Abstract

Alternative ecological theories make divergent predictions about the relationship between predators and their prey. If predators exert top-down ecosystem control, increases in predation should diminish prey abundance, but can alternatively diminish or enhance community diversity of prey species. But if bottom-up ecosystem controls predominate, variation in predation should track underlying variation in prey diversity and abundance, which ultimately should reflect available energy. Past research, both across islands, and comparing islands with the mainland have frequently invoked the importance of predator occurrence in regulating lizard abundance and diversity, suggesting an important role of top-down control when predators are present. However, others have posited a stronger role of food limitation, either by way of competition or bottom-up forces. If top-down control predominates generally, then negative correlations between prey abundance and predator occurrence should emerge within islands, as well as across islands. Using survey data from eBird, we inferred landscape-level bird presence for all species on the islands of Jamaica and Hispaniola. By summing occurrence probability of known anole-predator birds we estimated total avian predation pressure and combined these estimates with anole community data from a mark-recapture study that spanned spatial and climatic gradients on both islands. Avian predators and anole lizards were both affected by climate, with total predation pressure, as well as anole abundance and species richness increasing with mean annual temperature. While predator occurrence was uncorrelated with anole abundance, it was positively correlated with anole species richness. These findings suggest that despite past research showing that islands with more predators tend to have lower abundances of prey, within islands, top-down forces of predation may not be strongly limiting community diversity. Instead, bottom-up forces linked with climate may be more important drivers of diversity in both lizards and their avian predators.