Food Habits of Procyonids.—Food habits of six procyonids for which metabolic data are available are presented in [Table 9]. All six species clearly have mixed diets. Compared to other species, Procyon lotor is highly catholic in its diet, taking food from almost twice as many categories as Nasua narica, three times as many as Procyon cancrivorus, Nasua nasua, and Bassariscus astutus, and nine times as many as Potos flavus.
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 ([Table 9]).
1. Potos flavus: (1) arboreal/frugivore, insectivore.
2. Procyon cancrivorus: (1) semiaquatic/crustacivore, molluscivore, insectivore, piscivore, carnivore.
3. Nasua nasua: (1) terrestrial/insectivore, arachnidivore, carnivore, frugivore.
4. Bassariscus astutus: (1) terrestrial/carnivore, insectivore, frugivore.
5. Procyon lotor: (1) terrestrial/carnivore, granivore, frugivore, insectivore; and (2) semiaquatic/crustacivore, molluscivore, insectivore, piscivore, carnivore.
Food Habits and Basal Metabolism.—The most important foods in the diet of Procyon lotor are vertebrates, nuts, seeds, and fruits ([Table 9]). These are the same foods that are eaten by those dietary specialists that have Ḣb's equivalent to, or higher than, values predicted for them by the Kleiber equation (McNab, 1986a). The most important foods in the diets of Potos flavus, Procyon cancrivorus, and Nasua nasua are invertebrates and fruit ([Table 9]), and these foods are eaten by dietary specialists that have lower than predicted Ḣb's (McNab, 1986a). Major foods in the diet of Bassariscus astutus are terrestrial vertebrates, insects, and fruit ([Table 9]). Dietary specialists that eat terrestrial vertebrates have higher than predicted Ḣb's, whereas those that feed on insects have Ḣb's that are lower than predicted (McNab, 1986a). Year-round utilization of vertebrates by Bassariscus astutus 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 Ḣb than do vertebrates in its diet.
Summary.—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 ([Table 7]) suggest that lower than predicted Ḣb 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 Ḣb, whereas food habits would have had a secondary influence.