>Bassariscus astutus</i>, <i>Nasua nasua</i>, +<i>Nasua narica</i>, <i>Procyon cancrivorus</i>, and <i>Potos flavus</i>) on the +basis of their (1) basal metabolic rate (Ḣ<sub>b</sub>), (2) minimum wet +thermal conductance (C<sub>mw</sub>), (3) diversity of diet (D<sub>d</sub>), (4) +intrinsic rate of natural increase (r<sub>max</sub>), and, when data were +available, (5) capacity for evaporative cooling (E<sub>c</sub>). In a genetic +sense each one of these variables is a complex adaptive +characteristic, expression of which is determined by the +interaction of several genes (Prosser, 1986:110-165). Experience +has shown that a given species will express each one of +these variables in a specific manner that is relevant to its mass, +physiology, behavior, and environmental circumstance. Thus, +different expressions of these variables may represent specific +climatic adaptations (Prosser, 1986:16) that have been selected-for +by evolutionary process. Because these variables are +interrelated with respect to regulation of body temperature and +energy balance, they have co-evolved in each species to form +an adaptive unit. For each species, measured and calculated +values for the first four variables were converted into +dimensionless numbers and used to derive a composite score +that represented its adaptive unit. Climatic distributions of +these species were then compared relative to their composite +scores.</p> + +<a name="Adaptive_Significance"></a> +<a name="Basal_Metabolic_Rate_1"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Adaptive Significance of the Variables</div> +<div class="caption4">Basal Metabolic Rate and Intrinsic Rate of Natural Increase</div> + +<p>Basal metabolic rate represents the minimum energy +required by an animal to maintain basic homeostasis (Lusk, +1917:141; Kleiber, 1932, 1961:251; Benedict, 1938; Brody, +1945:59; Robbins, 1983:105-111). For mammals, Ḣ<sub>b</sub> appears +to be determined by complex interactions between their body +size (Kleiber, 1932, 1961:206; Benedict, 1938; Brody, +1945:368-374; Hemmingsen, 1960:15-36; McNab, 1983b; +Calder, 1987), the climate in which they live (Scholander et al., +1950c; McNab and Morrison, 1963; Hulbert and Dawson, +1974; Shkolnik and Schmidt-Nielsen, 1976; McNab, 1979a; +Vogel, 1980), their food habits (McNab, 1978a, 1978b, 1980a, +1983a, 1984a, 1986a, 1986b, 1988a, 1989), and their circadian +period (Aschoff and Pohl, 1970; Prothero, 1984). Some species +have higher mass-specific Ḣ<sub>b</sub> than others, and this variation +appears to be tied to ecological circumstances rather than +taxonomic affinities (McNab, 1988a, 1989). Basal metabolic +rate is important ecologically because it serves as a measure of +a species' minimum "obligatory" energy requirement, and +under many circumstances, it represents the largest energy +demand associated with a daily energy budget (King, 1974:38-55; +McNab, 1980a; Mugaas and King, 1981:37-40). Recently +it also has been implicated as a permissive factor with respect +to r<sub>max</sub> of mammals (Hennemann, 1983; Lillegraven et al., +1987; Nicoll and Thompson, 1987; Thompson, 1987) via its +direct effect on their rates of development and fecundity +(McNab, 1980a, 1983a, 1986b; Hennemann, 1983; Schmitz +and Lavigne, 1984; Glazier, 1985a, 1985b). The implication of +this latter point is that those species with higher Ḣ<sub>b</sub>'s also have +faster rates of development and greater fecundity and hence +enjoy the competitive advantage of a higher r<sub>max</sub>. Basal +metabolism is, therefore, "a highly plastic character in the +course of evolution" (McNab, 1988a:25) that has a profound +influence on each species' life history.</p> + +<a name="Minimum_Thermal_Conductance_1"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Minimum Thermal Conductance</div> + +<p>Whole-body resistance to passive heat transfer is equal to +tissue resistance plus coat resistance. Within limits, these +resistances can be altered; tissue resistance can be varied by +changes in blood flow, whereas coat resistance can be changed +by piloerection, molt, and behavior. When whole-body +resistance is maximized (maximum tissue and coat resistances), +passive heat transfer is minimized. The inverse of resistance is +conductance; therefore, maximum whole-body resistance is the +inverse of minimum thermal conductance (C<sub>m</sub>). Minimum +thermal conductance is readily derived from metabolic chamber +data, and it is commonly used to describe an animal's +capacity to minimize passive heat transfer. Minimum thermal +conductance interacts with Ḣ<sub>b</sub> and body mass to set the +maximum temperature differential a mammal can maintain +without increasing its basal level of heat production. The low +temperature in this differential is the lower critical temperature +(T<sub>lc</sub>).</p> + +<p>Mass-specific C<sub>m</sub> for mammals is negatively correlated with +body mass (McNab and Morrison, 1963; Herreid and Kessel, +1967; McNab, 1970, 1979b; Bradley and Deavers, 1980; +Aschoff, 1981), and for any given mass its magnitude is 52% +higher during the active, rather than the inactive, phase of the +daily cycle (Aschoff, 1981). However, some mammals have +C<sub>m</sub>'s that are higher or lower than would be predicted for them +on the basis of body mass and circadian phase. Seasonal +<span class="pagenum"><a name="Page_5" id="Page_5">[Pg 5]</a></span> +variation in C<sub>m</sub> (higher values during summer than winter) has +been reported for many northern mammals that experience +large annual variations in air temperature (Scholander et al., +1950a; Irving et al., 1955; Hart, 1956, 1957; Irving, 1972:165). +Some tropical mammals with very thin fur coats, and others +with nearly hairless bodies, have high C<sub>m</sub>'s (McNab, 1984a), as +do burrowing mammals (McNab, 1966, 1979b, 1984a) and the +kit fox, <i>Vulpes macrotis</i> (Golightly and Ohmart, 1983). Some +small mammals with low basal metabolic rates tend to have +lower than predicted C<sub>m</sub>'s: small marsupials (McNab, 1978a), +heteromyid rodents (McNab, 1979a), several ant eaters +(McNab, 1984a), the arctic hare, <i>Lepus arcticus</i> (Wang et al., +1973), the ringtail, <i>Bassariscus astutus</i> (Chevalier, 1985), and +the fennec, <i>Fennecus zerda</i> (Noll-Banholzer, 1979). Thus, in +spite of its mass dependence, C<sub>m</sub> also has been modified during +the course of evolution by selective factors in the environment +and by the animal's own metabolic characteristics.</p> + +<a name="Capacity_for_Evaporative_Cooling"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Capacity for Evaporative Cooling</div> + +<p>Latent heat loss occurs as a result of evaporation from the +respiratory tract and through the skin, and except under +conditions of heat stress, it "is a liability in thermal and osmotic +homeostasis" (Calder and King, 1974:302). E<sub>c</sub>, defined as the +ratio of evaporative heat lost to metabolic heat produced, can be +used to quantify thermoregulatory effectiveness of evaporative +cooling and to make comparisons of heat tolerance between +species. Thermoregulatory effectiveness of latent heat loss is +not just a function of the rate of evaporative water loss but also +of the rate of metabolic heat production (Lasiewski and +Seymour, 1972). For example, a low metabolic rate minimizes +endogenous heat load and thus conserves water, whereas the +opposite is true of high metabolic rates (Lasiewski and +Seymour, 1972). Some mammals that live in arid regions have +evolved low metabolic rates and thus capitalize on this +relationship to reduce their thermoregulatory water requirement +(McNab and Morrison, 1963; McNab, 1966; MacMillen +and Lee, 1970; Noll-Banholzer, 1979). What is evident, +therefore, is that an animal's capacity for increasing latent heat +loss must evolve together with its Ḣ<sub>b</sub> and C<sub>m</sub> in response to +specific environmental demands.</p> + +<a name="Diet"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Diet</div> + +<p>McNab (1986a, 1988a, 1989) demonstrated that, for mammals, +departures of Ḣ<sub>b</sub> from the Kleiber (1961:206) "norm" are +highly correlated with diet and independent of phylogenetic +relationships. McNab's analysis indicates that for mammals +that feed on invertebrates, those species with body mass less +than 100 g have Ḣ<sub>b</sub>'s that are equal to or greater than values +predicted by the Kleiber equation, whereas those with body +mass greater than 100 g have metabolic rates that are lower than +predicted. Grazers, vertebrate eaters, nut eaters, and terrestrial +frugivores also have Ḣ<sub>b</sub>'s that are equal to or greater than +predicted, whereas insectivorous bats, arboreal folivores, +arboreal frugivores, and terrestrial folivores all have rates that +are lower than predicted. McNab (1986a) found animals with +mixed diets harder to categorize, but in general he predicted +that their Ḣ<sub>b</sub>'s would be related to (1) a food item that is +constantly available throughout the year, (2) a food item that is +most available during the worst conditions of the year, or (3) a +mix of foods available during the worst time of the year. +Although these correlations do not establish cause and effect +between food habits and Ḣ<sub>b</sub>, McNab's analysis does make it +clear that the relationship between these variables has very real +consequences for an animal's physiology, ecology, and +evolution.</p> + +<a name="Experimental_Design_and_Summary"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Experimental Design and Summary</div> + +<p>In this investigation we measured basal and thermoregulatory +metabolism, evaporative water loss, and body temperature +of raccoons from north central Virginia. Measurements were +conducted on both sexes in summer and winter to determine +how season and sex influenced these variables. We then +compared the data for this widely distributed generalist with +data from literature for its ecologically more restricted +relatives. Dietary data for all species were taken from literature, +as were reproductive data for calculation of r<sub>max</sub>.</p> + +<p>Our analysis demonstrated clear differences between <i>Procyon +lotor</i> and other procyonids with respect to Ḣ<sub>b</sub>, C<sub>mw</sub>, D<sub>d</sub>, +and r<sub>max</sub>. The composite score calculated from these variables +for <i>Procyon lotor</i> was much higher than those derived for other +species, and there was a positive correlation between the +number of climates a species occupies and the magnitude of its +composite score. Data on evaporative water loss, although not +complete for all species, suggested that tropical and subtropical +procyonids have less capacity for evaporative cooling than +<i>Procyon lotor</i> or <i>Bassariscus astutus</i>. It was clear, therefore, +that with respect to its thermal physiology, <i>Procyon lotor</i> +differed markedly from other procyonids, and we contend that +these differences have allowed this species to become a highly +successful climate generalist and to expand its distribution into +many different habitats and climates. Our analysis also +suggested that the cornerstone of <i>Procyon lotor</i>'s success as a +climate generalist is its Ḣ<sub>b</sub>, which is higher than the procyonid +norm.</p> + +<a name="Acknowledgments"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Acknowledgments</div> + +<p>The authors would like to thank John Eisenberg and Devra +Kleiman for their support and encouragement throughout the +study. This investigation was supported by research grants +from the West Virginia School of Osteopathic Medicine +(WVSOM), and Friends of the National Zoo (FONZ). Logistic +support was provided by the National Zoological Park's +Conservation and Research Center (CRC), and the departments +of Mammalogy and Zoological Research. Our ability to +<span class="pagenum"><a name="Page_6" id="Page_6">[Pg 6]</a></span> +conduct physiological research at CRC was made possible by +the thoughtful support and encouragement provided by Chris +Wemmer. His excellent staff at CRC, especially Jack Williams, +Junior Allison, and Red McDaniel, were very helpful in +providing hospitality and logistical support to the senior author +and his family during their various visits to the Center. The +assistance of several people at the National Zoo also is +gratefully acknowledged: Mitch Bush and Lyndsay Phillips not +only provided veterinary support throughout the investigation, +but also performed surgical procedures required to implant +temperature-sensitive radio transmitters in several raccoons; +Olav Oftedal made his laboratory available to us at various +times and loaned us equipment to use at CRC; Miles Roberts +and his staff provided care for our captive raccoons in the +Department of Zoological Research during various parts of the +investigation. Greg Sanders and Ken Halama, supported by +FONZ assistantships, cared for our captive raccoons at CRC, +provided assistance in the laboratory whenever needed, and +were an invaluable source of aid. Their friendship and help is +gratefully acknowledged. Ellen Broudy and Andy Meyer, +supported by WVSOM and a student work study grant, +respectively, provided assistance in the laboratory. David +Brown, John Eisenberg, Mary Etta Hight, Brian McNab, Steve +Thompson, and W. Chris Wozencraft critically reviewed +various phases of the manuscript and provided many helpful +suggestions. We deeply appreciate the work of Jean B. +McConville, whose beneficial editorial suggestions helped us +improve several early versions of the manuscript. We also +gratefully acknowledge Diane M. Tyler, our editor at the +Smithsonian Institution Press, whose expertise helped us mold +the manuscript into its final form. Jill Mellon and Sriyanie +Miththalapa, supported by FONZ traineeships, assisted in +measuring the daily cycle of body temperature in raccoons. The +Virginia Commission of Game and Inland Fisheries gave us +permission to use wild-caught raccoons in this project.</p> + + + +<br> +<a name="Materials_and_Methods"></a> +<a name="Live-trapping"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption2">Materials and Methods</div> +<div class="caption3">Live-trapping</div> + +<p>Raccoons were caught from May 1980 through December +1984 on a trapping grid of 30 to 35 stations (one or two "live +traps" per station) that covered about one-third of the National +Zoological Park's Conservation and Research Center (CRC) +near Front Royal, Virginia (Seidensticker et al., 1988; Hallett et +al., 1991). Animals were trapped during 10 consecutive days +each month, and in this five-year interval 407 raccoons were +captured and marked with tattoos and ear tags. All captured +animals were individualized with respect to age, reproductive +status, physical condition, parasite load, and mass and body +dimensions. These data characterized the structure and dynamics +of the raccoon population at CRC and provided information +on the annual cycle of fattening for raccoons in north central +Virginia.</p> + +<p>Animals used for metabolic measurements were captured at +CRC about 1.5 km south of the trapping grid and thus were +genetically representative of the area. Six males were captured +and measured during the summer of 1983. These animals were +kept isolated for a week before being measured and were +released later that summer at the site of their capture. The other +seven animals used in our study were from the collection of the +National Zoological Park and all of them had their origins at CRC.</p> + +<a name="Metabolic_Studies"></a> +<a name="Basal_and_Thermoregulatory_Metabolism"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Metabolic Studies</div> +<div class="caption4">Basal and Thermoregulatory Metabolism</div> + +<p>Metabolic measurements, conducted at CRC, were carried +out on eight males during July and August 1983, on four +females and three males from November 1983 through March +1984, and on four females during June and July 1984.</p> + +<p>Raccoons were housed throughout the study such that they +were constantly exposed to a natural cycle of temperature and +photoperiod. Weather records for the Front Royal area indicate +that average temperatures are around -0.5°C in January and +23.3°C in July (Crockett, 1972). Light:dark (L:D) periods for +the latitude of CRC (48°55'N; United States Department of the +Interior Geological Survey, 1972), calculated from duration of +daylight tables (List, 1971:506-512), were 14.9:9.1 and +9.4:14.6 hours L:D for summer and winter solstices, +respectively, and 12.2:11.8 hours L:D for vernal and autumnal +equinoxes.</p> + +<p>Our animals were fed a measured amount of food daily, and +they usually ate most of what was provided. Occasionally these +animals would eat very little or none of their ration, and on +some days they would eat all that was given to them. We fed +them either feline diet (ground horse meat) or canned mackerel +(Star-kist<span class="sup2">®</span><a name="FNanchor_A_5" id="FNanchor_A_5"></a><a href="#Footnote_A_5" class="fnanchor">[1]</a>) along with high-protein dog chow (Purina<span class="sup2">®</span>). +When available, fresh fruit also was added to their diet. Water +was always provided ad libitum.</p> + +<div class="footnote"> +<a name="Footnote_A_5" id="Footnote_A_5"></a><a href="#FNanchor_A_5"><span class="label">[1]</span></a> <i>The use of product brand names in this publication is not intended as an endorsement of the products by the Smithsonian Institution.</i> +</div> + +<p>Measurements were conducted during the raccoons' daily +inactive period (sunrise to sunset) in both summer and winter. +Oxygen consumption was measured in a flow-through metabolism +chamber at 5°C intervals from -10°C to 35°C. Animals +were held at each temperature until the lowest rate of oxygen +consumption had been obtained and maintained for at least 15 +minutes. During each determination, oxygen consumption was +monitored for 30 minutes to one hour beyond a suspected +minimum value to see if an even lower reading could be +obtained. Raccoons attained minimum levels of oxygen +consumption more quickly at warm (>10°C) than at cold +<span class="pagenum"><a name="Page_7" id="Page_7">[Pg 7]</a></span> +temperatures. Depending on the temperature, therefore, each +measurement took from two to five hours to complete. On days +when two measurements could be completed, the second trial +was always at a temperature 10°C warmer than the first.</p> + +<p>The metabolism chamber was constructed from galvanized +sheet metal (77.5 × 45.5 × 51.0 cm = 180 liters) and was painted +black inside. Within the chamber, the animal was held in a cage +(71 × 39 × 33 cm) constructed from turkey wire that also was +painted black. This cage prevented the raccoons from coming +into contact with the walls of the chamber, yet it was large +enough to allow them to stand and freely move about. The +bottom of the cage was 11 cm above the chamber floor, which +was covered to a depth of one cm with mineral oil to trap urine +and feces.</p> + +<p>During measurements, the metabolism chamber was placed +in a controlled-temperature cabinet (modified Montgomery +Ward model 8969 freezer). Air temperature (T<sub>a</sub>) in the +metabolism chamber was regulated with a Yellow Springs +Instrument model 74 temperature controller. T<sub>a</sub> was controlled +to ± 1.0°C at temperatures below freezing, and to ± 0.5°C at +temperatures above freezing. The chamber air and wall +temperatures were recorded continuously (Linseis model +LS-64 recorder) during each experiment, and, except during +temperature changes, they were always within 0.5°C of each +other.