10/27/2025
1. Specialization in Diets:
· A study analyzing stomach contents of 139 terrestrial mammal species found that only 14% (20 species) were true generalists, meaning none of their food resources constituted over 50% of their diet. The majority of mammals were specialized in categories like carnivory, insectivory, herbivory, granivory, or frugivory .
· The term "omnivore" is often avoided in research because many species mix foods but still rely heavily on one primary resource (e.g., insects or fruits) rather than a broad, evenly distributed diet .
2. Quantitative Dietary Studies:
· Large-scale datasets (e.g., covering 82% of extant mammals) classify diets based on taxonomy and macronutrient composition rather than just species counts. These studies highlight that even "mixed" diets often cluster around key food types (e.g., foliage, seeds, or vertebrates) rather than a wide array of species .
· For example, herbivores typically focus on specific plant parts (leaves, stems, fruits), while carnivores target particular prey groups (e.g., vertebrates or invertebrates) .
3. Geographic and Ecological Influences:
· Diets are shaped by food availability, which varies by region. For instance, frugivorous mammals are more common in tropical areas with abundant fruit diversity, while herbivores dominate in temperate or arid zones with fibrous plant matter . This suggests that the number of species in a diet is often constrained by local ecosystem productivity .
4. Exceptions and Variability:
· Some mammals, like bears or pigs, exhibit broader diets, but even these "omnivores" may seasonally specialize (e.g., switching between fruits and insects) rather than consuming many species year-round .
· Marine mammals and bats often have highly specialized diets (e.g., fish or nectar), further reducing the average number of species consumed .
Key Takeaway:
While exact averages are context-dependent, most mammals are not true generalists. Their diets typically revolve around 1–3 dominant food types (e.g., leaves, insects, or vertebrates), with occasional supplementation from other sources. True omnivory—where many species are consumed equally—is rare . For detailed datasets, refer to resources like MammalBase or the EltonTraits database .