DIET AND BODY MASS IN TERRESTRIAL MAMMALS


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FIGURE 4. Geographical distribution of tropical and subtropical moist broadleaf forests (adapted from Olson et al. [2001]) and of pure frugivore and mixed frugivore species in our data set (extracted from Map of Life [2016]).


to support their populations. Instead, they specialize their feeding on vegetation, a much more abundant food resource. Our results support this idea and show how dietary diversity decreases with increased body mass as a general trend. Having lower requirements for energy and nutrients per unit of body weight allows large mammals to feed on less nutritive resources (i.e., structural plant material) and get most of their nutrients from a very specialized diet (Demment and Van Soest 1985; Clauss et al. 2007, 2013). Increased body size allows herbivores to evolve gut structures that increase volume and retention time of the ingesta, and so they are capable of extracting a higher fraction of nutrients from low-energetic plant materials (i.e., leaves and grasses). However, it has been observed that long retention times are not characteristic of very large mammals. In those cases, other ecological advantages such as larger home ranges, predator avoidance, or resource competition are a potential benefit of large body size (Clauss et al. 2007, 2013; Steuer et al. 2014). Most micromammals (<10g) in the data set


display a rather specialized insectivorous diet. Their high metabolic costs require them to feed on food resources with substantial energy content such as insects (Peters 1986).


Additionally, their small size might mechani- cally restrict their diets to small invertebrates (Fisher and Dickman 1993). Thus, it could be postulated that extreme body sizes require higher levels of specialization and that the optimum for a very diverse diet must lie in the small range (10–999 g) (Raia et al. 2012), as it does.


Among predators (pure insectivores and


carnivores), the maximum body mass for the insectivores in our data set is 8.5 kg, with larger predators being carnivores. Similarly, Carbone et al. (1999) estimated a maximum sustainable mass of 21.5 kg for invertebrate diets, although some exceptionally larger insectivore mammals such as the aardvark (Orycteropus afer, 52 kg) do exist. Additionally, the average size of the pure insectivore mammals in Wilman et al. (2014)—the biggest data set known so far—is 914 g. Previous research suggested that myrmecophagous mammals from Afrotropical forests seemed to have the lowest population densities. Thus, resource availability might be limiting the maximum body mass of insectivores. As mentioned, the maximum degree of food


mixing tends to decrease with increasing body mass. However, the brown bear U. arctos falls outside this pattern according to the dietary diversity statistic. Surviving hibernation


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