</p> + +<p>Columns of Drierite<span class="sup2">®</span> and Ascarite<span class="sup2">®</span> removed water vapor +and carbon dioxide, respectively, from air entering and leaving +the chamber. Dry carbon-dioxide-free room air was pumped +into the chamber (Gilman model 13152 pressure/vacuum +pump) at a rate of 3.0 L/min (Gilmont model K3203-20 flow +meter). Downstream from the chemical absorbents, an aliquot +(0.1 L/min) of dry carbon-dioxide-free air was drawn off the +chamber exhaust line and analyzed for oxygen content +(Applied Electrochemistry model S-3A oxygen analyzer, +model 22M analysis cell, and model R-1 flow control). All gas +values were corrected to standard temperature and pressure for +dry gas. Oxygen consumption was calculated from the +difference in oxygen content between inlet and outlet air using +Eq. 8 of Depocas and Hart (1957).</p> + +<p>Each raccoon was fasted for at least 12 hours before oxygen +consumption measurements began. At the start and end of each +metabolic trial the animal was weighed to the nearest 10 g +(Doctors Infant Scale, Detecto Scales, Inc., Brooklyn, N.Y., +U.S.A.). The body mass used in calculating minimum oxygen +consumption and evaporative water loss was estimated from +timed extrapolations of the difference between starting and +ending weights, and the time at which these variables were +measured.</p> + + +<a name="Evaporative_Water_Loss_1"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Evaporative Water Loss</div> + +<p>During metabolic measurements at temperatures above +freezing, evaporative water loss was determined gravimetrically. +Upstream from the chemical columns, an aliquot of air +(0.1 L/min) was drawn off the exhaust line and diverted for a +timed interval through a series of preweighed (0.1 mg) <img src="images/u_tube.png" width="14" height="14" border="0" alt="U-tube" title="U-tube">-tubes +containing Drierite<span class="sup2">®</span>. The aliquot then passed through a second +series of <img src="images/u_tube.png" width="14" height="14" border="0" alt="U-tube" title="U-tube">-tubes containing Ascarite<span class="sup2">®</span> before entering the +oxygen analysis system. Evaporative water loss was calculated +using <a href="#Eq_1">Eq. 1</a></p> + +<a name="Eq_1"></a> +<table width="100%" summary="Eq. 1"> +<tr><td class="center">Ė = (m<sub>w</sub>·<span class="dot">.</span><span class="V">V</span><sub>e</sub>)/(<span class="dot">.</span><span class="V">V</span><sub>a</sub>·t·m)</td><td class="text_rt">Eq. 1</td></tr> +</table> + +<p class="noidt"> +where Ė is evaporative water loss (mg·g<sup>-1</sup>·h<sup>-1</sup>), m<sub>w</sub> is mass of +water collected (mg), <span class="dot">.</span><span class="V">V</span><sub>e</sub> is rate of air flow into the chamber (3.0 +L/min), <span class="dot">.</span><span class="V">V</span><sub>a</sub> is the rate of air flow through the <img src="images/u_tube.png" width="14" height="14" border="0" alt="U-tube" title="U-tube">-tubes (0.1 L/min), +t is length of the timed interval (h), and m is the estimated mass +of the raccoon at the time of sampling (g).</p> + +<a name="Body_Temperature"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Body Temperature</div> + +<p>Veterinarians at the National Zoological Park surgically +implanted calibrated temperature-sensitive radio transmitters +(Telonics, Inc., Mesa, AZ, U.S.A.) into abdominal cavities of +two female and two male raccoons. Transmitter pulse periods +were monitored with a digital processor (Telonics TDP-2) +coupled to a receiver (Telonics TR-2-164/166). During some +metabolic measurements, body temperatures of these animals +were recorded to the nearest 0.1°C at 30-minute intervals. The +daily cycle of body temperature of these raccoons also was +measured once a month.</p> + +<a name="Calibrations"></a> +<a name="Calorimeter"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Calibrations</div> +<div class="caption4">Calorimeter</div> + +<p>At the conclusion of these experiments, the accuracy of our +calorimetry apparatus was tested by burning an ethanol lamp in +the metabolism chamber. During these tests a CO<sub>2</sub> analyzer was +incorporated into the system (Beckman, LB-2). Results +demonstrated that we measured 84% of the oxygen consumed +by the lamp as well as 84% of the water and CO<sub>2</sub> it produced; +standard deviation = ± 2.6, ± 5.0, and ± 3.6, respectively (n = +27). Average respiratory quotient (RQ) calculated from these +data was O.657 ± 0.008 (n = 27), which is 99.5% of that +predicted (0.66). McNab (1988b) reports that the accuracy of +open-flow indirect calorimetry systems, such as ours, depends +on the rate of air flow through the animal chamber. If flow rates +are too low, there is inadequate mixing of air within the +chamber, and the rate of oxygen consumption, as calculated +from the difference in oxygen content of air flowing into and +out of the chamber (Depocas and Hart, 1957), is underestimated. +At some critical rate of air flow, which is unique to each +combination of chamber and animal, this situation changes +such that measured rates of oxygen consumption become +independent of any further increase in flow rate (McNab, +1988b). In recent tests of our system, where we burned the +ethanol lamp at a variety of chamber flow rates, the efficiency +<span class="pagenum"><a name="Page_8" id="Page_8">[Pg 8]</a></span> +of measurement increased linearly as flow rate increased, and +the critical rate of air flow was about 6.7 L/min. This appeared +to explain why a flow rate of 3.0 L/min underestimated oxygen +consumption of the ethanol lamp.</p> + +<p>Our earlier tests of the efficiency of our system indicated that +although we underestimated actual oxygen consumption of the +ethanol lamp, we did so with a fair degree of precision; +probably because flow rates were closely controlled. During +our metabolic measurements, chamber flow rates also were +closely controlled at 3.0 L/min, and we believe, therefore, that +these measurements also were carried out with a high degree of +precision. Consequently, all measured values of oxygen +consumption and water production were considered to be 84% +of their actual value and were adjusted to 100% before being +included in this report.</p> + +<a name="Body_Temperature_Transmitters"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Body Temperature Transmitters</div> + +<p>The calibration of all temperature-sensitive radio transmitters +drifted over time. Transmitters were calibrated before they +were surgically implanted and again after they were removed +from the animals. Although the drift of each transmitter was +unique, it was also linear (S. Tomkiewicz, Telonics, Inc., pers. +com.). All body temperature measurements were corrected +from timed extrapolations of the difference between starting +and ending calibrations.</p> + +<a name="Statistical_Methods"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Statistical Methods</div> + +<p>Values of oxygen consumption, evaporative water loss, and +body temperature were plotted as a function of chamber air +temperature. Linear regressions of oxygen consumption at +temperatures below the thermoneutral zone (T<sub>n</sub>), and evaporative +water loss at temperatures above freezing, were determined +with the SAS (1982) GLM procedure. Lower critical temperature +(T<sub>lc</sub>) was determined graphically from intersection of the +line representing Ḣ<sub>b</sub> and the regression line representing +oxygen consumption below T<sub>n</sub>. Slopes and intercepts of +regression lines, as well as other mean values, were compared +with <i>t</i>-tests (Statistical Analysis System, 1982; Ott, 1984:138-175). +Unless indicated otherwise, data are expressed as mean +± standard deviation (s.d.).</p> + +<a name="Estimating_Intrinsic_Rate"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Estimating Intrinsic Rate of Natural Increase</div> + +<p>We employed the method first described by Cole (1954) to +calculate r<sub>max</sub>:</p> + +<a name="Eq_2"></a> +<table width="100%" summary="Eq. 2"> +<tr><td class="center">1 = e<sup>-r<sub>max</sub></sup> + b·e<sup>-r<sub>max</sub>(a)</sup> - b·e<sup>-r<sub>max</sub>(n+1)</sup></td><td class="text_rt">Eq. 2</td></tr> +</table> + +<p class="noidt">where a is potential age of females first producing young, b is +potential annual birth rate of female young, and n is potential +age of females producing their final young. After life-history +data were substituted into <a href="#Eq_2">Eq. 2</a>, r<sub>max</sub> was determined by trial +and error substitution (Hennemann, 1983).</p> + +<p>Because r<sub>max</sub> represents the genetically fixed, physiologically +determined maximum possible rate of increase, data on +earliest possible age of female reproduction, highest possible +birth rate of female young, and longest possible female +reproductive life span were used for a, b, and n, respectively. +Calculated values, therefore, represent physiologically possible, +not ecologically possible, intrinsic rates of increase +(Hennemann, 1983, 1984; Hayssen, 1984; McNab, 1984b). +Values of n were derived from longevity records for captive +animals, and as these were all large values of similar duration +(14-16 years), they had very little effect on r<sub>max</sub>. All species +considered have one litter per year, and because their sex ratios +at birth are about 50:50, variation in b was due to differences +in litter size. Therefore, age of first reproduction and litter size +had the greatest effect on r<sub>max</sub>. Intrinsic rate of increase scales +to body mass (Fenchel, 1974), and we removed this effect by +comparing each calculated r<sub>max</sub> with the value expected (r<sub>maxe</sub>) +on the basis of body mass (Hennemann, 1983).</p> + +<a name="Comparison_of_Adaptive_Units"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Comparison of Adaptive Units</div> + +<p>Dimensionless numbers for each of the four variables used in +calculating composite scores were derived as follows. Ratios of +measured to predicted values were used for basal metabolism +(H<sub>br</sub>) and minimum wet thermal conductance (C<sub>mwr</sub>). Thermoregulatory +ability at low temperatures is closely related to +the ratio H<sub>br</sub>/C<sub>mwr</sub> (McNab, 1966). This ratio was used, +therefore, to gauge each species' cold tolerance. For D<sub>d</sub> we used +the ratio of food categories actually used by a species to the +total number of food categories taken by all species tested (D<sub>dr</sub>). +The ratio of calculated to expected intrinsic rates of natural +increase was used to derive r<sub>maxr</sub>. Composite scores were +calculated as</p> + +<table width="100%" summary="Eq. 3"> +<tr><td class="center">Composite score = [(H<sub>br</sub>/C<sub>mwr</sub>) + D<sub>dr</sub> + r<sub>maxr</sub>]/3</td><td class="text_rt">Eq. 3</td></tr> +</table> + +<p>The correlation between number of climates these species +occupy and their composite scores was tested by linear +regression.</p> + + +<br> +<a name="Results"></a> +<a name="Body_Mass"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption2">Results</div> +<div class="caption3">Body Mass</div> + +<p>According to monthly live-trapping records, the body mass +of free-ranging female raccoons increased from 3.6 ± 0.6 kg +during summer to 5.6 ± 0.8 kg in early winter, and the mass of +free-ranging males increased from 4.0 ± 0.5 to 6.7 ± 0.9 kg +during the same interval. These seasonal changes in body mass +were due to fluctuations in the amount of body fat and represent +a mechanism for storing energy during fall for use in winter. In +summer, captive and trapped male and captive female raccoons +had the same body mass (4.73 ± 0.61, 4.41 ± 0.70, and 4.67 +<span class="pagenum"><a name="Page_9" id="Page_9">[Pg 9]</a></span> +± 0.88 kg, respectively, <a href="#Table_2">Table 2</a>). Mass of captive females did +not change between seasons, whereas captive males were +heavier in winter than summer (p<0.005; <a href="#Table_2">Table 2</a>). This +seasonal change in mass of our captive males was of a much +smaller magnitude (0.6 kg) than that observed for wild males +(2.7 kg). During winter, captive males (5.34 ± 1.39 kg) were +heavier than captive females (4.49 ± 0.98 kg; p<0.005; <a href="#Table_2">Table +2</a>). Thus, our captive animals maintained a body mass +throughout the year that was intermediate to the range of values +found for wild raccoons in the same area.</p> + +<a name="Table_2"></a> +<div class="tab_cap"><span class="smcap">Table 2.</span>—Body mass in kg and basal metabolism <span class="nobreak">(mL O<sub>2</sub>·kg<sup>-0.75</sup>·h<sup>-1</sup>)</span> of <i>Procyon lotor</i> in summer and +winter (s.d. = standard deviation and n = number of observations).</div> +<br> +<table width="100%" class="center" cellpadding="4" summary="Body Mass and Basal Metabolism Comparison"> +<tr><th class="bt bb">Season and sex</th><th class="bt bl bb">Body mass, ± s.d.,</th><th class="bt bb">(n)</th><th class="bt bb">Basal metabolism, ± s.d.,</th><th class="bt bb">(n)</th></tr> +<tr><td class="text_lf">Summer</td><td colspan=4 class="bl"> </td></tr> +<tr><td class="text_lf"> Trapped male</td><td class="bl">4.41 ± 0.70</td><td>(52)</td><td>780 ± 112</td><td>(20)</td></tr> +<tr><td class="text_lf"> Captive male</td><td class="bl">4.73 ± 0.61</td><td>(22)</td><td>680 ± 102</td><td> (8)</td></tr> +<tr><td class="text_lf"> Captive female</td><td class="bl">4.67 ± 0.88</td><td>(41)</td><td>618 ± 92</td><td>(13)</td></tr> +<tr><td class="text_lf">Winter</td><td colspan=4 class="bl"> </td></tr> +<tr><td class="text_lf"> Captive male</td><td class="bl">5.34 ± 1.39</td><td>(31)</td><td>704 ± 81</td><td>(19)</td></tr> +<tr><td class="text_lf bb"> Captive female</td><td class="bl bb">4.49 ± 0.98</td><td class="bb">(42)</td><td class="bb">667 ± 139</td><td class="bb">(25)</td></tr> +</table> +<br> + +<a name="Basal_Metabolic_Rate_2"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Basal Metabolic Rate</div> + +<p>Within thermoneutrality, Ḣ<sub>b</sub> <span class="nobreak">(mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>)</span> was 0.54 ± 0.09 +for trapped males in summer, 0.46 ± 0.07 for captive males in +summer, 0.42 ± 0.07 for captive females in summer, 0.47 ± 0.06 +for captive males in winter, and 0.46 ± 0.10 for captive females +in winter (<a href="#Fig_2">Figures 2</a>,<a href="#Fig_3"> 3</a>). Ratios of these measured values to +those predicted by the Kleiber (1932, 1961:206) equation are +1.28, 1.12, 1.02, 1.17, and 1.09, respectively. To minimize the +effect of body size (Mellen, 1963) and to facilitate comparisons +between sexes and seasons and between captive and trapped +animals, basal metabolism also was calculated as a function of +metabolic body size <span class="nobreak">(mL O<sub>2</sub>·kg<sup>-0.75</sup>·h<sup>-1</sup>;</span> <a href="#Table_2">Table 2</a>). Based on this +analysis, trapped summer males had a higher basal metabolism +than captive males (p<0.025) or females (p<0.005) in either +season (<a href="#Table_2">Table 2</a>). There was no difference in basal metabolism +between captive males and females in either summer or winter, +and there was no seasonal difference in their basal metabolic +rates (<a href="#Table_2">Table 2</a>).</p> + +<a name="Minimum_Thermal_Conductance_2"></a> +<p><span class="pagenum"><a href="#toc">[↑ TOC]</a></span></p> +<div class="caption3">Minimum Thermal Conductance</div> + +<p>Minimum wet and dry thermal conductances were calculated +using Eqs. 4 and 5</p> + +<a name="Eq_4"></a> +<table width="100%" summary="Eq. 4"> +<tr><td class="center">C<sub>mw</sub> = Ḣ<sub>r</sub> / (T<sub>b</sub> - T<sub>a</sub>)</td><td class="text_rt">Eq. 4</td></tr> +</table> + +<table width="100%" summary="Eq. 5"> +<tr><td class="center">C<sub>md</sub> = (Ḣ<sub>r</sub> - Ė<sub>eq</sub>) / (T<sub>b</sub> - T<sub>a</sub>)</td><td class="text_rt">Eq. 5</td></tr> +</table> + +<p class="noidt"> +where C<sub>mw</sub> is wet and C<sub>md</sub> is dry conductance <span class="nobreak">(mL +O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>·°C<sup>-1</sup>);</span> Ḣ<sub>r</sub> is the lowest resting metabolic rate +measured at each temperature <span class="nobreak">(mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>);</span> +Ė<sub>eq</sub> is oxygen equivalent for heat lost by evaporation +[Ė<sub>eq</sub> = mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup> = Ė·λ/γ, where Ė is evaporative water loss +(mg·g<sup>-1</sup>·h<sup>-1</sup>), λ is heat of vaporization for water (2.43 J/mg), and +γ is heat equivalent for oxygen (20.097 J/mL)]; T<sub>b</sub> is body +temperature (°C); and T<sub>a</sub> is chamber air temperature (°C). Only +data from animals equipped with temperature-sensitive radio +transmitters were used for these calculations.</p> + +<a name="Table_3"></a> +<div class="tab_cap"><span class="smcap">Table 3.</span>—Minimum wet and dry thermal conductances <span class="nobreak">(mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>·°C<sup>-1</sup>)</span> of <i>Procyon lotor</i> in summer and +winter. Means of values were calculated from equations 3 and 4 (s.d. = standard deviation and n = number of +observations).</div> +<br> +<table width="100%" class="center" cellpadding="4" summary="Thermal Conductance"> +<tr><th rowspan=2 class="bt bb">Season and sex</th><th class="bt bl"> </th><th colspan=4 class="bt bb">Thermal conductance</th></tr> +<tr><th class="bl bb"> </th><th class="bb">Wet ± s.d.</th><th class="bb">(n)</th><th class="bb">Dry ± s.d.</th><th class="bb">(n)</th></tr> +<tr><td class="text_lf">Summer</td><td colspan=5 class="bl"> </td></tr> +<tr><td class="text_lf"> Captive, both sexes</td><td class="bl"> </td><td>0.0256 ± 0.0028</td><td>(18)</td><td>0.0246 ± 0.0019</td><td>(12)</td></tr> +<tr><td class="text_lf">Winter</td><td colspan=5 class="bl"> </td></tr> +<tr><td class="bb text_lf"> Captive, female</td><td class="bl bb"> </td><td class="bb">0.0172 ± 0.0023</td><td class="bb">(10)</td><td class="bb">0.0161 ± 0.0027</td><td class="bb"> (6)</td></tr> +</table> +<br> +<a name="Fig_2"></a> +<p><span class="pagenum"><a name="Page_10" id="Page_10">[Pg 10]</a></span></p> +<div class="center"> + <img src="images/fig_2.png" width="436" height="311" title="Relationship between oxygen consumption and chamber air temperature for raccoons in summer" alt="summer - oxygen consumpsion vs air temp"><br><br> + <div class="fig_cap"><span class="smcap">Figure 2.</span>—Relationship between oxygen consumption and chamber air temperature for raccoons in summer: captive females, open circles; captive males, closed circles; trapped males, open squares. Sloping lines represent regressions of oxygen consumption on chamber air temperature, and horizontal lines, basal metabolism.</div> +</div> + +<a name="Fig_3"></a> +<div class="center"> + <img src="images/fig_3.png" width="436" height="307" title="Relationship between oxygen consumption and chamber air temperature for raccoons in winter" alt="winter - oxygen consumpsion vs air temp"><br><br> + <div class="fig_cap"><span class="smcap">Figure 3.</span>—Relationship between oxygen consumption and chamber air temperature for raccoons in winter: captive females, open circles; captive males, closed circles. Solid sloping line represents regression of oxygen consumption on chamber air temperature for males and females, and the horizontal line, basal metabolism for males and females.</div> +</div> + +<p><span class="pagenum"><a name="Page_11" id="Page_11">[Pg 11]</a></span> +C<sub>mw</sub> was calculated for each season from metabolic +measurements made at all air temperatures below T<sub>lc</sub> (<a href="#Table_3">Table 3</a>). +Because evaporative water loss was not measured at temperatures +below freezing, C<sub>md</sub> was calculated only from metabolic +determinations made at air temperatures between T<sub>lc</sub> and 0°C. +There was no difference between males and females in summer +for either C<sub>mw</sub> or C<sub>md</sub> <span class="nobreak">(mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>·°C<sup>-1</sup>).</span> Data for each sex +were combined to give a summer average of 0.0256 ± 0.0028 +for C<sub>mw</sub>, and 0.0246 ± 0.0019 for C<sub>md</sub> (<a href="#Table_3">Table 3</a>). These summer +conductances were 49% higher (p<0.005) than those calculated +for winter females (0.0172 ± 0.0023, and 0.0161 ± 0.0027 for +C<sub>mw</sub> and C<sub>md</sub>, respectively; <a href="#Table_3">Table 3</a>). C<sub>mw</sub> and C<sub>md</sub> were not +different from each other in either summer or winter, which +indicated that in both seasons evaporative water loss contributed +very little to heat dissipation at temperatures below T<sub>n</sub>. +Comparisons of thermal conductances calculated on the basis +of metabolic body size (Mellen, 1963) gave the same results.