Abstract
Species Abundance Distributions (SADs) are one of the strongest generalizations in community ecology, but their variation across trophic levels remains largely unexplored. I study the variation in SAD metrics across trophic guilds in model and empirical communities. First, I use a theoretical model that allows tracking the variations in abundances across trophic levels, accounting for variations in species vulnerability. Second, I compare the empirical SADs of 226 terrestrial plant communities and 497 mammal communities comprising species of three general trophic guilds (herbivores, omnivores, and carnivores). I analyze the differences in evenness and skewness of the empirical SADs across the different trophic guilds, controlling for species richness, spatial and temporal resolution of the sampling. In model communities, consumer guilds have significantly more even and less skewed SADs than producers. Increasing vulnerability, i.e. the number of predators per prey, also increases consumer evenness and decreases skewness. In empirical datasets, plant communities are significantly less even and more skewed than mammal ones. There are no significant differences in SAD metrics between the different mammal guilds, but carnivores are comparatively rare (i.e. have a higher proportion of species than individuals), whereas omnivores are comparatively more common. Species richness has a positive effect on both evenness and skewness, and spatial and temporal extent have negative effects on evenness and do not affect skewness. I argue that the difference between plant and mammal guilds can be related to higher niche availability in animals than in plants. As no systematic differences were found between the SADs of mammal herbivores, omnivores, and carnivores, this may indicate similar niche availability, when averaged across habitat types, for the different animal trophic guilds.
