SMITHSONIAN INSTITUTION PRESS
Washington, D.C.
1993

Mugaas, J. N., J. Seidensticker, and K. Mahlke-Johnson. Metabolic Adaptation to Climate and Distribution of the Raccoon Procyon lotor and Other Procyonidae. Smithsonian Contributions to Zoology, number 542, 34 pages, 8 figures, 12 tables, 1993.—Although the family Procyonidae is largely a Neotropical group, the North American raccoon, Procyon lotor, 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 Procyon lotor evolved a different set of adaptations that have enabled it to generalize its use of habitats and climates. To test this hypothesis we compared Procyon lotor with several other procyonids (Bassariscus astutus, Nasua nasua, Nasua narica, Procyon cancrivorus, and Potos flavus) with respect to (1) basal metabolic rate (Ḣ_b), (2) minimum wet thermal conductance (C_mw), (3) diversity of diet (D_d), (4) intrinsic rate of natural increase (r_max), and, where possible, (5) capacity for evaporative cooling (E_c). We measured basal and thermoregulatory metabolism, evaporative water loss, and body temperature of both sexes of Procyon lotor 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.

Procyon lotor differed from other procyonids in all five variables. (1) Procyon lotor's mass specific Ḣ_b (0.46 mL O₂·g^-1·h^-1) was 1.45 to 1.86 times greater than values for other procyonids. (2) Because of its annual molt, Procyon lotor's C_mw was about 49% higher in summer than winter, 0.0256 and 0.0172 mL O₂·g^-1·h^-1·°C^-1, respectively. The ratio of measured to predicted C_mw for Procyon lotor in winter (1.15) was similar to values calculated for Potos flavus (1.02) and Procyon cancrivorus (1.25). Values for other procyonids were higher than this, but less than the value for Procyon lotor (1.76) in summer. On a mass specific basis, Bassariscus astutus had the lowest C_mw with a ratio of 0.85. (3) Procyon lotor utilized three times as many food categories as Procyon cancrivorus, Nasua nasua, and Bassariscus astutus; about two times as many as Nasua narica; and nine times as many as Potos flavus. (4) Intrinsic rate of natural increase correlated positively with Ḣ_b. Procyon lotor had the highest r_max (2.52 of expected) and Potos flavus the lowest (0.48 of expected). The other procyonids examined also had low Ḣ_b, but their r_max'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_b and elevated r_max. (5) Although data on the capacity for evaporative cooling were incomplete, this variable appeared to be best developed in Procyon lotor and Bassariscus astutus, the two species that have been most successful at including temperate climates in their distributions.

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. Procyon lotor had the highest composite score (1.47) and Potos flavus 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.

It was clear that Procyon lotor 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_b that is higher than the procyonid norm appears to be the cornerstone of its success.

Official publication date is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. Series cover design: The coral Montastrea cavernosa (Linnaeus).

Library of Congress Cataloging-in-Publication Data
Mugaas, John N.
Metabolic adaptation to climate and distribution of the raccoon Procyon lotor and other Procyonidae / John N. Mugaas, John Seidensticker, and Kathleen P. Mahlke-Johnson.
p. cm.—(Smithsonian contributions to zoology; no. 542)
Includes bibliographical references (p.       )
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.
QL1.S54 no. 542 [QL737.C26] 591 s-dc20 [599.74´443´04542] 93-3119

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.