</p> + +<a name="Evaporative_Water_Loss_2"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Evaporative Water Loss</div> + +<p>Evaporative water loss increased as chamber temperature +increased in both summer and winter (<a href="#Fig_4">Figures 4</a>,<a href="#Fig_5"> 5</a>). In summer, +the pattern of increase was different for females and males. +Polynomial regressions for trapped and captive males produced +equations that describe a concave relationship between T<sub>a</sub> and +evaporative water loss, whereas the equation for females +describes a sigmoid curve (<a href="#Table_4">Table 4</a>; <a href="#Fig_4">Figure 4</a>). For females, +water loss increased rapidly at temperatures above 25°C +(<a href="#Fig_4">Figure 4</a>). The intercepts and coefficients of the X, X<sup>2</sup>, and X<sup>3</sup> +terms of the polynomial regression equations (<a href="#Table_4">Table 4</a>) were +compared (<i>t</i>-tests) to determine if they differed from each other. +The coefficients in the equation for trapped males differed from +those for captive females in the X<sup>2</sup> (p<0.05) and X<sup>3</sup> (p<0.025) +terms. The intercept and coefficients of the equation for captive +males, however, were not different from those for either captive +females or trapped males. Although this lack of difference is +understandable in the case of trapped males, where the shape of +the two curves is similar (concave), it is not so clear for the +sigmoid curve of captive females (<a href="#Fig_4">Figure 4</a>). Perhaps the lack +of difference in this case is simply due to the small number of +observations available for captive males (n = 10; <a href="#Table_4">Table 4</a>). +Nonetheless, in summer at 35°C, both captive and trapped +males relied less on evaporative cooling than did captive +females (<a href="#Fig_4">Figure 4</a>).</p> + +<p>In winter, males and females had similar rates of evaporative +water loss across the full range of temperatures tested (<a href="#Fig_5">Figure +5</a>). Therefore, data for both sexes were combined. The intercept +and coefficients of this equation (<a href="#Table_4">Table 4</a>) did not differ from +those for summer females, but they did differ from those in the +regression for trapped males in the X<sup>2</sup> (p<0.05) and X<sup>3</sup> +(p<0.025) terms. As was the case for females in summer, +rates of water loss for winter animals increased most rapidly at +temperatures above 25°C (<a href="#Fig_5">Figure 5</a>).</p> + +<br> +<a name="Fig_4"></a> +<div class="center"> + <img src="images/fig_4.png" width="429" height="378" title="Relationship between evaporative water loss and chamber air temperature for raccoons in summer" alt="summer - evap water loss vs temp"><br><br> + <div class="fig_cap"><span class="smcap">Figure 4.</span>—Relationship between evaporative water loss and chamber air temperature for raccoons in summer: +captive females, open circles; captive males, closed circles; trapped males, open squares. Lines represent +polynomial regressions of evaporative water loss on chamber air temperature.</div> +</div> + +<a name="Fig_5"></a> +<span class="pagenum"><a name="Page_12" id="Page_12">[Pg 12]</a></span> +<div class="center"> + <img src="images/fig_5.png" width="382" height="333" title="Relationship between evaporative water loss and chamber air temperature for raccoons in winter" alt="winter - evap water loss vs temp"><br><br> + <div class="fig_cap"><span class="smcap">Figure 5.</span>—Relationship between evaporative water loss and chamber air temperature for raccoons in winter: captive females, open circles; captive males, closed circles. Lines represent polynomial regressions of evaporative water loss on chamber air temperature.</div> +</div> + +<a name="Table_4"></a> +<div class="tab_cap"><span class="smcap">Table 4.</span>—Polynomial regression equations describing evaporative water loss (mg·g<sup>-1</sup>·h<sup>-1</sup>) of <i>Procyon lotor</i> in +summer and winter (X = chamber temperature (°C), Y = evaporative water loss, n = number of observations, R<sup>2</sup> + = coefficient of determination, and SEE = standard error of estimate).</div> +<br> +<table width="100%" class="center" summary="Polnomial Regression Equations"> +<tr><th class="bt bb">Season and sex</th><th colspan=8 class="bt bl bb">Equation</th><th class="bt bb">(n)</th><th class="bt bb">R<sup>2</sup></th></tr> +<tr><td class="text_lf">Summer</td><td colspan=10 class="bl"> </td></tr> +<tr><td class="text_lf"> Trapped male</td><td class="bl">Y = </td><td class="text_lf">0.1899</td><td class="text_lf">+</td><td class="text_lf">0.0114 X</td><td class="text_lf">+ </td><td class="text_lf">0.0011 X<sup>2</sup></td><td class="text_lf">-</td><td class="text_lf">0.00002 X<sup>3</sup></td><td>(32)</td><td>0.86</td></tr> +<tr><td class="text_lf"> SEE</td><td class="bl"> </td><td class="text_lf">0.0885</td><td class="text_lf"> </td><td class="text_lf">0.0223</td><td class="text_lf"> </td><td class="text_lf">0.0015</td><td class="text_lf"> </td><td class="text_lf">0.00003</td><td> </td><td> </td></tr> +<tr><td class="text_lf"> </td><td class="bl" colspan=10> </td></tr> +<tr><td class="text_lf"> Captive male</td><td class="bl">Y = </td><td class="text_lf">0.2174</td><td class="text_lf">+</td><td class="text_lf">0.0192·X</td><td class="text_lf">+</td><td class="text_lf">0.0009·X<sup>2</sup></td><td class="text_lf">-</td><td class="text_lf">0.00003·X<sup>3</sup></td><td>(10)</td><td>0.73</td></tr> +<tr><td class="text_lf"> SEE</td><td class="bl"> </td><td class="text_lf">0.3983</td><td class="text_lf"> </td><td class="text_lf">0.0834</td><td class="text_lf"> </td><td class="text_lf">0.0048</td><td class="text_lf"> </td><td class="text_lf">0.00008</td><td> </td><td> </td></tr> +<tr><td class="text_lf"> </td><td class="bl" colspan=10> </td></tr> +<tr><td class="text_lf"> Captive female</td><td class="bl">Y = </td><td class="text_lf">0.0127</td><td class="text_lf">+</td><td class="text_lf">0.0943·X</td><td class="text_lf">- </td><td class="text_lf">0.0060·X<sup>2</sup></td><td class="text_lf">+</td><td class="text_lf">0.00013·X<sup>3</sup></td><td>(31)</td><td>0.64</td></tr> +<tr><td class="text_lf"> SEE</td><td class="bl"> </td><td class="text_lf">0.2218</td><td class="text_lf"> </td><td class="text_lf">0.0547</td><td class="text_lf"> </td><td class="text_lf">0.0036</td><td class="text_lf"> </td><td class="text_lf">0.00006</td><td> </td><td> </td></tr> +<tr><td class="text_lf"> </td><td class="bl" colspan=10> </td></tr> +<tr><td class="text_lf">Winter</td><td colspan=10 class="bl"> </td></tr> +<tr><td class="text_lf"> Captive, both sexes</td><td class="bl">Y = </td><td class="text_lf">0.1550</td><td class="text_lf">+</td><td class="text_lf">0.0426·X</td><td class="text_lf">-</td><td class="text_lf">0.0025·X<sup>2</sup></td><td class="text_lf">+</td><td class="text_lf">0.00006·X<sup>3</sup></td><td>(57)</td><td>0.80</td></tr> +<tr><td class="text_lf bb"> SEE</td><td class="bl bb"> </td><td class="text_lf bb">0.0734</td><td class="text_lf bb"> </td><td class="text_lf bb">0.0192</td><td class="bb text_lf"> </td><td class="text_lf bb">0.0013</td><td class="bb text_lf"> </td><td class="bb text_lf">0.00002</td><td class="bb"> </td><td class="bb"> </td></tr> +</table> +<br> + +<a name="Thermoregulation_at_Low_Temperatures"></a> +<a name="Body_Temperature_1"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Thermoregulation at Low Temperatures</div> +<div class="caption4">Body Temperature</div> + +<p>Body temperatures in <a href="#Fig_6">Figure 6</a> are those recorded during +metabolic measurements from animals equipped with surgically +implanted, temperature-sensitive radio transmitters. Each +point was recorded during the lowest level of oxygen +consumption at each T<sub>a</sub>. In both summer and winter, T<sub>b</sub>'s were +lowest during metabolic measurements at T<sub>a</sub>'s around T<sub>lc</sub>. At +T<sub>a</sub>'s below T<sub>lc</sub>, T<sub>b</sub>'s increased (<a href="#Fig_6">Figure 6</a>), which is an unusual +<span class="pagenum"><a name="Page_13" id="Page_13">[Pg 13]</a></span> +response. Under similar conditions, other procyonids either +maintain a nearly constant T<sub>b</sub> or allow it to fall slightly (Müller +and Kulzer, 1977; Chevillard-Hugot et al., 1980; Müller and +Rost, 1983; Chevalier, 1985). For our raccoons, confinement in +the metabolism chamber at low temperatures must have +stimulated a greater than necessary increase in metabolic rate +such that heat production exceeded heat loss, which caused T<sub>b</sub> +to become elevated.</p> + +<br> +<a name="Fig_6"></a> +<div class="center"> + <img src="images/fig_6.png" width="305" height="520" title="Relationship between body temperature and chamber air temperature" alt="body temp vs air temp"><br><br> + <div class="fig_cap"><span class="smcap">Figure 6.</span>—Relationship between body temperature and chamber air temperature in summer (panel A), and winter (panel B): captive females, open circles and solid lines; captive males, solid circles and dashed lines. Solid vertical lines represent lower critical temperatures.</div> +</div> + +<span class="pagenum"><a name="Page_14" id="Page_14">[Pg 14]</a></span> +<a name="Table_5"></a> +<div class="tab_cap"><span class="smcap">Table 5.</span>—Regression equations describing oxygen consumption <span class="nobreak">(mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>)</span> of <i>Procyon lotor</i> at temperatures below +their lower critical temperature (I = x-intercept (°C), n = number of observations, R<sup>2</sup> = coefficient of determination, SEE + = standard error of estimate for the y-intercept (a) and slope (b), X = chamber temperature (°C), and Y = oxygen consumption).</div> +<br> +<table width="100%" class="center" summary="Oxygen Consumption Regression Equations"> +<tr><th rowspan=2 class="bt bb">Season and sex</th><th rowspan=2 class="bt bl bb">Equation</th><th rowspan=2 class="bt bb">(n)</th><th rowspan=2 class="bt bb">R<sup>2</sup></th><th colspan=2 class="bt bb">SEE</th><th rowspan=2 class="bt bb">I</th></tr> +<tr><th class="bb">a</th><th class="bb">b</th></tr> +<tr><td class="text_lf">Summer</td><td colspan=6 class="bl"> </td></tr> +<tr><td class="text_lf"> Trapped male</td><td class="bl">Y = 1.09 - 0.0281·X</td><td>(30)</td><td>0.64</td><td>0.0353</td><td>0.0040</td><td>38.8</td></tr> +<tr><td class="text_lf"> Captive male</td><td class="bl">Y = 0.97 - 0.0258·X</td><td>(12)</td><td>0.91</td><td>0.0235</td><td>0.0025</td><td>37.6</td></tr> +<tr><td class="text_lf"> Captive female</td><td class="bl">Y = 1.04 - 0.0251·X</td><td>(29)</td><td>0.78</td><td>0.0288</td><td>0.0026</td><td>41.1</td></tr> +<tr><td class="text_lf">Winter</td><td colspan=6 class="bl"> </td></tr> +<tr><td class="text_lf bb"> Captive, both sexes</td><td class="bl bb">Y = 0.68 - 0.0193·X</td><td class="bb">(36)</td><td class="bb">0.68</td><td class="bb">0.0157</td><td class="bb">0.0023</td><td class="bb">35.2</td></tr> +</table> +<br> + +<a name="Summer_1"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Summer</div> + +<p>During summer, T<sub>lc</sub> for male raccoons was 20°C, whereas for +females it was 25°C (<a href="#Fig_2">Figure 2</a>). Regression equations calculated +to describe oxygen consumption at T<sub>a</sub>'s below T<sub>lc</sub> are +presented in <a href="#Table_5">Table 5</a>. For three groups of summer animals, +slopes of regressions are identical. This indicates that minimum +conductances of these three groups were equivalent. Intercepts +of these equations are different, which suggests a difference in +metabolic cost of thermoregulation between these groups +(<a href="#Fig_2">Figure 2</a>); captive males had a lower intercept than either +trapped males (p<0.005) or captive females (p<0.05), but there +was no difference in intercepts of captive females and trapped +males. These regression equations, therefore, also were derived +using values of oxygen consumption expressed in terms of +metabolic body mass (Mellen, 1963). Relationships between +intercepts of these equations are different than those for +regressions in <a href="#Table_5">Table 5</a>. Intercept for females was intermediate +to, and not different from, those of the two groups of males. +However, captive males still had a lower intercept than trapped +males (p<0.025). Thus, in summer, thermoregulatory metabolism +was less expensive for captive than for trapped males, and +in spite of a 5°C difference in their T<sub>lc</sub>'s (<a href="#Fig_2">Figure 2</a>), captive +males and females had similar thermoregulatory costs.</p> + +<p>Regression lines for three groups of animals in summer +extrapolate to zero metabolism at values equivalent to, or +greater than, normal T<sub>b</sub>; 38.8°C for trapped males, 37.6°C for +captive males, and 41.1°C for captive females (<a href="#Table_5">Table 5</a>). Thus, +all three groups had minimized thermal conductance at T<sub>a</sub>'s +below T<sub>lc</sub> (Scholander et al., 1950b; McNab, 1980b). Minimum +wet thermal conductance calculated for raccoons in summer +with <a href="#Eq_4">Eq. 4</a> (<a href="#Table_3">Table 3</a>) is numerically similar to these "slope" +values (<a href="#Table_5">Table 5</a>), and it was, therefore, considered to be the best +estimate of C<sub>mw</sub> for <i>Procyon lotor</i> during that season <span class="nobreak">(0.0256 +mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>·°C<sup>-1</sup>)</span>.</p> + +<a name="Winter_1"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Winter</div> + +<p>During winter T<sub>lc</sub> for both sexes decreased to 11°C (<a href="#Fig_3">Figure 3</a>). +Regression equations of thermoregulatory metabolism for +males and females in winter are not different from each other in +either slope or intercept. These data, therefore, were combined +into a single equation (<a href="#Table_5">Table 5</a>). Slope and intercept of this +equation are both lower (p<0.005 and p<0.05, respectively) +than those for summer animals (<a href="#Table_5">Table 5</a>). Identical results were +obtained from comparisons using regressions derived from +oxygen consumption expressed in terms of metabolic body +mass (Mellen, 1963). Thermoregulatory costs at any temperature +below 20°C were lower for winter than summer animals +(<a href="#Fig_2">Figures 2</a>,<a href="#Fig_3"> 3</a>).</p> + +<a name="Table_6"></a> +<div class="tab_cap"><span class="smcap">Table 6.</span>—Regression equations describing oxygen consumption <span class="nobreak">(mL +O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>)</span> of <i>Procyon lotor</i> at temperatures below their lower critical +temperature in winter (A = females with radio transmitters, B = females without +radio transmitters, C = males, I = x-intercept (°C), n = number of observations, +R<sup>2</sup> = coefficient of determination, X = chamber temperature (°C), and Y = +oxygen consumption).</div> +<br> +<table width="100%" class="center" summary="Oxygen COnsumpsion Regression Equations"> +<tr><th class="bt bb">Group</th><th class="bt bl bb">Equation</th><th class="bt bb">(n)</th><th class="bt bb">R<sup>2</sup></th><th class="bt bb">I</th></tr> +<tr><td>A</td><td class="bl">Y = 0.63 - 0.0158·X</td><td>(10)</td><td>0.66</td><td>40.1</td></tr> +<tr><td>B</td><td class="bl">Y = 0.72 - 0.0226·X</td><td>(11)</td><td>0.71</td><td>32.1</td></tr> +<tr><td class="bb">C</td><td class="bl bb">Y = 0.69 - 0.0200·X</td><td class="bb">(15)</td><td class="bb">0.79</td><td class="bb">34.7</td></tr> +</table> +<br> +<a name="Fig_7"></a> +<span class="pagenum"><a name="Page_15" id="Page_15">[Pg 15]</a></span> +<div class="center"> + <img src="images/fig_7.png" width="437" height="587" title="Relationship between body temperature and time of day" alt="body temp vs time of day"><br><br> + <div class="fig_cap"><span class="smcap">Figure 7.</span>—Relationship between body temperature and time of day at various months of the year: captive females, open circles; captive males, closed circles. Vertical cross-hatched areas represent civil twilight.</div> +</div> + +<p>The regression line for <i>Procyon lotor</i> in winter (<a href="#Table_5">Table 5</a>) +extrapolates to zero metabolism at 35.2°C, which is below +normal T<sub>b</sub> (<a href="#Fig_6">Figures 6</a>,<a href="#Fig_7"> 7</a>). This suggests that not all raccoons +measured in winter minimized thermoregulatory metabolism or +conductances at T<sub>a</sub>'s below T<sub>lc</sub> (Scholander et al., 1950b; +McNab, 1980b). To assess this possibility, data for these +animals were divided into three groups: (A) females with radio +transmitters, (B) females without radio transmitters, and (C) +males (<a href="#Table_6">Table 6</a>). Regression equations of metabolism below T<sub>lc</sub> +were derived for each group, and based on extrapolated T<sub>b</sub>'s at +zero metabolism, only the two females with implanted radio +transmitters (group A) minimized thermoregulatory metabolism +and conductance. Had animals in groups B and C also +minimized their thermal conductances, while retaining their +measured metabolic rates, their rates of heat production would +have been disproportionately higher than their rates of heat +loss. Equation 4 predicts that under these conditions their body +temperatures would have been elevated to 42.0°C and 40.4°C, +respectively. Thus, in order to avoid such a large increase in +body temperature, animals in groups B and C increased their +thermal conductances in preference to lowering their metabolic +<span class="pagenum"><a name="Page_16" id="Page_16">[Pg 16]</a></span> +rates. The regression equation of thermoregulatory metabolism +for all winter animals (<a href="#Table_5">Table 5</a>), therefore, overestimates +minimum metabolic cost of temperature regulation below T<sub>lc</sub>, +and its slope underestimates C<sub>mw</sub>. Consequently, the best +estimate of C<sub>mw</sub> for <i>Procyon lotor</i> in winter is the value +calculated for group A animals with <a href="#Eq_4">Eq. 4</a> (0.0172 mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>·°C<sup>-1</sup>; +<a href="#Table_3">Table 3</a>), and the minimum cost of thermoregulatory +metabolism at any T<sub>a</sub> below T<sub>lc</sub> is best estimated by +substituting this value into <a href="#Eq_4">Eq. 4</a> and solving for Ḣ<sub>r</sub>.</p> + +<a name="Thermoregulation_at_High_Temperatures"></a> +<a name="Body_Temperature_2"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Thermoregulation at High Temperatures</div> +<div class="caption4">Body Temperature</div> + +<p>In both summer and winter, T<sub>b</sub>'s increased during metabolic +measurements at T<sub>a</sub>'s above T<sub>lc</sub> (<a href="#Fig_6">Figure 6</a>). This response also +was seen during metabolic measurements conducted on other +procyonids (Müller and Kulzer, 1977; Chevillard-Hugot et al., +1980; Müller and Rost, 1983; Chevalier, 1985).</p> + +<a name="Summer_2"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Summer</div> + +<p>During summer our data suggested that the upper critical +temperature (T<sub>uc</sub>) was higher than 35°C. The lowest rates of +oxygen consumption at T<sub>a</sub> = 35°C occurred after 1.5 to 2.5 +hours of exposure to that temperature. Prolonged exposure to +this temperature in summer did not make animals restless, and +their rate of oxygen consumption was very stable throughout +each measurement. Body temperature responses at T<sub>a</sub> = 35°C +were recorded from two males and two females that had +implanted radio transmitters. With the exception of one male, +T<sub>b</sub>'s were maintained near 38°C (<a href="#Fig_6">Figure 6</a>). The one exception +(a male) maintained its T<sub>b</sub> at 39.3°C. At T<sub>a</sub> = 35°C, summer +males had rates of evaporative water loss that were lower than +those of summer females (<a href="#Fig_4">Figure 4</a>). At this temperature, males +dissipated 35% ± 6% and females 56% ± 18% of their metabolic +heat via evaporative water loss. Thus, at T<sub>a</sub> = 35°C, males must +have utilized modes of heat transfer other than evaporative +cooling (convective and conductive heat transfer) to a greater +extent than females.