Oecologia (Berlin) (1985) 67:540-554 Oecologia 9 Springer-Verlag 1985 Carnivore body size: Ecological and taxonomic correlates John L. Gittleman* School of Biological Sciences, University of Sussex, Brighton, U.K., and Department of Zoological Research, National Zoological Park, Smithsonian Institution, Washington, DC 20008, USA Summary. Variation in body size (weight) is examined across the order Carnivora in relation to taxonomy (phylo- geny), latitude, habitat, zonation, activity cycle, diet, prey size, and prey diversity. Significant differences in body weight are observed with respect to family membership. Some of these differences may be explained by phylogenetic history and/or dietary effects. Body weight is not correlated with habitat, zonation, activity cycle or latitudinal gra- dients. Significant differences in body weight are found among insectivorous, herbivorous and carnivorous species, and some of these differences may relate to energetic con- straints. Among predatory carnivores, prey size and diver- sity increases with body weight. The adaptive significance, both intra- and inter-specifically, of prey characteristics (size, availability, diversity) and carnivore body weight qua- lities (strength, endurance, hunting technique) is discussed. The range of body sizes found in the order Carnivora is unparalleled in any other mammalian order (Savage 1977; Bekoff et al. 1984). Differences in body size are often asso- ciated with variation in life histories (Eisenberg 1981; Calder 1984), metabolic rate (Kleiber 1961; McNab 1980), population group size (Clutton-Brock and Harvey 1977), and various ecological factors (Bourlibre 1975; Fleagle 1978; Searcy 1980; Clutton-Brock and Harvey 1983). This paper examines some of the selective forces that have possi- bly influenced carnivore body size. The following introduc- tory comments discuss those hypotheses which are directly relevant to carnivore body size, and some of them are tested using the existing comparative data. Metabolic Rate. Basal metabolic rate (volume of oxygen metabolized per unit body weight) scales to the 0.75 power of body weight (Kleiber 1961). The reason(s) for this allo- metric relationship remain unclear; however, the impor- tance of scaling is reflected by the rates at which different animals process food (Geist 1974; Jarman 1974; Clutton- Brock and Harvey 1977; Martin 1979). In general, a higher metabolic rate per unit body weight in small mammals is * Present address: Department of Zoology, University of Tennes- see, Knoxville, TN 37916, USA associated with a need to select food that is high in nutri- tional value and energy content. Larger-bodied mammals, by contrast, can feed on foodstuffs that are low in energy content and slow to release energy during digestion (for review see McNab 1980). For example, small primates typi- cally feed on a mixture of animal prey (mainly arthropods) and plants rich in carbohydrates (e.g., gums, fruit) whereas folivorous habits are mainly found in primates of moderate to large size (Clutton-Brock and Harvey 1977). This, of course, assumes that larger animals can behaviorally obtain and ingest proportionately more food (Clutton-Brock and Harvey 1983). It is important to recognize, however, that this pattern is relative rather than absolute: for example, although browsing ungulates tend to be smaller than graz- ing species (Jarman 1974), they are nearly all larger than grazing rodents (Mace 1979). Thus, the taxonomic level of analysis is a critical factor in teasing apart relationships of size, diet and energy requirements. Climate. The most widely known climatic or ecogeograph- ical rule is Bergmann's rule which states that "races from cooler climates tend to be larger in species of warm-blooded vertebrates than races of the same species living in warmer climates" (Mayr 1963). Recent discussion has also shown that Bergmann's rule may apply across species (Barnett 1977; James 1970). The interpretation and validity of Berg- mann's rule has received much attention (Huxley 1942); Scholander 1955; Irving 1957; Mayr 1963; Rosenzweig 1968; McNab 1971) and many causal explanations have been given for the observation that within related taxa in- creases in body size occur in cooler climates. In general, these explanations relate to thermoregulation (Bergmann 1847), latitudinal changes in food or prey size and conse- quential increases in competition (McNab 1971), or season- ality at different latitudes (Boyce 1979; Searcy 1980). Despite little agreement on the functional reasons for latitudinal change in body size (see Clutton-Brock and Har- vey 1983), empirical observations support the relationship in various genera of small mammals (Neotoma: Brown and Lee 1969; Citellus, Lepus and Peromyscus: Mace 1979), carnivores (Vulpes: Davis 1977) and birds (Kendigh 1969). Differences in body size across Carnivora have not been studied in relation to latitudinal variation. Diet. Body size clearly sets limits on the size, range and selectivity of food an animal can exploit, Smaller animals