</p> + +<a name="Winter_2"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Winter</div> + +<p>Body temperature, evaporative water loss, and metabolic +data indicated that, in winter, T<sub>uc</sub> was very close to 35°C. In +winter, the lowest level of oxygen consumption was recorded +during the first hour after the chamber had reached T<sub>a</sub> = 35°C. +Unlike summer, animals became restless after the first hour at +35°C, at which point their oxygen consumption increased and +showed a high degree of variability. Body temperature +responses at 35°C were recorded from both females that had +implanted radio transmitters. In one case, T<sub>b</sub> rose from 37.9°C +at the end of the first hour to 40.5°C by the end of the second +hour, and as it did not show signs of leveling off, we terminated +the experiment. We exposed that same animal to T<sub>a</sub> = 35°C one +other time during winter. In that instance, its T<sub>b</sub> rose to 40.0°C +during the first 30 minutes and was maintained at that level for +three hours with no apparent distress. The other female elevated +its T<sub>b</sub> from 37.3°C to 39.0°C during the second hour at +T<sub>a</sub> = 35°C and maintained its T<sub>b</sub> at that level for +two hours. Thus, during winter, prolonged exposure to +T<sub>a</sub> = 35°C stimulated more of an increase in T<sub>b</sub> than it did in +summer. During winter, both males and females increased +evaporative water loss at T<sub>a</sub> = 35°C (<a href="#Fig_5">Figure 5</a>) but only to the +extent that they dissipated 35% ± 10% of their metabolic heat +production. Thus, even in winter, convective and conductive +heat transfers were still the most important modes of heat loss +at this temperature.</p> + +<a name="Daily_Cycle_of_Body_Temperature"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Daily Cycle of Body Temperature</div> + +<p>The daily cycle of raccoon T<sub>b</sub>'s during summer and winter +are presented in <a href="#Fig_7">Figure 7</a>. In general, T<sub>b</sub>'s showed a marked +circadian cycle in phase with photoperiod. T<sub>b</sub>'s rose above +38°C for several hours each night but remained below 38°C +during daytime. During summer, with the exception of one +female whose record was not typical (<a href="#Fig_7">Figure 7</a>), T<sub>b</sub>'s rose above +38°C shortly after sunset, whereas in winter T<sub>b</sub>'s did not rise +above 38°C until several hours after sunset. Once T<sub>b</sub> was +elevated it usually remained so until just before or after sunrise +(<a href="#Fig_7">Figure 7</a>). During summer, T<sub>b</sub> was above 38°C for 85% or +more of the time between sunset and sunrise (87% for the +female with the typical body temperature pattern, and 85% and +98% for males), whereas in winter it was elevated for only +47%-78% of the time between sunset and sunrise (47% and +61% for females, and 67% and 78% for males). During night, +T<sub>b</sub> would oscillate between 38°C and about 39°C, such that two +peak values occurred. These peak values presumably corresponded +to two periods of heightened nighttime activity. +During summer, one of these peaks occurred before and the +other after 24:00 hours, whereas in winter both peaks occurred +after 24:00 hours. With the exception of one female in winter +(<a href="#Fig_7">Figure 7</a>), the lowest T<sub>b</sub> of the day for both sexes was near +37°C, and this typically occurred during daytime (<a href="#Fig_7">Figure 7</a>).</p> + + + +<br> +<a name="Discussion"></a> +<a name="Basal_Metabolic_Rate_3"></a> +<a name="Background_1"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption2">Discussion</div> +<div class="caption3">Basal Metabolic Rate</div> +<div class="caption4">Background</div> + +<p>Basal metabolism represents the minimum energy required +by a mammal to maintain endothermy and basic homeostasis +(Lusk, 1917:141; Kleiber, 1932, 1961:251; Benedict, 1938:191-215; +Brody, 1945:59; Robbins, 1983:105-111). Mammals +with lower than predicted Ḣ<sub>b</sub> maintain endothermy and +enjoy its attendant advantages at a discount, whereas others, +with rates that are higher than predicted, pay a premium +<span class="pagenum"><a name="Page_17" id="Page_17">[Pg 17]</a></span> +(Calder, 1987). Such variation in Ḣ<sub>b</sub> appears to be tied to +ecological circumstances rather than taxonomic affinities +(Vogel, 1980; McNab, 1986a, 1988a, 1989), and depending on +environmental conditions, each rate provides an individual +with various advantages and limitations. During the course of +evolution, therefore, each species' Ḣ<sub>b</sub> evolves to provide it with +the best match between its energy requirements for continuous +endothermy, its food supply, and the thermal characteristics of +its environment.</p> + +<a name="Captive_versus_Wild_Raccoons"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Captive versus Wild Raccoons</div> + +<p>Male raccoons trapped in summer had higher Ḣ<sub>b</sub>'s than our +captive animals in any season (<a href="#Table_2">Table 2</a>). The higher rate of +metabolism of these trapped males could have been due to the +stress of captivity or to the fact that "wild" animals actually +may have higher metabolic rates than those that have adjusted +to captivity. If the latter is true, then our data for captive +animals underestimated the actual energy cost of maintenance +metabolism for <i>Procyon lotor</i> in the wild. At present, we have +no way of determining which of these alternatives is true.</p> + +<a name="Seasonal_Metabolism_of_Raccoons"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Seasonal Metabolism of Raccoons</div> + +<p>In some temperate-zone mammals, Ḣ<sub>b</sub> is elevated in winter, +which presumably increases their "cold-hardiness." Conversely, +lower summer metabolism is considered to be a +mechanism that reduces the potential for heat stress. Such +seasonal variation in Ḣ<sub>b</sub> has been found in several species: +collard peccary, <i>Tayassu tajacu</i> (Zervanos, 1975); antelope +jackrabbit, <i>Lepus alleni</i> (Hinds, 1977); desert cottontail, +<i>Sylvilagus audubonii</i> (Hinds, 1973); and, perhaps, cold-acclimatized +rat, <i>Rattus norvegicus</i> (Hart and Heroux, 1963). +Unlike these species, our captive raccoons showed no seasonal +variation in Ḣ<sub>b</sub> (<a href="#Table_2">Table 2</a>). Instead, raccoons achieved "cold-hardiness" +in winter and reduced their potential for heat stress +in summer with a large seasonal change in thermal conductance +(<a href="#Table_3">Table 3</a>).</p> + +<a name="Table_7"></a> +<div class="tab_cap"> +<span class="smcap">Table 7.</span>—Metabolic characteristics of several procyonid species. +</div> +<br> +<table width="100%" class="center" summary="Metabolic Characteristics"> +<tr><th class="bt bb center" rowspan=2>Species</th><th class="bt bl bb center" rowspan=2>Body<br>Mass<br>(g)</th><th class="bt"> </th><th class="bt bb center" colspan=2>Basal<sup><a name="FNanchor_A_6"></a><a href="#Footnote_A_6">[a]</a></sup><br>metabolism</th><th class="bt"> </th><th class="bt bb center" colspan=2>Minimum<sup><a name="FNanchor_B_7"></a><a href="#Footnote_B_7">[b]</a></sup><br>conductance</th><th class="bt"> </th><th class="bt bb center" colspan=2>T<sub>b</sub><sup><a name="FNanchor_C_8"></a><a href="#Footnote_C_8">[c]</a></sup></th><th class="bt"> </th><th class="bt bb center" colspan=2>T<sub>n</sub><sup><a name="FNanchor_D_9"></a><a href="#Footnote_D_9">[d]</a></sup></th><th class="bt bb" rowspan=2> </th><th class="bt bb center" rowspan=2>References</th></tr> +<tr><th class="bb"> </th><th class="bb center">Meas</th><th class="bb">H<sub>br</sub></th><th class="bb"> </th><th class="bb center"> Meas </th><th class="bb">C<sub>mwr</sub></th><th class="bb"> </th><th class="bb center">α</th><th class="bb">ρ</th><th class="bb"> </th><th class="bb center">T<sub>lc</sub></th><th class="bb">T<sub>uc</sub></th></tr> +<tr><td class="text_lf"><i>Bassariscus astutus</i></td><td class="bl">865</td><td> </td><td>0.43</td><td>0.68</td><td> </td><td>0.0288<sup><a name="FNanchor_E_10"></a><a href="#Footnote_E_10">[e]</a></sup></td><td> 0.85</td><td> </td><td> 37.6 </td><td>23</td><td> </td><td>35.5</td><td colspan=2> </td><td class="text_lf">Chevalier (1985)</td></tr> +<tr><td class="text_lf"><i>Procyon cancrivorus</i></td><td class="bl">1160</td><td> </td><td>0.40</td><td>0.69</td><td> </td><td>0.0368<sup><a href="#Footnote_E_10">[e]</a></sup></td><td>1.25</td><td> </td><td> </td><td> </td><td> </td><td>26</td><td colspan=2> </td><td class="text_lf">Scholander et al. (1950b, c)</td></tr> +<tr><td class="text_lf"><i>Potos flavus</i></td><td class="bl">2030</td><td> </td><td>0.36</td><td>0.51</td><td> </td><td> </td><td> </td><td> </td><td> </td><td colspan=5> </td><td class="text_lf">McNab (1978a)</td></tr> + +<tr><td class="text_lf"><i>Potos flavus</i></td><td class="bl">2400</td><td> </td><td>0.32</td><td>0.65</td><td> </td><td> </td><td> </td><td> </td><td>38.1</td><td>36.0</td><td> </td><td>23</td><td>30</td><td> </td><td class="text_lf">Müller and Kulzer (1977)</td></tr> +<tr><td class="text_lf"><i>Potos flavus</i></td><td class="bl">2600</td><td> </td><td>0.34</td><td>0.71</td><td> </td><td>0.0200<sup><a name="FNanchor_F_11"></a><a href="#Footnote_F_11">[f]</a></sup></td><td>1.02</td><td colspan=4> </td><td>23</td><td>33</td><td> </td><td class="text_lf">Müller and Rost (1983)</tr> +<tr><td class="text_lf"><i>Nasua nasua</i></td><td class="bl">3850</td><td> </td><td>0.26</td><td>0.60</td><td> </td><td>0.0200<sup><a href="#Footnote_F_11">[f]</a></sup></td><td>1.24</td><td> </td><td>38.3</td><td>36.4</td><td> </td><td>25</td><td>33</td><td> </td><td class="text_lf">Chevillard-Hugot et al. (1980)</td></tr> +<tr><td class="text_lf"><i>Nasua nasua</i></td><td class="bl">4847</td><td> </td><td>0.33</td><td>0.79</td><td> </td><td>0.0238<sup><a href="#Footnote_E_10">[e]</a></sup></td><td>1.65</td><td> </td><td>39.1</td><td>37.9</td><td> </td><td>30</td><td>35</td><td> </td><td class="text_lf">Mugaas et al. (in prep.)</td></tr> +<tr><td class="text_lf"><i>Nasua narica</i></td><td class="bl">5554</td><td> </td><td>0.25</td><td>0.62</td><td> </td><td>0.0208<sup><a href="#Footnote_E_10">[e]</a></sup></td><td>1.55</td><td> </td><td>38.9</td><td>37.4</td><td> </td><td>25</td><td>35</td><td> </td></tr> +<tr><td class="text_lf"><i>Nasua narica</i></td><td class="bl">4150</td><td> </td><td>0.42</td><td>1.20</td><td> </td><td>0.0341<sup><a href="#Footnote_E_10">[e]</a></sup></td><td>2.20</td><td colspan=7> </td><td class="text_lf">Scholander et al. (1950b, c)</td></tr> +<tr><td> </td><td class="bl" colspan=5> </td><td>0.0224<sup><a name="FNanchor_G_12"></a><a href="#Footnote_G_12">[g]</a></sup></td><td>1.45</td><td> </td></tr> +<tr><td class="text_lf"><i>Procyon lotor</i></td><td class="bl" colspan=14> </td><td class="text_lf">This study</td></tr> +<tr><td class="text_lf"><i>Summer</i></td><td class="bl" colspan=10> </td></tr> +<tr><td class="text_lf ind2em">Trapped male</td><td class="bl">4400</td><td> </td><td>0.54</td><td>1.28</td><td colspan=6> </td><td> </td><td>20</td><td colspan=3> </td></tr> +<tr><td class="text_lf ind2em">Captive male</td><td class="bl">4790</td><td> </td><td>0.46</td><td>1.07</td><td> </td><td>0.0256<sup><a href="#Footnote_F_11">[f]</a></sup></td><td>1.77</td><td> </td><td>38.4</td><td>37.5</td><td> </td><td>20</td><td colspan=3> </td></tr> +<tr><td class="text_lf ind2em">Captive female</td><td class="bl">4670</td><td> </td><td>0.42</td><td>1.02</td><td> </td><td>0.0256<sup><a href="#Footnote_F_11">[f]</a></sup></td><td>1.79</td><td> </td><td>38.2</td><td>37.6</td><td> </td><td>25</td><td colspan=3> </td></tr> +<tr><td class="text_lf"><i>Winter</i></td><td class="bl" colspan=15> </td></tr> +<tr><td class="text_lf ind2em">Captive male</td><td class="bl">5340</td><td> </td><td>0.47</td><td>1.17</td><td> </td><td colspan=3> </td><td>38.6</td><td>38.6</td><td> </td><td>11</td><td colspan=3> </td></tr> +<tr><td class="bb text_lf ind2em">Captive female</td><td class="bl bb">4490</td><td class="bb"> </td><td class="bb">0.46</td><td class="bb">1.10</td><td class="bb"> </td><td class="bb">0.0172<sup><a href="#Footnote_F_11">[f]</a></sup></td><td class="bb">1.15</td><td class="bb"> </td><td class="bb">38.3</td><td class="bb">37.3</td><td class="bb"> </td><td class="bb">11</td><td class="bb" colspan=3> </td></tr> +</table> +<br> +<div class="footnote"> +<a name="Footnote_A_6" id="Footnote_A_6"></a><a href="#FNanchor_A_6"><span class="label">[a]</span></a> +Meas is measured basal metabolism <span class="nobreak">(mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>).</span> H<sub>br</sub> is the ratio of measured to predicted basal metabolism where the predicted value is calculated from Ḣ<sub>b</sub> + = 3.42·m<sup>-.25</sup> (Kleiber, 1932, 1961:206) and m is body mass in grams.<br> +<br> + +<a name="Footnote_B_7" id="Footnote_B_7"></a><a href="#FNanchor_B_7"><span class="label">[b]</span></a> Meas is measured minimum thermal conductance <span class="nobreak">(mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>·°C<sup>-1</sup>).</span> C<sub>mwr</sub> is the ratio of measured to predicted minimum thermal conductance where the predicted value is calculated from C<sub>m</sub> = 1.0·m<sup>-0.5</sup> (McNab and Morrison, 1963; Herreid and Kessel, 1967), and m is body mass in grams.<br> +<br> + +<a name="Footnote_C_8" id="Footnote_C_8"></a><a href="#FNanchor_C_8"><span class="label">[c]</span></a> T<sub>b</sub> is body temperature during the active (α) and rest (ρ) phases of the daily cycle (°C).<br> +<br> + +<a name="Footnote_D_9" id="Footnote_D_9"></a><a href="#FNanchor_D_9"><span class="label">[d]</span></a> T<sub>n</sub> is the thermoneutral zone as defined by the lower (T<sub>lc</sub>) and upper (T<sub>uc</sub>) critical temperatures (°C).<br> +<br> + +<a name="Footnote_E_10" id="Footnote_E_10"></a><a href="#FNanchor_E_10"><span class="label">[e]</span></a> Conductance calculated as the slope of the line describing oxygen consumption at temperatures below the lower critical temperature.<br> +<br> + +<a name="Footnote_F_11" id="Footnote_F_11"></a><a href="#FNanchor_F_11"><span class="label">[f]</span></a> Conductance calculated from C<sub>mw</sub> = Ḣ<sub>r</sub>/(T<sub>b</sub> - T<sub>a</sub>), where Ḣ<sub>r</sub> is resting metabolic rate at temperatures below T<sub>lc</sub>, and other symbols are as described elsewhere.<br> +<br> + +<a name="Footnote_G_12" id="Footnote_G_12"></a><a href="#FNanchor_G_12"><span class="label">[g]</span></a> Inactive-phase thermal conductance: estimated from Scholander et al. (1950b), assuming that active-phase thermal conductance is 52% higher than values determined during the inactive phase (Aschoff, 1981).<br> +<br> +</div> + + +<a name="Comparison"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Comparison of Procyon lotor with Other Procyonids</div> + +<p><i>Procyon lotor</i> has a much higher mass-specific Ḣ<sub>b</sub> than other +procyonids (<a href="#Table_7">Table 7</a>). To quantify the magnitude of this +difference, we compared the measured value for <i>Procyon lotor</i> +<span class="pagenum"><a name="Page_18" id="Page_18">[Pg 18]</a></span> +with one calculated for it from a mass-specific least-squares +regression equation (<a href="#Eq_6">Eq. 6</a>; R<sup>2</sup> = 0.78) derived from data for +those procyonids with lower than predicted Ḣ<sub>b</sub>: <i>Potos flavus</i>, +<i>Procyon cancrivorus</i>, <i>Nasua nasua</i>, <i>Nasua narica</i>, and +<i>Bassariscus astutus</i> (<a href="#Table_7">Table 7</a>).</p> + +<a name="Eq_6"></a> +<table width="100%" summary="Eq. 6"> +<tr><td class="center">Ḣ<sub>b</sub> = 2.39·m<sup>-0.25</sup></td><td class="text_rt">Eq. 6</td></tr> +</table> + +<p>Ḣ<sub>b</sub> in Eq. 6 is basal metabolism <span class="nobreak">(mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>)</span> and m is body +mass (g). Measured values of Ḣ<sub>b</sub> for <i>Procyon lotor</i> were 1.45 to +1.86 times greater than those predicted for it by Eq. 6 (<a href="#Table_8">Table 8</a>).</p> + +<a name="Table_8"></a> +<div class="tab_cap"><span class="smcap">Table 8.</span>—Basal metabolism <span class="nobreak">(mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>)</span> of <i>Procyon lotor</i> as predicted by +<a href="#Eq_6">Eq. 6</a> (Ḣ<sub>b</sub> = 2.39·m<sup>-0.25</sup>). Body masses, used to calculate predicted values, and +measured values were taken from <a href="#Table_7">Table 7</a>.</div> +<br> +<div class="center"> +<table width="60%" class="center" summary="Basal Metabolism"> +<tr><th class="bt bb">Season and sex</th><th class="bt bl bb">Predicted</th><th class="bt bb"> </th><th class="bt bb">Measured/Predicted</th></tr> +<tr><td class="text_lf">Summer</td><td colspan=3 class="bl"> </td></tr> +<tr><td class="text_lf"> Trapped male</td><td class="bl">0.29</td><td> </td><td>1.86</td></tr> +<tr><td class="text_lf"> Captive male</td><td class="bl">0.29</td><td> </td><td>1.59</td></tr> +<tr><td class="text_lf"> Captive female</td><td class="bl">0.29</td><td> </td><td>1.45</td></tr> +<tr><td class="text_lf">Winter</td><td colspan=3 class="bl"> </td></tr> +<tr><td class="text_lf"> Captive male</td><td class="bl">0.28</td><td> </td><td>1.68</td></tr> +<tr><td class="text_lf bb"> Captive female</td><td class="bl bb">0.29</td><td class="bb"> </td><td class="bb">1.59</td></tr> +</table> +</div> +<br> + +<a name="Influence_of_Diet"></a> +<a name="Background_2"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Influence of Diet on Basal Metabolism</div> + +<p><span class="smcap">Background.</span>—With respect to Ḣ<sub>b</sub>, McNab (1986a:1) +maintains that "the influence of climate is confounded with the +influence of food habits," and that departures from the Kleiber +(1961) "norm" are best correlated with diet. Although this does +appear to be the case for diet specialists, the analysis is not so +clear-cut for omnivorous species (McNab, 1986a). His analysis +also indicates that an animal's "behavior" (i.e., whether it is +terrestrial, arboreal, subterranean, aquatic, etc.), secondarily +modifies the influence of food habits on Ḣ<sub>b</sub>. For example, +terrestrial frugivores have Ḣ<sub>b</sub>'s that are very near predicted +values, whereas arboreal frugivores have rates that are much +lower than predicted (McNab, 1986a).</p> + +<a name="Table_9"></a> +<div class="tab_cap"><span class="smcap">Table 9.</span>—Food habits of some Procyonids. References for foods were as follows: <i>Potos flavus</i>, <i>Procyon cancrivorus</i>, and <i>Nasua nasua</i> taken from Bisbal (1986); <i>Nasua narica</i> taken from Kaufmann (1962:182-198); <i>Bassariscus astutus</i> taken from Martin et al. (1951), Taylor (1954), Wood (1954), Toweill and Teer (1977), and Trapp (1978); <i>Procyon lotor</i> taken from Hamilton (1936), Stuewer (1943:218-220), Stains (1956:39-51), and Greenwood (1981). Symbols represent either qualitative (#) or quantitative (+, †) assessments of feeding habits: # indicates that the animal was observed eating the food; + and † represent volume and frequency, respectively, of food utilization. No attempt was made to account for seasonal variation in the use of these foods.</div> +<br> +<table width="70%" summary="key"> +<tr><td>+</td><td><20% by volume when found.</td><td>†</td><td>1%-19% frequency of occurrence.</td></tr> +<tr><td>++</td><td>>20% by volume when found.</td><td>††</td><td>20%-50% frequency of occurrence.</td></tr> +<tr><td colspan=2> </td><td>†††</td><td>>50% frequency of occurrence.</td></tr> +</table> +<br> + +<table width="100%" class="center" summary="Prey of Procyonids"> +<tr><th class="text_lf bt br bb">Food</th><th colspan=2 class="bt bb">Potos flavus</th><th colspan=2 class="bt bb">Procyon cancrivorus</th><th colspan=2 class="bt bb">Nasua nasua</th><th colspan=2 class="bt bb">Nasua narica</th><th colspan=2 class="bt bb">Bassariscus</th><th colspan=2 class="bt bb">Procyon lotor</th></tr> +<tr><td class="text_lf br">Mammalia</td><td> </td><td> </td><td> </td><td> </td><td>+</td><td>†</td><td> #</td><td> </td><td>++</td><td>†††</td><td>++</td><td>††</td></tr> +<tr><td class="text_lf br">Aves</td><td> </td><td> </td><td> </td><td> </td><td> </td><td> </td><td> </td><td> </td><td>++</td><td>†</td><td>+</td><td>††</td></tr> +<tr><td class="text_lf br">Birds' eggs</td><td> </td><td colspan=10> </td><td>†††</td></tr> +<tr><td class="text_lf br">Reptilia</td><td> </td><td> </td><td>+</td><td>†</td><td>+</td><td>†††</td><td> #</td><td> </td><td>+</td><td>†</td><td>+</td><td>†</td></tr> +<tr><td class="text_lf br">Amphibia</td><td> </td><td> </td><td>+</td><td>†</td><td> </td><td> </td><td> </td><td> </td><td> </td><td> </td><td>+</td><td>†</td></tr> +<tr><td class="text_lf br">Pices</td><td> </td><td> </td><td>++</td><td>††</td><td> </td><td> </td><td> </td><td> </td><td> </td><td> </td><td>++</td><td>††</td></tr> +<tr><td class="text_lf br">Insecta</td><td>++</td><td>†</td><td>+</td><td>†††</td><td>++</td><td>†††</td><td> #</td><td> </td><td>+</td><td>††</td><td>++</td><td>††</td></tr> +<tr><td class="text_lf br">Arachnida</td><td> </td><td> </td><td> </td><td> </td><td>++</td><td>†††</td><td> #</td><td> </td><td>+</td><td>†</td><td>+</td><td>†</td></tr> +<tr><td class="text_lf br">Chilopoda</td><td> </td><td> </td><td> </td><td> </td><td>++</td><td>†††</td><td colspan=6> </td></tr> +<tr><td class="text_lf br">Diplopoda</td><td colspan=6> </td><td> #</td><td> </td><td> </td><td> </td><td>+</td><td>†</td></tr> +<tr><td class="text_lf br">Crustacea</td><td> </td><td> </td><td>++</td><td>†††</td><td> </td><td> </td><td> #</td><td> </td><td> </td><td> </td><td>++</td><td>†††</td></tr> +<tr><td class="text_lf br">Mollusca</td><td> </td><td> </td><td>+</td><td>††</td><td> </td><td> </td><td> #</td><td> </td><td> </td><td> </td><td>+</td><td>††</td></tr> +<tr><td class="text_lf br">Annelida</td><td colspan=6> </td><td> #</td><td colspan=3> </td><td>+</td><td>†</td></tr> +<tr><td class="text_lf br">Nuts</td><td colspan=10> </td><td>++</td><td>††</td></tr> +<tr><td class="text_lf br">Grains</td><td colspan=10> </td><td>++</td><td>††</td></tr> +<tr><td class="text_lf br">Buds</td><td colspan=10> </td><td>+</td><td>†</td></tr> +<tr><td class="text_lf br">Fruit</td><td>++</td><td>†††</td><td> </td><td> </td><td>++</td><td> </td><td> #</td><td> </td><td> </td><td>††</td><td>++</td><td>†††</td></tr> +<tr><td class="text_lf br">Leaves</td><td colspan=10> </td><td>+</td><td>†</td></tr> +<tr><td class="text_lf br bb">Grass</td><td class="bb" colspan=10> </td><td class="bb">+</td><td class="bb"> †</td></tr> +</table> +<br> + +<a name="Food_Habits_of_Procyonids"></a> +<p><span class="smcap">Food Habits of Procyonids.</span>—Food habits of six procyonids +for which metabolic data are available are presented in +<a href="#Table_9">Table 9</a>. All six species clearly have mixed diets. Compared to +other species, <i>Procyon lotor</i> is highly catholic in its diet, taking +food from almost twice as many categories as <i>Nasua narica</i>, +three times as many as <i>Procyon cancrivorus</i>, <i>Nasua nasua</i>, and +<i>Bassariscus astutus</i>, and nine times as many as <i>Potos flavus</i>.</p> + +<p><span class="pagenum"><a name="Page_19" id="Page_19">[Pg 19]</a></span> +For those species for which food habit data are quantified, we +used Eisenberg's (1981:247-251) substrate/feeding matrix +method, where "substrate" is analogous to McNab's (1986a) +"behavior," to construct the following feeding categories that +are based on the major food groups utilized by each species +(<a href="#Table_9">Table 9</a>).</p> + +<div class="blockquot"><p class="noidt"> +1. <i>Potos flavus:</i> (1) arboreal/frugivore, insectivore.<br> +2. <i>Procyon cancrivorus:</i> (1) semiaquatic/crustacivore, molluscivore, insectivore, piscivore, carnivore.<br> +3. <i>Nasua nasua:</i> (1) terrestrial/insectivore, arachnidivore, carnivore, frugivore.<br> +4. <i>Bassariscus astutus:</i> (1) terrestrial/carnivore, insectivore, frugivore.<br> +5. <i>Procyon lotor:</i> (1) terrestrial/carnivore, granivore, frugivore, insectivore; and (2) semiaquatic/crustacivore, molluscivore, insectivore, piscivore, carnivore. +</p></div> + +<a name="Food_Habits_and_Basal_Metabolism"></a> +<p><span class="smcap">Food Habits and Basal Metabolism.</span>—The most important +foods in the diet of <i>Procyon lotor</i> are vertebrates, nuts, +seeds, and fruits (<a href="#Table_9">Table 9</a>). These are the same foods that are +eaten by those dietary specialists that have Ḣ<sub>b</sub>'s equivalent to, +or higher than, values predicted for them by the Kleiber +equation (McNab, 1986a). The most important foods in the +diets of <i>Potos flavus</i>, <i>Procyon cancrivorus</i>, and <i>Nasua nasua</i> +are invertebrates and fruit (<a href="#Table_9">Table 9</a>), and these foods are eaten +by dietary specialists that have lower than predicted Ḣ<sub>b</sub>'s +(McNab, 1986a). Major foods in the diet of <i>Bassariscus astutus</i> +are terrestrial vertebrates, insects, and fruit (<a href="#Table_9">Table 9</a>). Dietary +specialists that eat terrestrial vertebrates have higher than +predicted Ḣ<sub>b</sub>'s, whereas those that feed on insects have Ḣ<sub>b</sub>'s +that are lower than predicted (McNab, 1986a). Year-round +utilization of vertebrates by <i>Bassariscus astutus</i> suggests that it +also should have a metabolic rate that is equivalent to or higher +than predicted, rather than lower (McNab, 1986a). However, +perhaps year-round inclusion of insects in its diet (Martin et al., +1951; Taylor, 1954; Wood, 1954; Toweill and Teer, 1977; +Trapp, 1978), plus water-and energy-conserving advantages of +a low metabolic rate, each exert a stronger selective influence +on Ḣ<sub>b</sub> than do vertebrates in its diet.</p> + +<a name="Summary_1"></a> +<p><span class="smcap">Summary.</span>—The basal metabolic rate of these procyonids +does appear to be influenced by diet. But, it is apparent from +this family's evolutionary history and tropical origins that +climate also has had a profound influence on its member's +metabolism. The history of the family and the data presented +here (<a href="#Table_7">Table 7</a>) suggest that lower than predicted Ḣ<sub>b</sub> is a feature +that evolved very early as the primary metabolic adjustment to +a tropical climate. From this perspective, it could be argued that +climate would have been the major selective force determining +Ḣ<sub>b</sub>, whereas food habits would have had a secondary influence.</p> + +<a name="Basal_Metabolism_1"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<a name="Background_3"></a> +<div class="caption4">Basal Metabolism and Intrinsic Rate of Natural Increase</div> + +<p><span class="smcap">Background.</span>—McNab (1980a) suggested that if food is +not restricted during an animal's reproductive period, the factor +that will limit growth and reproduction will be the rate at which +energy can be used in growth and development. Under these +conditions, an increase in Ḣ<sub>b</sub> would actually increase r<sub>max</sub> +because it would provide a higher rate of biosynthesis, a faster +growth rate, and a shorter generation time. Hennemann (1983) +tested McNab's (1980a) premise and found a significant +correlation between r<sub>max</sub> and metabolic rate, independent of +body size, for 44 mammal species. A low correlation +coefficient for this relationship, however, indicated to him +(Hennemann, 1983) that factors such as (1) food supply, (2) +thermal characteristics of the environment, and (3) brain size +also contribute toward shaping a species' reproductive potential, +particularly when these factors strongly influence rates of +biosynthesis or growth or for some reason alter generation time. +Results of our estimates of r<sub>max</sub> for procyonids are presented in +<a href="#Table_10">Table 10</a>.</p> + +<a name="Procyon_lotor_1"></a> +<p><i>Procyon lotor.</i>—This species had the highest Ḣ<sub>b</sub> and D<sub>d</sub>, and +also had the highest r<sub>max</sub> (1.34; <a href="#Table_10">Table 10</a>). Such a high r<sub>max</sub> may +infer that this trait evolved under conditions where food and +temperature were not limiting to reproduction. Under these +conditions selection could have favored those reproductive +characteristics sensitive to a higher Ḣ<sub>b</sub> (biosynthesis, growth, +and generation time; McNab, 1980a). <i>Procyon lotor</i>'s high +reproductive potential is due to its early age of first female +reproduction and its large litter size, characteristics that may +reflect metabolically driven increases in both biosynthesis and +growth.</p> + +<a name="Bassariscus_astutus_1"></a> +<p><i>Bassariscus astutus.</i>—This species has a low Ḣ<sub>b</sub> but an r<sub>max</sub> +that was 124% of expected (<a href="#Table_10">Table 10</a>). This suggests that r<sub>max</sub> +evolved under conditions where food and temperature were not +limiting to reproduction. Reduced litter size should restrict this +species' reproductive potential and may be a reflection of its +low Ḣ<sub>b</sub>. The factor that is responsible for increasing its +reproductive potential, however, is its early age of first female +reproduction. <i>Bassariscus astutus</i> is the smallest of these +procyonids, and even though it has a low Ḣ<sub>b</sub>, its small mass +may contribute to its ability to reach adult size and sexual +maturity in its first year. The high quality of its diet (a high +proportion of small vertebrates; <a href="#Table_9">Table 9</a>) also may be a factor +that is permissive to early female reproduction. Thus, small +body size and diet may be factors that have allowed this species +to evolve a higher than expected reproductive potential in spite +of its low Ḣ<sub>b</sub>.</p> + +<a name="Nasua_narica_1"></a> +<p><i>Nasua narica.</i>—This species is one of the largest procyonids +(<a href="#Table_7">Table 7</a>), and it possesses characteristics that should limit its +reproductive potential: lower than predicted Ḣ<sub>b</sub> (<a href="#Table_7">Table 7</a>), a +relatively low-quality diet (Kaufmann, 1962:182-198; <a href="#Table_9">Table +9</a>), and delayed time of first reproduction (<a href="#Table_10">Table 10</a>). In spite of +this, <i>Nasua narica</i> has a higher than expected r<sub>max</sub> (111% of +predicted; <a href="#Table_10">Table 10</a>). The life history feature that enhances +<i>Nasua narica</i>'s reproductive potential, and increases r<sub>max</sub> +beyond expected, is its large litter size. In this species females +live in bands. Each year just before their young are born these +bands break up, and each female seeks out a den for herself and +<span class="pagenum"><a name="Page_20" id="Page_20">[Pg 20]</a></span> +her litter. Once the young are able to leave the den +(approximately five weeks), bands reform. In this situation, +females not only care for their own young but also for those of +other females in the band (Kaufmann, 1962:157-159, 1982, +1987; Russell, 1983). This social structure may contribute to +this species' ability to produce large litters and in this way +increase its reproductive potential.</p> + +<a name="Table_10"></a> +<div class="tab_cap"><span class="smcap">Table 10.</span>—Intrinsic rate of natural increase (r<sub>max</sub>) of several procyonids. (a = potential age of females producing first young; b = potential annual birth rate of female young (= average litter size/2; average litter size was calculated from the published range of litter sizes for each species); n = potential age of females producing their final young; r<sub>maxe</sub> = intrinsic rate of natural increase expected from body mass (Hennemann, 1983); r<sub>maxr</sub> = ratio of calculated to expected intrinsic rate of natural increase (r<sub>max</sub>/r<sub>maxe</sub>).)</div> +<br> +<table width="100%" class="center" summary="Intrinsic rate of natural increase"> +<tr><th class="bt bb">Species</th><th class="bt bl bb">Body<br>mass (g)</th><th class="bt bb"> a </th><th class="bt bb"> b </th><th class="bt bb"> n </th><th class="bt bb"> r<sub>max</sub> </th> +<th class="bt bb">r<sub>maxe</sub><a name="FNanchor_A_13" id="FNanchor_A_13"></a><a href="#Footnote_A_13" class="fnanchor">[a]</a></th> +<th class="bt bb">r<sub>maxr</sub><a name="FNanchor_B_14" id="FNanchor_B_14"></a><a href="#Footnote_B_14" class="fnanchor">[b]</a></th><th class="bt bb">References</th></tr> + +<tr><td class="text_lf vtop"><i>Procyon lotor</i></td><td class="bl vtop">4940</td><td class="vtop">0.83</td><td class="vtop">2.25</td><td class="vtop">16</td><td class="vtop">1.34</td><td class="vtop"> 0.53 </td><td class="vtop"> 2.52 </td><td class="text_lf">Dunn and Chapman (1983); Eisenberg (1981:489); Kaufmann (1987); Lotze and Anderson (1979); Nowak and Paradiso (1983:981); Sanderson(1987); Stains (1956:28-31); This study</td></tr> +<tr><td class="text_lf vtop"><i>Bassariscus astutus</i></td><td class="bl vtop">900</td><td class="vtop">0.83</td><td class="vtop">1.50</td><td class="vtop">14</td><td class="vtop">1.02</td><td class="vtop">0.82</td><td class="vtop">1.24</td><td class="text_lf">Kaufmann (1982, 1987); Nowak and Paradiso(1983:979, 980); Poglayen-Neuwall and Poglayen-Neuwall (1980); Poglayen-Neuwall and Toweill (1988); Russell (1983)</td></tr> +<tr><td class="text_lf vtop"><i>Nasua narica</i></td><td class="bl vtop">3900</td><td class="vtop">2.50</td><td class="vtop">2.25</td><td class="vtop">14</td><td class="vtop">0.62</td><td class="vtop">0.56</td><td class="vtop">1.11</td><td class="text_lf">Kaufmann (1982, 1987); Nowak and Paradiso (1983:983); Sanderson (1983)</td></tr> +<tr><td class="text_lf vtop"><i>Nasua nasua</i></td><td class="bl vtop">3850</td><td colspan=6> </td><td class="text_lf">Chevillard-Hugot et al. (1980)</td></tr> +<tr><td class="text_lf vtop"><i>Procyon cancrivorus</i></td><td class="bl vtop">1160</td><td class="vtop">0.83</td><td class="vtop">1.50</td><td class="vtop">15</td><td class="vtop2"> 1.02<a name="FNanchor_C_15" id="FNanchor_C_15"></a><a href="#Footnote_C_15" class="fnanchor">[c]</a></td><td class="vtop">0.77</td><td class="vtop">1.32</td><td class="text_lf vtop">Crandall (1964:312); Poglayen-Neuwall (1987)</td></tr> +<tr><td class="text_lf"> </td><td class="bl vtop"> </td><td class="vtop">1.75</td><td colspan=2> </td><td class="vtop"> 0.65<a href="#Footnote_C_15" class="fnanchor">[c]</a></td><td class="vtop"> </td><td class="vtop">0.84</td><td> </td></tr> +<tr><td class="text_lf vtop"><i>Potos flavus</i></td><td class="bl vtop">2490</td><td class="vtop">1.75</td><td class="vtop">0.50</td><td class="vtop">12</td><td class="vtop">0.30</td><td class="vtop">0.63</td><td class="vtop">0.48</td><td class="text_lf">Ford and Hoffmann (1988); Nowak and Paradiso (1983:984)</td></tr> +<tr><td class="text_lf bb vtop"><i>Bassaricyon gabbii</i></td><td class="bb bl vtop">1600</td><td class="bb vtop">1.75</td><td class="bb vtop">0.50</td><td class="bb vtop">15</td><td class="bb vtop">0.32</td><td class="bb vtop">0.71</td><td class="bb vtop">0.45</td><td class="bb text_lf">Eisenberg (1981:489); Nowak and Paradiso (1983:985)</td></tr> +</table> +<br> + +<div class="footnote"> +<a name="Footnote_A_13" id="Footnote_A_13"></a><a href="#FNanchor_A_13"><span class="label">[a]</span></a> r<sub>maxe</sub> = 4.9·m<sup>0.2622</sup>, where m is body mass in grams.<br> +<br> +<a name="Footnote_B_14" id="Footnote_B_14"></a><a href="#FNanchor_B_14"><span class="label">[b]</span></a> Regression of r<sub>max</sub> on body mass (m). Assume r<sub>max</sub> = 1.02 for <i>Procyon cancrivorus</i>: r<sub>max</sub> = 0.00005·m + 0.623; R = 0.19; R<sup>2</sup> = 0.03; Regression of r<sub>maxr</sub> (<a href="#Table_10">Table 10</a>) on H<sub>br</sub> (<a href="#Table_7">Table 7</a>); assume <i>Nasua nasua</i> has the same r<sub>maxr</sub> as <i>Nasua narica</i>: r<sub>maxr</sub> = 3.35·H<sub>br</sub> - 1.11; R = 0.93; R<sup>2</sup> = 0.86.<br> +<br> +<a name="Footnote_C_15" id="Footnote_C_15"></a><a href="#FNanchor_C_15"><span class="label">[c]</span></a> Estimate based on females reproducing in their first (a = 0.83) or second (a = 1.75) year.<br> +<br> +</div> + + +<a name="Nasua_nasua_1"></a> +<p><i>Nasua nasua.</i>—Unfortunately, there is not enough reproductive +data to allow calculation of r<sub>max</sub> for <i>Nasua nasua</i> (<a href="#Table_10">Table +10</a>), therefore, it is not possible to compare the reproductive +potential of this South American coati with its North American +relative, <i>Nasua narica</i>. Given its low Ḣ<sub>b</sub> and relatively +low-quality diet of fruit and terrestrial invertebrates (<a href="#Table_9">Table 9</a>), +however, r<sub>max</sub> of <i>Nasua nasua</i> may be very similar to that of +<i>Nasua narica</i>.</p> + +<a name="Procyon_cancrivorus_1"></a> +<p><i>Procyon cancrivorus.</i>—The age of first female reproduction +for <i>Procyon cancrivorus</i> has not been reported. However, if one +assumes females can reproduce in their first year, r<sub>max</sub> for +<i>Procyon cancrivorus</i> would be 1.02 (132% of expected; <a href="#Table_10">Table +10</a>). If, on the other hand, first female reproduction is delayed +until the second year, r<sub>max</sub> would be 0.65 (84% of predicted; +<a href="#Table_10">Table 10</a>). <i>Procyon cancrivorus</i> has a low Ḣ<sub>b</sub>, reduced litter +size, and small body mass. Its low Ḣ<sub>b</sub> may limit litter size, but +as with <i>Bassariscus astutus</i>, the quality of its diet (a high +percentage of small vertebrates; <a href="#Table_9">Table 9</a>) and its small body +size may make it possible for females to reproduce in their first +year and thus increase the species' reproductive potential. This +reasoning would argue that <i>Procyon cancrivorus</i> probably +enjoys higher, rather than lower, than expected r<sub>max</sub>.</p> + +<a name="Potos_flavus_1"></a> +<p><i>Potos flavus.</i>—In addition to a low Ḣ<sub>b</sub>, this species possesses +other characteristics that limit its reproductive potential: +low-quality diet, delayed reproduction, and birth of a single +young each year. Because there does not appear to be any other +feature of its life history that can counteract the influence of +these factors, r<sub>max</sub> in <i>Potos flavus</i> has evolved to be only 48% +of expected (0.30; <a href="#Table_10">Table 10</a>). Its close relative, the olingo, +<i>Bassaricyon gabbii</i>, appears to share the same condition (<a href="#Table_10">Table +10</a>).</p> + +<a name="Summary_2"></a> +<p><span class="smcap">Summary.</span>—This brief survey illustrates that, with the +exception of <i>Potos flavus</i>, procyonids tend to have values of +r<sub>max</sub> that are higher than those predicted for them on the basis of +mass (<a href="#Table_10">Table 10</a>). Regression analysis indicates that, within the +family, body mass accounts for only a small amount (3%) of +the variation in r<sub>max</sub>, whereas the positive slope of the +correlation between r<sub>maxr</sub> and H<sub>br</sub> (R = 0.93) suggests that low +metabolism has a limiting effect on r<sub>max</sub> (see <a href="#Footnote_B_14">Table 10, footnote +b</a>). The implication here is that low Ḣ<sub>b</sub> would be associated with +a lower rate of biosynthesis, a slower growth rate, and a longer +generation time. Procyonids with low Ḣ<sub>b</sub> but higher than +expected r<sub>max</sub> must possess other traits that serve to offset the +effects of low metabolism. Our survey indicates that the +following features compensate for low Ḣ<sub>b</sub> and help increase +r<sub>max</sub>: (1) a high-quality diet may make biosynthesis and growth +more efficient, thus optimizing the time element associated +<span class="pagenum"><a name="Page_21" id="Page_21">[Pg 21]</a></span> +with each of these processes; (2) larger litter sizes and +cooperation in care of the young may increase survivorship in +spite of a slower growth rate; and (3) an early age of first +reproduction, a long reproductive life span, and moderate-size +litters (two to four young) may in the long run add as many +individuals to the population as a shortened generation time. +Our survey also suggests that, at the other extreme, factors such +as a low-quality diet, reduced litter size, absence of cooperative +care of the young, delayed age of first reproduction, and +shortened reproductive life span all serve to decrease r<sub>max</sub>. +Thus, it is obvious that diet, litter size, social structure, +reproductive strategy, and reproductive life span can operate +synergistically with Ḣ<sub>b</sub> to magnify its influence on r<sub>max</sub> (as with +<i>Procyon lotor</i> and <i>Potos flavus</i>), or they can function in +opposition to Ḣ<sub>b</sub> to change the direction of its influence on r<sub>max</sub> +(as with <i>Bassariscus astutus</i>, <i>Procyon cancrivorus</i>, <i>Nasua +narica</i>, and perhaps <i>Nasua nasua</i>).</p> + +<a name="Basal_Metabolism_2"></a> +<a name="Procyon_lotor_2"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Basal Metabolism and Climatic Distribution</div> + +<p><i>Procyon lotor.</i>—The evolution of a higher Ḣ<sub>b</sub> (<a href="#Table_7">Tables 7</a>,<a href="#Table_8"> 8</a>) +may have been the physiological cornerstone that enabled +<i>Procyon lotor</i> to break out of the mold being exploited by other +procyonids and to generalize its use of habitats and climates. +Once this basic physiological change was in place, selection for +appropriate alterations in thermal conductance, capacity for +evaporative cooling, diversity of diet, and energy storage would +have provided this species with the suite of adaptations needed +to extend its distribution into other habitats and climates. +Support for this concept follows from the fact that high levels +of Ḣ<sub>b</sub> are associated with (1) cold-hardiness in mammals that +live in cold-temperate and arctic climates (Scholander et al., +1950c; Irving et al., 1955; Irving, 1972:115, 116; Shield, 1972; +Vogel, 1980; Golightly and Ohmart, 1983); (2) the ability to +utilize a wide variety of food resources and to occupy a large +number of different environments and habitats (McNab, +1980a); and (3) a high intrinsic rate of natural increase (McNab, +1980a; Hennemann, 1983; Lillegraven et al., 1987; Nicoll and +Thompson, 1987; Thompson, 1987).</p> + +<a name="Other_Procyonids"></a> +<p><span class="smcap">Other Procyonids.</span>—Other procyonids (<i>Potos flavus</i>, +<i>Procyon cancrivorus</i>, <i>Nasua narica</i>, and <i>Nasua nasua</i>) have +lower than predicted Ḣ<sub>b</sub>'s (<a href="#Table_7">Table 7</a>), a characteristic that is +considered to be an energy-saving adaptation for those that live +in relatively stable tropical and subtropical habitats (Müller and +Kulzer, 1977; Chevillard-Hugot et al., 1980; Müller and Rost, +1983). However, <i>Bassariscus astutus</i> is found in tropical, +subtropical, and temperate climates. This species is found from +tropical Mexico to temperate regions of the western United +States (Kaufmann, 1982, 1987; Nowak and Paradiso, +1983:979). In the northern part of its distribution, <i>Bassariscus +astutus</i> lives in habitats that are unstable (arid regions), that are +low in productivity, and that characteristically have marked +seasonal changes in temperature. Its lower than predicted Ḣ<sub>b</sub> +could be an important water-conserving adaptation at times +when temperatures are high (McNab and Morrison, 1963; +McNab, 1966; MacMillen and Lee, 1970; Noll-Banholzer, +1979) and an important energy-conserving mechanism when +cold weather may limit food availability and hunting time +(Scholander et al., 1950c; Wang et al., 1973). As will be seen +later, <i>Bassariscus astutus</i> is unique among procyonids with +lower than predicted Ḣ<sub>b</sub>'s in that it also has a lower than +predicted C<sub>mw</sub> (<a href="#Table_7">Table 7</a>). This allows it to use less energy than +expected for thermoregulation at low temperatures. Another +species with a similar set of adaptations (lower than predicted +Ḣ<sub>b</sub> and C<sub>mw</sub>) is the arctic hare, <i>Lepus arcticus</i> (Wang et al., +1973), which lives in one of the coldest and least-productive +regions on earth. Wang et al. (1973) suggest that this +combination of adaptations allows <i>Lepus arcticus</i> to better +match its energy requirements to the low productivity of its +environment. A similar relationship may hold for <i>Bassariscus +astutus</i>, particularly in colder arid portions of its distribution, +and may be the reason that it, but not other procyonids with low +Ḣ<sub>b</sub>'s, has been able to inhabit temperate climates.</p> + +<a name="Minimum_Thermal_Conductance_3"></a> +<a name="Background_4"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Minimum Thermal Conductance</div> +<div class="caption4">Background</div> + +<p>Thermal conductance is a measure of the ease with which +heat is passively transferred to or from a body through its +tissues and pelt. Within T<sub>n</sub>, a mammal is able to vary its thermal +conductance over a wide range of values by changing heat +transfer characteristics of both of these layers. Minimum +thermal conductance occurs when total heat transfer through +these layers is reduced to its lowest possible rate. This +minimum value, which is the reciprocal of maximum resistance, +occurs, theoretically, but not always practically (see +McNab, 1988b), at the animal's T<sub>lc</sub> and is best estimated under +standard conditions in a metabolism chamber (McNab, 1980b; +Aschoff, 1981). Minimum thermal conductance scales to body +mass (McNab and Morrison, 1963; Herreid and Kessel, 1967; +McNab, 1970, 1979b; Bradley and Deavers, 1980; Aschoff, +1981). Therefore, to make comparisons between species of +various sizes, we scaled out body mass by expressing C<sub>mw</sub> as +the ratio of measured to predicted values (C<sub>mwr</sub>; <a href="#Table_7">Table 7</a>). These +ratios were used to make comparisons of heat-transfer +characteristics between species that occupy different habitats or +climates.</p> + +<a name="Effect_of_Molt_on_Thermal_Conductance"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Effect of Molt on Thermal Conductance</div> + +<p>In summer, T<sub>lc</sub>'s of male and female <i>Procyon lotor</i> (<a href="#Fig_2">Figure +2</a>) were very similar to those of other procyonids (22°C-26°C; +<a href="#Table_7">Table 7</a>). In winter, T<sub>lc</sub> of both sexes shifted downward to 11°C +(<a href="#Fig_3">Figure 3</a>). This seasonal shift in T<sub>lc</sub> occurred as the result of a +seasonal change in minimum thermal conductance (<a href="#Table_3">Table 3</a>). +For many northern mammals, a seasonal change in thermal +conductance is partly mediated via cyclic changes in the +insulative quality of their pelt (Scholander et al., 1950a; Irving +et al., 1955; Hart, 1956, 1957; Irving, 1972:165).</p> + +<p><span class="pagenum"><a name="Page_22" id="Page_22">[Pg 22]</a></span> +<i>Procyon lotor</i> begins to shed its heavy winter coat about the +time its young are born. Molt progresses through summer and +by late August the new coat is complete (Stuewer, 1942). +During its summer molt, <i>Procyon lotor</i>'s C<sub>mw</sub> increased by +about 49% over the value for female raccoons in winter (<a href="#Table_3">Table +3</a>). In summer, therefore, it had the highest mass specific C<sub>mw</sub> +of those procyonids considered (C<sub>mwr</sub> = 1.77 and 1.79; <a href="#Table_7">Table 7</a>). +An increase in thermal conductance facilitates passive heat loss +for temperate and arctic species, and this serves as an important +thermoregulatory adaptation during warm summer months +(Scholander et al., 1950c; Irving et al., 1955; Hart, 1956, 1957; +Irving, 1972:165). This adaptation is particularly important to +those temperate- and arctic-zone species (including raccoons) +whose Ḣ<sub>b</sub>'s do not decrease during summer (Irving et al., +1955). From August on, the fur of <i>Procyon lotor</i> becomes +increasingly longer and heavier, with peak, or prime, condition +occurring in late fall and early winter (Stuewer, 1942). +Minimum conductance of our captive raccoons was lowest in +winter (C<sub>mwr</sub> = 1.15) when their pelts were in prime condition +(<a href="#Table_3">Tables 3</a>,<a href="#Table_7"> 7</a>). Because "primeness" of raccoon pelts varies +geographically, thicker pelts being associated with colder +climates (Goldman, 1950:21; Whitney and Underwood, +1952:24-41), the degree of seasonal change in C<sub>mw</sub> must also +vary geographically.</p> + +<p>The only other procyonid for which a seasonal molt has been +described is <i>Bassariscus astutus</i>. Molt in this species extends +from late summer to late fall (Toweill and Toweill, 1978). How +molt effects thermal conductance in <i>Bassariscus astutus</i> is not +known because metabolic data for this species (<a href="#Table_7">Table 7</a>) +apparently were collected only when their pelts were in prime +condition (Chevalier, 1985).</p> + +<p>Goldman (1950:20) reports that <i>Procyon cancrivorus</i> does +not have a seasonal molt. Like other tropical procyonids, +<i>Procyon cancrivorus</i> lives in an environment that has the +following characteristics: high even temperatures throughout +the year (1°C-13°C difference in monthly mean temperature), +a greater range in temperature between day and night than in +mean monthly temperature throughout the year, uniform +lengths of day and night, seasonal variation in rainfall, and +lowest temperatures during the rainy season(s) (Kendeigh, +1961:340). In such a stable environment there would be no +advantage to a sharply defined seasonal molt cycle that could +place an animal in thermoregulatory jeopardy by increasing its +thermal conductance. This would be particularly true for +animals like tropical procyonids that have lower than predicted +Ḣ<sub>b</sub>'s but that maintain typical eutherian body temperatures +(<a href="#Table_7">Table 7</a>). Consequently, molt in all tropical procyonids may +either be prolonged or continuous. This is a feature of their +biology that needs to be examined in more detail.</p> + +<a name="Comparison_of_Thermal_Conductances"></a> +<a name="Procyon_lotor_versus_Tropical_Procyonids"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Comparison of Thermal Conductances</div> + +<p><i>Procyon lotor</i> <span class="smcap">versus Tropical Procyonids</span>.—C<sub>mwr</sub> for +<i>Procyon lotor</i> in winter was 1.15, which is similar to the values +for <i>Potos flavus</i> and <i>Procyon cancrivorus</i>, 1.02 and 1.25, +respectively (<a href="#Table_7">Table 7</a>). These two tropical species, therefore, +have C<sub>mw</sub>'s that are similar on a mass specific basis to the value +for <i>Procyon lotor</i> in winter. However, at their T<sub>lc</sub>'s, the thermal +gradient sustained by these tropical animals is only about 11°C, +whereas for <i>Procyon lotor</i> in winter it was 26.5°C. Examination +of <a href="#Eq_4">Eq. 4</a> with respect to these thermal gradients suggests that +tropical procyonids achieve such low C<sub>mw</sub>'s by virtue of their +lower than predicted Ḣ<sub>b</sub>'s rather than by having pelts that are +exceptionally good insulators. In fact, the insulation afforded +by the pelts of these tropical procyonids is about the same as +that of the 50 g arctic lemming, <i>Dicrostonyx groenlandicus +rubricatus</i>, whose coat has an insulative value that is about half +that of the hare, <i>Lepus americanus</i>, red fox, <i>Vulpes fulva +alascensis</i>, and pine martin, <i>Martes americana</i>, animals +comparable in size to these procyonids (Scholander et al., +1950a). Therefore, pelts of these tropical procyonids do not +have the same insulative value as the prime winter coat of +<i>Procyon lotor</i>.</p> + +<p><i>Nasua narica</i> and <i>Nasua nasua</i> have tropical and subtropical +distributions and they are the only procyonids that are diurnal +(Kaufmann, 1962:103-105, 1982, 1987). Because they are +active during the day they experience a more extreme thermal +environment (higher T<sub>a</sub>'s and solar radiation) than their +nocturnal cousins. Values of C<sub>mwr</sub> for <i>Nasua narica</i> (1.45 and +1.55) and <i>Nasua nasua</i> (1.24 and 1.65) are higher than those +for <i>Procyon cancrivorus</i> or <i>Potos flavus</i> (<a href="#Table_7">Table 7</a>). Thus, these +coatis have higher mass specific C<sub>mw</sub>'s than their nocturnal +tropical cousins. A high C<sub>mw</sub> reduces the cost of thermoregulation +in hot environments because it increases an animal's +ability to lose excess heat passively. The higher C<sub>mw</sub>'s of these +coatis serve as an adaptation that contributes to the success of +their diurnal life style as well as their ability to expand their +habitat use to areas with less thermal stability, such as oak and +pine woodlands and deserts.</p> + +<a name="Bassariscus_astutus_2"></a> +<p><i>Bassariscus astutus.</i>—This species has the lowest mass +specific C<sub>mw</sub> of these procyonids (C<sub>mwr</sub> = 0.85; <a href="#Table_5">Table 7</a>), which +indicates that its pelt has a greater insulative value than the +coats of <i>Potos flavus</i>, <i>Procyon cancrivorus</i>, <i>Nasua nasua</i>, or +<i>Nasua narica</i>. This, coupled with a lower than predicted Ḣ<sub>b</sub>, +allows <i>Bassariscus astutus</i> to maintain T<sub>b</sub> with less energy +expenditure than is possible for any other procyonid of +comparable size; and this combination of adaptations provides +<i>Bassariscus astutus</i> with a distinct energy advantage in +environments that have low productivity (Wang et al., 1973). +The evolution of a pelt that provides better insulation must be +considered an, important contributing factor for the spread of +this species into desert regions of the western United States.</p> + +<a name="Thermoregulation_1"></a> +<a name="Background_5"></a> +<a name="Thermoregulation_2"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Thermoregulation and Use of +Stored Fat at Low Temperatures</div> +<div class="caption4">Background</div> + +<p><span class="smcap">Thermoregulation.</span>—At temperatures below a mammal's +T<sub>n</sub>, heat loss exceeds Ḣ<sub>b</sub>. To maintain T<sub>b</sub> under these +<span class="pagenum"><a name="Page_23" id="Page_23">[Pg 23]</a></span> +conditions, metabolic rate must be increased (<a href="#Eq_4">Eq. 4</a>). <i>Procyon +lotor</i> in summer during its annual molt (<a href="#Table_5">Table 5</a>; <a href="#Fig_2">Figure 2</a>), +<i>Bassariscus astutus</i> (Chevalier, 1985), <i>Nasua nasua</i> (Chevillard-Hugot +et al., 1980; Mugaas et al., in prep.), <i>Nasua narica</i> +(Scholander et al., 1950b; Mugaas et al., in prep.), and <i>Potos +flavus</i> (Müller and Kulzer, 1977; Müller and Rost, 1983) all are +able to elevate their metabolic rates by 130% above basal when +they are exposed to T<sub>a</sub> = 0°C. <i>Procyon cancrivorus</i> responds to +0°C with an increase in metabolic rate of 257% above basal +(Scholander et al., 1950b). All animals listed have about the +same T<sub>lc</sub> and T<sub>b</sub>, so the temperature differential producing this +response is about the same for each species. Metabolic ability +to defend body temperature against low ambient temperatures, +therefore, is well developed in these procyonids. Such large +increases in metabolic rate are energetically expensive, and if +these animals were routinely exposed to T<sub>a</sub> = 0°C, it would be +difficult for them to acquire enough food each day to maintain +endothermy. Raccoons in winter pelage, however, need only +elevate their metabolic rate by 47% above basal to maintain +endothermy at T<sub>a</sub> = 0°C (<a href="#Table_5">Table 5</a>; <a href="#Fig_3">Figure 3</a>). Each year at the +completion of its molt, the raccoon's highly insulative pelt is +renewed. This lowers their T<sub>lc</sub> by 9°C to 15°C below that +measured for them in summer (<a href="#Fig_3">Figure 3</a>) and decreases their +cost of thermoregulation at low temperatures. The increased +insulative capacity of their pelt is one of the primary +adaptations that has allowed <i>Procyon lotor</i> to extend its +distribution into cold climates.</p> + +<a name="Stored_Fat"></a> +<p><span class="smcap">Stored Fat.</span>—Cyclic fattening is an integral and important +part of a raccoon's annual cycle (Mugaas and Seidensticker, +ms); however, it has not been reported for other procyonids. +During winter in parts of the United States and Canada, +raccoons are confined to their dens for variable periods of time +(days to months) depending on the severity of the weather +(Stuewer, 1943:223-225; Whitney and Underwood, 1952:108-116; +Sharp and Sharp, 1956; Mech et al., 1968; Schneider +et al., 1971). During this confinement, they do not hibernate but +rather enter a state of "dormancy" and become inactive. While +dormant they remain endothermic (T<sub>b</sub> > 35°C; Thorkelson, +1972:87-90) and derive most of their energy requirement from +fat reserves accumulated during fall. The rate at which fat stores +are consumed during winter dormancy depends on the +thermoregulatory requirement imposed on them by local +weather conditions, the insulative quality of their pelt, and any +advantage they may gain by seeking shelter in a den.</p> + +<a name="Thermal_Model"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Thermal Model of the Raccoon and Its Den</div> + +<p>Heat transfer between an animal and its environment is a +function of the interaction of its body temperature and thermal +conductance with various environmental variables (air temperature, +wind speed, vapor pressure, and thermal radiation). +When a raccoon is outside its den, its thermal conductance +(C<sub>mw</sub>) is the only barrier to heat transfer with the external +environment. However, when it enters a tree den, a raccoon +imposes two other thermal barriers between itself and the +external environment: (1) conductance of the air space between +its fur and the den's walls (C<sub>a</sub>) and (2) conductance of the den's +walls (C<sub>d</sub>; Thorkelson, 1972:59-63; Thorkelson and Maxwell, +1974). Thorkelson and Maxwell (1974) modeled heat transfer +of a simulated raccoon (a water-filled aluminum cylinder +equipped with a heater and covered with a raccoon pelt) in a +closed tree den. In their system, 65% of resistance to heat flux +was attributable to the pelt, whereas the remainder (35%) was +due to C<sub>a</sub> and C<sub>d</sub>. Because resistance is the inverse of +conductance, and resistances for the raccoon and its den are +arranged in series, we can estimate total conductance (C<sub>t</sub>) of +this system with <a href="#Eq_7">Eq. 7</a>.</p> + +<a name="Eq_7"></a> +<table width="100%" summary="Eq. 1"> +<tr><td class="center">1/C<sub>t</sub> = 1/C<sub>mw</sub> + 1/C<sub>a</sub> + 1/C<sub>d</sub></td><td class="text_rt">Eq. 7</td></tr> +</table> + +<p>Minimum thermal conductance C<sub>mw</sub> for raccoons in winter +was 0.0172 mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>·°C<sup>-1</sup> (<a href="#Table_3">Table 3</a>). Based on Thorkelson +and Maxwell's (1974) model we let 1/C<sub>mw</sub> = 0.65(1/C<sub>t</sub>) = 1/0.0172 mL +O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>·°C<sup>-1</sup>, and 1/C<sub>a</sub> + 1/C<sub>d</sub> = 0.35(1/C<sub>t</sub>). Substituting +these values into <a href="#Eq_7">Eq. 7</a> and solving for C<sub>t</sub> yields 0.0112 +mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>·°C<sup>-1</sup>, a value that is 35% lower than that of the +animal alone. Substituting this value and the value for basal +metabolism of winter raccoons (0.47 mL O<sub>2</sub>·g<sup>-1</sup>·h<sup>-1</sup>; <a href="#Table_7">Table 7</a>) +into <a href="#Eq_4">Eq. 4</a> and solving for (T<sub>b</sub> - T<sub>a</sub>) yields a new temperature +differential of 42°C. Therefore, by using tree dens, raccoons in +north central Virginia, with T<sub>b</sub> = 37°C (<a href="#Fig_7">Figure 7</a>), could +effectively reduce their T<sub>lc</sub> from 11°C to -5°C and markedly +reduce their metabolic cost of thermoregulation.</p> + +<a name="Metabolic_Advantage_of_the_Den"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Metabolic Advantage of the Den</div> + +<p>Given prevailing winter temperatures in north central +Virginia (see "Materials and Methods"), adult raccoons in that +area should be able to sustain endothermy most of the time they +are in their dens by simply maintaining Ḣ<sub>b</sub>. Depending on the +mass of their stored fat, they could remain in their dens for +several weeks without eating (Mugaas and Seidensticker, ms). +The thermal advantage of a den could be further enhanced +during colder temperatures if two or more raccoons occupied it +at the same time and huddled together, and/or if these animals +could reduce C<sub>mw</sub> even more by lowering T<sub>b</sub> and cooling their +extremities. Although we do not have any data to verify the +second mechanism, there are many accounts in natural history +literature that document raccoons occupying dens together +(Lotze and Anderson, 1979). This habit could be particularly +important for the young of the year and may be one reason why +they often continue to den with their mothers during winter +(Lotze and Anderson, 1979; Seidensticker et al., 1988). +Raccoons that live in colder climates, such as Minnesota, +undoubtedly obtain the same advantage from a den as Virginia +animals, but because of their greater body mass, longer fur, and +potentially lower C<sub>mw</sub>, T<sub>lc</sub> of a Minnesota raccoon in a den +could be even lower than what we calculated for Virginia +raccoons. Therefore, when they are in their dens, raccoons +living in very cold climates also may be able to maintain +homeothermy with a basal level of metabolism.<span class="pagenum"><a name="Page_24" id="Page_24">[Pg 24]</a></span></p> + +<a name="Thermoregulation_3"></a> +<a name="Background_6"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Thermoregulation at High Temperatures</div> +<div class="caption4">Background</div> + +<p>In hot environments mammals depend on behavior to +minimize their thermal load (escape to shaded or cooler +microclimates, use posture and orientation to wind and sun, +restrict activity, become nocturnal, etc.) and on evaporative +water loss to rid themselves of excess heat. With regard to +evaporative heat loss, Calder and King (1974:326) arbitrarily +subdivided the response to various T<sub>a</sub>'s as follows: "(1) cool +temperatures at which water loss should be minimized, both to +reduce heat loss and as an adaptation to terrestriality; (2) an +intermediate temperature range wherein evaporation is gradually +increased as dry heat losses are proportionately reduced +with smaller thermal gradients; and (3) warm to hot temperatures +at which evaporation must be actively increased to +dispose of metabolic and exogenous heat loads." Some +mammals are able to thermoregulate very well at high ambient +temperatures via panting or sweating, whereas others have a +very limited capacity. Hence, there is no general approach to +calculating evaporative water loss under these conditions +(Campbell, 1977:85). However, the ratio of evaporative heat +lost to metabolic heat produced can be used to quantify a +species' capacity for evaporative cooling and to make +comparisons between species.</p> + +<a name="Comparison_of_Procyonid_Responses"></a> +<a name="Potos_flavus_2"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Comparison of Procyonid Responses to Heat Stress</div> + +<p><i>Potos flavus.</i>—This species lives in Neotropical forests of +Central and South America. It is nocturnal, arboreal in habit, +and appears to be the most heat-sensitive of these procyonids. +Its T<sub>uc</sub> is at 30°C to 33°C (<a href="#Table_7">Table 7</a>; Müller and Kulzer, 1977; +Müller and Rost, 1983). It begins to pant at about 30°C, but its +efforts at evaporative cooling are very ineffective. At 33°C +<i>Potos flavus</i> can dissipate 33% of its metabolic heat via +evaporative water loss, but at 35°C the efficiency of this +mechanism falls to 20% (Müller and Rost, 1983). Consequently, +when exposed to T<sub>a</sub>'s above 33°C, any kind of +excitement causes its T<sub>b</sub> to rise rapidly in an uncontrolled +manner (Müller and Kulzer, 1977; Müller and Rost, 1983). +These animals rely on their nocturnal and arboreal habits to +keep them out of situations that could lead to hyperthermia +(Müller and Kulzer, 1977; Müller and Rost, 1983).</p> + +<a name="Nasua_nasua_2"></a> +<p><i>Nasua nasua</i> and <i>Nasua narica</i>.—<i>Nasua nasua</i> is abundant +in tropical and subtropical South America, whereas <i>Nasua +narica</i> occupies the same climates in North America from +southern Arizona and New Mexico south through Panama and +on into Colombia and Ecuador (Hall and Kelson, 1959:892; +Ewer, 1973:391, 392; Poglayen-Neuwall, 1975). Both coatis +are diurnal and forage primarily on the ground (Kaufmann, +1962:185-188, 1987; Poglayen-Neuwall, 1975; Nowak and +Paradiso, 1983:982), consequently they are exposed to a more +severe thermal environment while active (higher T<sub>a</sub>'s and solar +radiation) than are nocturnal procyonids. Both coatis are more +heat-tolerant than <i>Potos flavus</i>; their T<sub>uc</sub>'s are higher (33°C-35°C; +<a href="#Table_7">Table 7</a>), they can tolerate T<sub>a</sub>'s of 35°C without raising +their T<sub>b</sub>'s (Chevillard-Hugot et al., 1980; Mugaas et al., in +prep.), and they have a greater capacity for evaporative cooling +than <i>Potos flavus</i> (Mugaas et al., in prep.). The greater heat +tolerance of these coatis is compatible with their diurnal habits +and widespread distribution in a variety of forest habitats in +both tropical and subtropical areas of the western hemisphere.</p> + +<a name="Bassariscus_astutus_3"></a> +<p><i>Bassariscus astutus.</i>—In addition to living in Neotropical +forests of Mexico, <i>Bassariscus astutus</i> also flourishes in hot +arid climates, and it has extended its range much farther north +than <i>Nasua narica</i> (Hall and Kelson, 1959:881,892; Poglayen-Neuwall, +1975; Kaufmann, 1982). Its T<sub>uc</sub> is higher (35.5°C; +<a href="#Table_7">Table 7</a>) than that of <i>Potos flavus</i>, but it is comparable to those +of <i>Nasua nasua</i> and <i>Nasua narica</i>. Its capacity for evaporative +cooling is well developed; at 40°C <i>Bassariscus astutus</i> is able +to dissipate 100% of its resting metabolic heat via evaporative +water loss, and at 45°C it is able to dissipate 172% (Chevalier, +1985). In spite of its great capacity for evaporative cooling, this +species is nocturnal, a habit that, along with its low Ḣ<sub>b</sub>, should +allow it to keep thermoregulatory water requirements to a minimum.</p> + +<a name="Procyon_lotor_3"></a> +<p><i>Procyon lotor.</i>—Our data suggested that T<sub>uc</sub> for <i>Procyon +lotor</i> in winter was comparable to that for <i>Bassariscus astutus</i> +(35°C), and that in summer it was even higher. When exposed +to temperatures near the upper end of its T<sub>n</sub>, <i>Procyon lotor</i> +increased the gradient for passive heat loss with a controlled +rise in T<sub>b</sub> (<a href="#Fig_6">Figure 6</a>). In summer its capacity for passive heat +loss was enhanced by the molt of its heavy winter fur. <i>Procyon +lotor</i>'s capacity for evaporative cooling also appeared to be +well developed, although our animals were not heated to the +point that evaporative cooling was fully expressed (<a href="#Fig_4">Figures 4</a>, +<a href="#Fig_5"> 5</a>). However, <i>Procyon lotor</i> is nocturnal, and this may allow it +to eliminate, or at least reduce, the need for evaporative +cooling, even in hot climates. Thus, <i>Procyon lotor</i> appears to be +well equipped physiologically and behaviorally to cope with +thermal demands of hot environments in its distribution.</p> + +<a name="Procyon_cancrivorus_2"></a> +<p><i>Procyon cancrivorus.</i>—Unfortunately, data for the crab-eating +raccoon are not complete enough at high temperatures to +include it in this survey.</p> + +<a name="Summary_3"></a> +<p><span class="smcap">Summary.</span>—This comparison demonstrates that capacity +for evaporative cooling, tolerance of an elevated T<sub>b</sub> to enhance +passive heat loss, and behavioral avoidance of thermal stress +are the primary methods used by procyonids to thermoregulate +at high temperatures. <i>Procyon lotor</i> and <i>Bassariscus astutus</i>, +whose distributions extend into temperate regions, have +developed these abilities to a greater extent than other +procyonids. <i>Potos flavus</i>, whose distribution is confined to +lowland tropical forests, has the least ability in this regard. +<i>Nasua nasua</i> and <i>Nasua narica</i> appear to have thermoregulatory +abilities that are intermediate to those of <i>Bassariscus +astutus</i> and <i>Potos flavus</i>. This suggests that ancestral procyonids +<span class="pagenum"><a name="Page_25" id="Page_25">[Pg 25]</a></span> +may have had poor to modest ability to thermoregulate +at high temperatures, a condition that would have limited their +ability to leave the thermal stability afforded by tropical forests. +Dispersal into temperate climates, therefore, required not only +increased cold tolerance but also selective enhancement of +those mechanisms used in thermoregulation at high temperatures.</p> + +<a name="Table_11"></a> +<div class="tab_cap"><span class="smcap">Table 11.</span>—Distribution by climate of selected procyonid species.</div> +<br> +<table width="100%" class="center" summary="Distribution by Climate"> +<tr><th class="bt bb">Species</th><th class="bt bl bb">Tropics</th><th class="bt bb">Subtropics</th><th class="bt bb">Mild<a name="FNanchor_A_16" id="FNanchor_A_16"></a><a href="#Footnote_A_16" class="fnanchor">[a]</a><br>temperate</th><th class="bt bb">Cold<a name="FNanchor_B_17" id="FNanchor_B_17"></a><a href="#Footnote_B_17" class="fnanchor">[b]</a><br>temperate</th></tr> +<tr><td class="text_lf"><i>Procyon lotor</i></td><td class="bl">+</td><td>+</td><td>+</td><td>+</td></tr> +<tr><td class="text_lf"><i>Bassariscus astutus</i></td><td class="bl">+</td><td>+</td><td>+</td><td> </td></tr> +<tr><td class="text_lf"><i>Nasua nasua</i></td><td class="bl">+</td><td>+</td><td><td colspan=2> </td></tr> +<tr><td class="text_lf"><i>Nasua narica</i></td><td class="bl">+</td><td>+</td><td colspan=3> </td></tr> +<tr><td class="text_lf"><i>Procyon cancrivorus</i></td><td class="bl">+</td><td>+</td><td colspan=4> </td></tr> +<tr><td class="text_lf bb"><i>Potos flavus</i></td><td class="bl bb">+</td><td class="bb" colspan=5> </td></tr> +</table> +<br> + +<div class="footnote"> +<a name="Footnote_A_16" id="Footnote_A_16"></a><a href="#FNanchor_A_16"><span class="label">[a]</span></a> Extends from the subtropics north to the northern limit of <i>Bassariscus astutus</i>' distribution (Hall and Kelson, 1959:881), which approximates the 10°C isotherm for average annual temperature in the United States (Kincer, 1941).<br> +<br> +<a name="Footnote_B_17" id="Footnote_B_17"></a><a href="#FNanchor_B_17"><span class="label">[b]</span></a> Extends northward from the 10°C isotherm for average annual temperature in the United States.<br> +<br> +</div> + +<a name="Composite_Scores"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Composite Scores of Adaptive Units and Geographic Distribution</div> + +<p>In <a href="#Table_11">Table 11</a>, procyonid species are arranged in descending +order with respect to the number of major climates that are +included in their geographic distributions (Hall and Kelson, +1959:878-897; Poglayen-Neuwall, 1975; Kortlucke and Ramirez-Pulido, +1982; Nowak and Paradiso, 1983:977-985). +Composite scores ranged from a high of 1.47 for <i>Procyon lotor</i> +to a low of 0.39 for <i>Potos flavus</i>, whereas <i>Nasua nasua</i>, <i>Nasua +narica</i>, <i>Procyon cancrivorus</i>, and <i>Bassariscus astutus</i> had +intermediate values ranging from 0.64 to 0.79 (<a href="#Table_12">Table 12</a>). +<a href="#Fig_8">Figure 8</a> demonstrates that there is a direct relationship between +the number of climates these species occupy and their +composite scores. Regression analysis (Y = 2.68·X + 0.24; +where Y is number of climates, and X is composite score) +demonstrates a high degree of correlation between these +variables (R = 0.94) and indicates that 89% of the variance in +distribution can be explained by composite scores. The various +combinations of adaptations expressed by these species do, +therefore, play a role in delimiting their climatic (latitudinal) +distributions.</p> + +<p><i>Procyon lotor's</i> normalized scores were higher in all +categories than those of other procyonids. <i>Procyon lotor</i>, +therefore, possesses those traits that have allowed it to become +the premier climate generalist of the procyonid family. As an +adaptive unit, these traits provide <i>Procyon lotor</i> with the +physiological and behavioral flexibility required to take full +advantage of a wide range of climates and habitats, and its +distribution verifies that it has done so. Even so, it is probably +not fair to assume that this species represents a perfect +physiological match with climate over its entire distribution. +<i>Procyon lotor</i> is, in many respects, still a forest-dwelling +species, and its ability to expand its distribution into other +habitats such as prairie and desert may well be due, in part, to +its use of behavior to take advantage of favorable microclimates +in otherwise hostile environments (Bartholomew, 1958, +1987). This feature of <i>Procyon lotor's</i> biology needs to be +further examined.</p> + +<a name="Table_12"></a> +<div class="tab_cap"><span class="smcap">Table 12.</span>—Normalized and composite scores for selected procyonids. (H<sub>br</sub> = +ratio of measured to predicted basal metabolism (<a href="#Table_7">Table 7</a>), C<sub>mwr</sub> = ratio of +measured to predicted minimum thermal conductance (<a href="#Table_7">Table 7</a>), D<sub>dr</sub> = ratio of +food categories actually utilized by each species to total food categories eaten +by all six species (calculated from <a href="#Table_9">Table 9</a>), r<sub>maxr</sub> = ratio of calculated to +expected r<sub>max</sub> (<a href="#Table_10">Table 10</a>).)</div> +<br> +<table width="100%" class="center" summary="Normalized and composite scores for selected procyonids"> +<tr><th class="bt bb" rowspan=2>Species</th><th class="bt bl bb" colspan=3>Normalized scores</th><th class="bt bb" rowspan=2>Composite<a name="FNanchor_A_18" id="FNanchor_A_18"></a><a href="#Footnote_A_18" class="fnanchor">[a]</a><br>score</th></tr> +<tr><th class="bl bb">H<sub>br</sub>/C<sub>mwr</sub></th><th class="bb">D<sub>dr</sub></th><th class="bb">r<sub>maxr</sub></th></tr> +<tr><td class="text_lf"><i>Procyon lotor</i></td><td class="bl">0.95</td><td>0.95</td><td>2.52</td><td>1.47<td></tr> +<tr><td class="text_lf"><i>Bassariscus astutus</i></td><td class="bl">0.80</td><td>0.33</td><td>1.24</td><td>0.79<td></tr> +<tr><td class="text_lf"><i>Nasua nasua</i></td><td class="bl">0.48</td><td>0.33</td><td> 1.11<a name="FNanchor_B_19" id="FNanchor_B_19"></a><a href="#Footnote_B_19" class="fnanchor">[b]</a></td><td>0.64<td></tr> +<tr><td class="text_lf"><i>Nasua nasua</i></td><td class="bl">0.48</td><td>0.33</td><td> 1.11<a href="#Footnote_B_19" class="fnanchor">[b]</a></td><td>0.64<td></tr> +<tr><td class="text_lf"><i>Nasua narica</i></td><td class="bl">0.40</td><td>0.53</td><td>1.11</td><td>0.68<td></tr> +<tr><td class="text_lf"><i>Procyon cancrivorus</i></td><td class="bl">0.55</td><td>0.33</td><td>1.32</td><td>0.73<td></tr> +<tr><td class="text_lf bb"><i>Potos flavus</i></td><td class="bl bb">0.60</td><td class="bb">0.11</td><td class="bb">0.48</td><td class="bb">0.39<td></tr> +</table> +<br> +<div class="footnote"> +<a name="Footnote_A_18" id="Footnote_A_18"></a><a href="#FNanchor_A_18"><span class="label">[a]</span></a> Composite score = [(H<sub>br</sub>/C<sub>mwr</sub>) + D<sub>dr</sub> + r<sub>maxr</sub>]/3.<br> +<br> + +<a name="Footnote_B_19" id="Footnote_B_19"></a><a href="#FNanchor_B_19"><span class="label">[b]</span></a> Value calculated for <i>Nasua narica</i> (<a href="#Table_10">Table 10</a>) and used with the assumption that it must be similar to the value for <i>Nasua nasua</i>.<br> +<br> +</div> + +<p>All five species with low Ḣ<sub>b</sub>'s have composite scores less +than 1.0 (<a href="#Table_12">Table 12</a>; <a href="#Fig_8">Figure 8</a>). Four of these five, <i>Nasua nasua</i>, +<i>Nasua narica</i>, <i>Procyon cancrivorus</i>, and <i>Potos flavus</i>, have +H<sub>br</sub>/C<sub>mwr</sub> ratios that are 0.6 or less, which indicates +they are the least cold-tolerant procyonids (McNab, 1966). +These four species also are confined to either tropic, or tropic +and subtropic climates (<a href="#Table_11">Table 11</a>). This suggests that these +species share a common thermoregulatory adaptation that +represents a specialization to these climates. Attendant with +this adaptation, however, is a high cost of thermoregulation at +<span class="pagenum"><a name="Page_26" id="Page_26">[Pg 26]</a></span> +temperatures below their T<sub>lc</sub>, and this must be an important +factor in limiting their distributions to tropic and subtropic +climates. Differences in their distributions within these +climates, therefore, must hinge more on differences in their D<sub>dr</sub> +and r<sub>maxr</sub> values than on differences in their H<sub>br</sub>/C<sub>mwr</sub> ratios. +This is supported by the fact that <i>Potos flavus</i>, which has the +lowest D<sub>dr</sub> and r<sub>maxr</sub> values, is confined to a single climate, +whereas <i>Nasua nasua</i>, <i>Nasua narica</i>, and <i>Procyon cancrivorus</i> +each possess larger D<sub>dr</sub> and r<sub>maxr</sub> values and are found +in two climates. Thus, <i>Potos flavus</i>, with its highly specialized +diet and low reproductive potential, is the most ecologically +specialized of these procyonids, and its distribution is limited to +the single climate that can provide its requirements. <i>Nasua +nasua</i>, <i>Nasua narica</i>, and <i>Procyon cancrivorus</i> are less +specialized and thus show more ecological flexibility in their +distributions.</p> + +<a name="Fig_8"></a> +<div class="center"> + <img src="images/fig_8.png" width="369" height="339" title="Relationship between number of climates in which a species is found and its composite score." alt="number of climates vs composite score"><br><br> + <div class="fig_cap"><span class="smcap">Figure 8.</span>—Relationship between number of climates in which a species is found and its composite score. Symbols for <i>Nasua nasua</i> overlap at coordinates (0.64, 2). Solid line represents linear regression of climates (Y) on composite scores (X): Y = 2.68·X + 0.24; R = 0.94.</div> +</div> + +<p><i>Bassariscus astutus</i>, the other species with low Ḣ<sub>b</sub>, is found +in three climates, which indicates that it has greater ecological +flexibility than <i>Nasua nasua</i>, <i>Nasua narica</i>, or <i>Procyon +cancrivorus</i>. D<sub>dr</sub> and r<sub>maxr</sub> are comparable for these four species +(<a href="#Table_12">Table 12</a>). This suggests that the greater ecological flexibility +of <i>Bassariscus astutus</i> is derived largely from its greater cold +tolerance. <i>Bassariscus astutus</i> has a more insulative pelt than +these other procyonids (C<sub>mwr</sub> = 0.85; <a href="#Table_7">Table 7</a>), so its H<sub>br</sub>/C<sub>mwr</sub> +ratio is higher (0.80; <a href="#Table_12">Table 12</a>). This, and its greater capacity for +evaporative cooling (Chevalier, 1985), allows <i>Bassariscus +astutus</i> to take advantage of a wider range of thermal +environments than these other species. However, even with its +higher H<sub>br</sub>/C<sub>mwr</sub> ratio, the composite score for <i>Bassariscus +astutus</i> is not much different than those for <i>Nasua nasua</i>, +<i>Nasua narica</i>, and <i>Procyon cancrivorus</i> (<a href="#Table_12">Table 12</a>). Consequently, +<i>Bassariscus astutus</i> is found in more climates than +would be predicted for it on the basis of its composite score +(<a href="#Fig_8">Figure 8</a>). This suggests that either the H<sub>br</sub>/C<sub>mwr</sub> ratio carries +greater weight in determining distribution than is reflected in +this analysis, or as has been described for some other species +(Bartholomew, 1958, 1987), <i>Bassariscus astutus</i> may extend +its distribution farther than expected via use of its behavior. In +either case, for procyonids with low Ḣ<sub>b</sub>, <i>Bassariscus astutus</i> +represents the pinnacle of adaptation for climate generalization.</p> + +<a name="Evolution_of_Metabolic_Adaptations"></a> +<a name="Evolution_of_Low_Basal_Metabolic_Rate"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Evolution of Metabolic Adaptations</div> +<div class="caption4">Evolution of Low Basal Metabolic Rate</div> + +<p>A radiation of frugivorous and omnivorous Procyoninae +(<a href="#Table_1">Table 1</a>) occurred in the middle and late Miocene of North +America. It included origins of such terrestrial genera as +<i>Cyonasua</i>, <i>Nasua</i>, and <i>Procyon</i> (Webb, 1985b). The earliest +procyonid genus to find its way to South America was +<i>Cyonasua</i>, an omnivorous carnivore that presumably split, +along with its sister genus <i>Arctonasua</i>, from a common North +American ancestor (Baskin, 1982; Webb, 1985b). <i>Cyonasua</i>, +about the size of present-day raccoons, was adapted to a wide +range of habitats and was probably comparable to modern +raccoons with respect to the breadth of its feeding habits +(Webb, 1985b; Marshall, 1988). Because North American +<i>Arctonasua</i> was about the same size as <i>Cyonasua</i> (Webb, +1985b) and shared a number of characters with it (Baskin, +1982), we speculate that it also may have had similar habits and +occupied similar climates and habitats. <i>Bassariscus</i>, another +member of Procyoninae, had an even earlier origin in tropical +North America (Webb, 1985b). The origin of the small arboreal +forms <i>Potos</i> and <i>Bassaricyon</i> (subfamily Potosinae) is obscure +but is thought to have occurred in the rainforests of Central +America (Webb, 1985b). What were the metabolic capabilities +of these early procyonids? We do not know, but for several +million years, from middle to late Miocene, procyonids lived in +tropical and subtropical forests of Central and North America +(Webb, 1985b; Marshall, 1988). Then, in the Pleistocene, +several modern forms crossed the Panamanian land bridge into +similar habitats and climates in South America; but none of +them appear to have spread far enough northward to have +crossed the Bering land bridge.</p> + +<p>Several million years exposure to a tropical environment, +with its continuous high temperatures and modest range of +thermal extremes, would have favored selection of metabolic +and thermoregulatory traits that would minimize energy +requirements: a lower than predicted basal metabolic rate, a +prolonged or continuous molt resulting in very little annual +change in minimum thermal conductance, and a modest +capacity for evaporative cooling. In addition, we would expect +selection to have favored a diverse diet, good reproductive +<span class="pagenum"><a name="Page_27" id="Page_27">[Pg 27]</a></span> +potential, and behavioral flexibility to utilize a variety of +habitats within these climates. Our analysis has shown that +such characteristics are the norm for extant members of this +family living in tropical and subtropical climates, and we +speculate that these traits also were common to early +procyonids and served to restrict them to these climates. Our +speculation is supported by the fact that their known fossil +history from the Miocene is confined to geographic areas that +had tropical and subtropical climates.</p> + +<p>Later on, during Pleistocene glaciations, tropical and +subtropical forests shrank, savannas expanded, and temperate +climate was pushed toward equatorial regions. The opposite +occurred during interglacial periods (Raven and Axelrod, 1975; +Webb, 1977, 1978; Marshall, 1988). Consequently, mid-latitudes +experienced alternating periods of temperate and +tropical, or at least subtropical, climate change. Selection of +characteristics that would have adapted a species with low Ḣ<sub>b</sub> +to temperate as well as tropic or subtropic climates could have +occurred in mid-latitudes at the temperate edge of these tropical +advances and retreats. Our analysis indicates that, for this +purpose, selection would have favored lower than predicted +thermal conductance, seasonal molt, increased capacity for +evaporative cooling, increased tolerance of elevated T<sub>b</sub>, +increased flexibility of thermoregulatory behavior, food habits +that provided for year-round access to a high-quality diet in all +three climates, and a higher than predicted r<sub>max</sub>.</p> + +<p><i>Bassariscus astutus</i> is the only species with low Ḣ<sub>b</sub> that has +all these characteristics, and it is the only one of them that has +added temperate climate to its distribution (<a href="#Table_11">Table 11</a>). This +suggests that <i>Bassariscus astutus</i> is a species that evolved away +from the norm for procyonids with low Ḣ<sub>b</sub>, toward characteristics +that allowed it to become more of a climate generalist. +<i>Potos flavus</i>, with its dietary specialization, low tolerance to +high temperatures, and arboreal mode of existence, has become +a highly specialized species totally dependent on tropical +forests for its survival. As such, it also represents a species that +has evolved away from the procyonid norm and portrays the +extreme in climate specialization. Olingos, <i>Bassaricyon gabbii</i> +(<a href="#Table_1">Table 1</a>), may be similar to <i>Potos flavus</i> in this respect (see +also <a href="#Table_10">Table 10</a>). This suggests that of the extant procyonids, +<i>Nasua nasua</i>, <i>Nasua narica</i>, and <i>Procyon cancrivorus</i> have +retained metabolic and behavioral characteristics that are +closest to those of their Miocene ancestors.</p> + +<a name="Evolution_of_High_Basal_Metabolic_Rate"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption4">Evolution of High Basal Metabolic Rate</div> + +<p>Between the time that <i>Cyonasua</i> appeared and the Panamanian +land bridge was established in the upper Pliocene (4 to 5 +million years ago), northern climates continued their gradual +cooling. This, along with ongoing elevation of the continents +and continuous modification of their mountain ranges, served +to shrink the tropical forest and create pockets of climatic +instability within it and on its edges (Darlington, 1963:578-596; +Marshall, 1988). In areas of instability, selection would +have favored traits that provided for a broader range of thermal +tolerance: higher Ḣ<sub>b</sub>, improved insulative quality of pelt, a +more sharply defined molt cycle, improved capacity for +evaporative cooling, greater D<sub>d</sub>, and higher r<sub>max</sub>. Consequently, +by the upper Pliocene, two metabolically distinct groups of +procyonids could have been established: those species with low +Ḣ<sub>b</sub> living in climatically stable forests and those with higher Ḣ<sub>b</sub> +living in unstable tropical, subtropical, and perhaps temperate +climates.</p> + +<p><i>Procyon lotor</i> is the only extant procyonid with high Ḣ<sub>b</sub>. +<i>Procyon cancrivorus</i> is its congeneric counterpart in Central +and South America (<a href="#Table_1">Table 1</a>), and the two species are sympatric +in Panama and Costa Rica. However, in terms of its +metabolism, thermal conductance, molt, diversity of diet, r<sub>max</sub>, +and climatic distribution, <i>Procyon cancrivorus</i> shares more in +common with other procyonids than it does with <i>Procyon lotor</i> +(<a href="#Table_7">Tables 7</a>,<a href="#Table_11"> 11</a>,<a href="#Table_12"> 12</a>; <a href="#Fig_8">Figure 8</a>). This suggests that metabolically +<i>Procyon lotor</i> portrays a divergent line of this genus that arose +as the result of a series of mutations that gave rise to different +metabolic characteristics. This view is in keeping with a recent +phylogenetic analysis of this family that shows the genus +<i>Procyon</i> to be highly derived (Decker and Wozencraft, 1991). +Consequently, it would be instructive and would add to our +knowledge of the evolution of climatic adaptation to know +more about the genetic relatedness of these two species as well +as their historical relationship.</p> + +<p>Genus <i>Procyon</i> appears in the fossil record (Hemphillian and +Blancan ages; Baskin, 1982) prior to Pleistocene glaciations. +During the Pleistocene, there were four different glacial +advances and retreats in a relatively short time period (the first +appearing little more than a million years ago; Darlington, +1963:578-596; Webb, 1985a; Marshall, 1988). Glacial retreats +created pulses of time during which subtropic and temperate +climates advanced toward the poles into areas with large +seasonal differences in light/dark cycles, whereas glacial +advances pushed these climates southward into areas having +smaller seasonal differences in light/dark cycles (Raven and +Axelrod, 1975; Webb, 1977, 1978; Marshall, 1988). Those +members of the genus <i>Procyon</i> caught in these wide latitudinal +fluctuations would have experienced conditions favorable to +continued selection for characteristics conducive to physiologic +adaptation to a wide range of climatic conditions. <i>Procyon +lotor</i> is the only member of its genus to have survived this +selective process, and as we have seen, it does possess traits +that adapt it to a wide range of climatic conditions. Primary +among these is its higher Ḣ<sub>b</sub>, which provides it with advantages +not shared with other procyonids (see earlier discussion). Three +other adaptations also have had a profound influence on +<i>Procyon lotor</i>'s ability to generalize its use of climate: (1) the +increased insulative quality of its pelt coupled with its sharply +defined molt cycle, which allows for a large annual change in +thermal conductance; (2) its annual cycle of fat storage; and (3) +a diverse high-quality diet. The first two of these adaptations +<span class="pagenum"><a name="Page_28" id="Page_28">[Pg 28]</a></span> +required evolution of neuroendocrine pathways capable of +responding to time-dependent environmental cues such as +changing day length, changing temperature, etc. Such conditions +would have been available as selective stimuli in +high-latitude forests and savannas of interglacial periods. +<i>Procyon lotor</i>'s elevated basal metabolic rate would have +increased its overall energy requirement, and it makes good +intuitive sense, therefore, that evolution during the Pleistocene +also would have favored selection of a diverse diet containing +many items of high nutritive value.</p> + +<a name="Summary_4"></a> +<span class="pagenum"><a href="#toc">[↑ TOC]</a></span> +<div class="caption3">Summary</div> + +<p>Our analysis has illustrated that within Procyonidae there are +two distinct modes of metabolic adaptation to climate. One is +typified by those species with low Ḣ<sub>b</sub>'s (<i>Bassariscus astutus</i>, +<i>Nasua nasua</i>, <i>Nasua narica</i>, <i>Procyon cancrivorus</i>, and <i>Potos +flavus</i>), and the other by <i>Procyon lotor</i> with its higher Ḣ<sub>b</sub>. +Those with low Ḣ<sub>b</sub>'s have more restricted geographic distributions, +and, with the exception of <i>Bassariscus astutus</i>, they are +all confined to tropical and subtropical areas. The fossil history +of this family indicates that it had its origins in tropical forests +of North and Central America. This indicates that those +procyonids whose distributions are still primarily restricted to +tropical forests share many of the metabolic adaptations +characteristic of their ancestors. We speculate, therefore, that +ancestral procyonids had a lower than predicted Ḣ<sub>b</sub>, a pelt with +modest to poor insulative quality, good thermogenic ability but +poor heat tolerance, modest to poor capacity for evaporative +cooling, no well-defined molt cycle, no cyclic period of +fattening, nocturnal habits, and a modestly diverse diet of +high-enough quality to provide for an average reproductive +potential. Although this pedigree contributed to the success of +this family in tropical and subtropical forests, it limited the +ability of its members to expand their distributions into cooler, +less stable climates. Viewed in this perspective, <i>Procyon +lotor</i>'s high basal metabolic rate, extraordinarily diverse diet, +well-defined cyclic changes in fat content and thermal +conductance, high level of heat tolerance, high capacity for +evaporative cooling, and high reproductive potential all stand +out in sharp contrast to the condition described for other +procyonids. This suggests that the North American raccoon +represents culmination of a divergent evolutionary event that +has given this species the ability to break out of the old +procyonid mold and carry the family into new habitats and +climates.</p> + + +<br> +<a name="Appendix_List_of_Symbols"></a> +<p><span class="pagenum"><a href="#toc">[↑ TOC]</a></span></p> +<br> +<p><span class="pagenum"><a name="Page_29" id="Page_29">[Pg 29]</a></span></p> +<div class="caption2">Appendix: List of Symbols</div> + +<table width="100%" summary="List of Symbols" cellpadding=7> +<tr><td>a</td><td>potential age of females first producing young</td></tr> +<tr><td>b</td><td>potential annual birth rate of female young</td></tr> +<tr><td>C<sub>a</sub></td><td>conductance of air</td></tr> +<tr><td>C<sub>d</sub></td><td>conductance of den walls</td></tr> +<tr><td>C<sub>m</sub></td><td>minimum thermal conductance</td></tr> +<tr><td>C<sub>md</sub></td><td>minimum dry thermal conductance</td></tr> +<tr><td>C<sub>mw</sub></td><td> minimum wet thermal conductance</td></tr> +<tr><td>C<sub>mwr</sub></td><td>ratio of measured to predicted minimum wet thermal conductance</td></tr> +<tr><td>C<sub>t</sub></td><td>total conductance</td></tr> +<tr><td>D<sub>d</sub></td><td> diversity of diet</td></tr> +<tr><td>D<sub>dr</sub></td><td> ratio of food categories actually used by a species to the total number of food categories taken by all species tested</td></tr> +<tr><td>Ė</td><td>evaporative water loss</td></tr> +<tr><td>E<sub>c</sub></td><td>ratio of evaporative heat lost to metabolic heat produced</td></tr> +<tr><td>Ė<sub>eq</sub></td><td>oxygen equivalent for heat lost by evaporation</td></tr> +<tr><td>Ḣ<sub>b</sub></td><td> basal metabolic rate</td></tr> +<tr><td>Ḣ<sub>r</sub></td><td> lowest resting metabolic rate at each temperature</td></tr> +<tr><td>H<sub>br</sub></td><td> ratio of measured to predicted basal metabolic rate</td></tr> +<tr><td>m</td><td>mass of animal</td></tr> +<tr><td>m<sub>w</sub></td><td> mass of water</td></tr> +<tr><td>n</td><td>potential age of females producing their final young</td></tr> +<tr><td>r<sub>max</sub></td><td> intrinsic rate of natural increase</td></tr> +<tr><td>r<sub>maxe</sub></td><td> expected intrinsic rate of natural increase</td></tr> +<tr><td>r<sub>maxr</sub></td><td> ratio of calculated to expected intrinsic rate of natural increase</td></tr> +<tr><td>RQ</td><td> respiratory quotient</td></tr> +<tr><td>T<sub>a</sub></td><td>chamber air temperature</td></tr> +<tr><td>T<sub>b</sub></td><td> body temperature</td></tr> +<tr><td>T<sub>lc</sub></td><td> lower critical temperature</td></tr> +<tr><td>T<sub>n</sub></td><td> thermoneutral zone</td></tr> +<tr><td>T<sub>uc</sub></td><td> upper critical temperature</td></tr> +<tr><td>t</td><td>time</td></tr> +<tr><td><span class="dot">.</span><span class="V">V</span><sub>a</sub></td><td>rate of air flow through <img src="images/u_tube.png" width="14" height="14" border="0" alt="U-tube" title="U-tube">-tubes</td></tr> +<tr><td><span class="dot">.</span><span class="V">V</span><sub>e</sub></td><td>rate of air flow into metabolism chamber</td></tr> +<tr><td>α</td><td>active phase of the daily cycle</td></tr> +<tr><td>γ</td><td>heat equivalent of oxygen</td></tr> +<tr><td>λ</td><td>heat of vaporization of water</td></tr> +<tr><td>ρ</td><td>rest phase of the daily cycle</td></tr> +</table> +<br> + +<p><span class="pagenum"><a name="Page_30" id="Page_30">[Pg 30]</a></span></p> +<br> +<a name="Literature_Cited"></a> +<p><span class="pagenum"><a href="#toc">[↑ TOC]</a></span></p> +<div class="caption2">Literature Cited</div> + +Aschoff, Jürgen<br> + +<div class="reference">1981. 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In his formal plan for the institution, Joseph Henry outlined a +program that included the following statement: "It is proposed to publish a series of reports, +giving an account of the new discoveries in science, and of the changes made from year to year +in all branches of knowledge." This theme of basic research has been adhered to through the +years by thousands of titles issued in series publications under the Smithsonian imprint, +commencing with <i>Smithsonian Contributions to Knowledge</i> in 1848 and continuing with the +following active series:</p> + +<div class="center"> +<i>Smithsonian Contributions to Anthropology</i><br> +<i>Smithsonian Contributions to Botany</i><br> +<i>Smithsonian Contributions to the Earth Sciences</i><br> +<i>Smithsonian Contributions to the Marine Sciences</i><br> +<i>Smithsonian Contributions to Paleobiology</i><br> +<i>Smithsonian Contributions to Zoology</i><br> +<i>Smithsonian Folklife Studies</i><br> +<i>Smithsonian Studies in Air and Space</i><br> +<i>Smithsonian Studies in History and Technology</i> +</div> + +<p>In these series, the Institution publishes small papers and full-scale monographs that report +the research and collections of its various museums and bureaux or of professional colleagues +in the world of science and scholarship. The publications are distributed by mailing lists to +libraries, universities, and similar institutions throughout the world.</p> + +<p>Papers or monographs submitted for series publication are received by the Smithsonian +Institution Press, subject to its own review for format and style, only through departments of the +various Smithsonian museums or bureaux, where the manuscripts are given substantive review. +Press requirements for manuscript and art preparation are outlined on the inside back cover.</p> + + +<div style="margin-left: 60%"> +Robert McC. Adams<br> +<i>Secretary</i><br> +Smithsonian Institution +</div> +<br> +<br> + + + +<div class="trans_notes"> +<div class="caption2">Transcriber's Notes</div> + +<p>With the exception of the typographical corrections listed below and some minor +changes that may have been made in moving tables or illustrations so that they +are rejoined, the text presented is that published in the original printed media.</p> + +<div class="caption4">Typographical Corrections</div> +<div class="center"> +<table width="86%" summary="typo list"> +<tr><td>Page ii, LOC Data</td><td> : </td><td>Instituion's</td><td> => </td><td>Institution's</td></tr> +<tr><td>Page 1, Introduction</td><td> : </td><td>linages</td><td> => </td><td>lineages</td></tr> +<tr><td>Page 4, The Atypical Procyonid</td><td> : </td><td>consumate</td><td> => </td><td>consummate</td></tr> +<tr><td>Page 21,Summary</td><td> : </td><td>Table 10, footnote f</td><td> => </td><td>Table 10, footnote b</td></tr> +<tr><td>Page 26, first paragraph</td><td> : </td><td>Nassua</td><td> => </td><td>Nasua</td></tr> +<tr><td>Page 31, Literature Cited</td><td> : </td><td>Incoporated</td><td> => </td><td>Incorporated</td></tr> +<tr><td>Page 34, Literature Cited</td><td> : </td><td>Gettleman</td><td> => </td><td>Gittleman</td></tr> +</table> +</div> +</div> + + + + + + + + + + + +<pre> + + + + + +End of the Project Gutenberg EBook of Metabolic Adaptation to Climate and +Distribution of the Raccoon Procyon Lotor and Other Procyonidae, by John N. 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