Prey resources are more important than climatic conditions for predicting the distribution of a broad-ranged apex predator

A current biogeographic paradigm states that climate regulates species distributions at continental scales and that biotic interactions are undetectable at coarse-grain extents. However, recent advances in spatial modelling show that incorporating food resource distributions are important for improving model predictions at large distribution scales. This is particularly relevant to understand the factors limiting distribution of widespread apex predators whose diets are likely to vary across their range. The harpy eagle (Harpia harpyja) is a large raptor, whose diet is largely comprised of arboreal mammals, such as sloths and primates, all with broad distributions across Neotropical lowland forest. Here, we used a hierarchical modelling approach to determine the relative importance of abiotic factors and prey resource distribution on harpy eagle range limits. Our hierarchical approach consisted of the following modelling sequence of explanatory variables: (a) abiotic covariates, (b) prey resource distributions predicted by an equivalent modelling for each prey, (c) the combination of (a) and (b), and (d) as in (c) but with prey resources considered as a single prediction equivalent to prey species richness. Incorporating prey distributions improved model predictions but using solely these biotic covariates still resulted in a high performing model. In the Abiotic model, Climatic Moisture Index (CMI) was the most important predictor, contributing 80 % to model prediction. Three-toed sloth (Bradypus spp.) was the most important prey resource, contributing 57 % in a combined Abiotic-Biotic model, followed by CMI contributing 29 %. Harpy eagle distribution had moderate to high environmental overlap across all prey distributions in geographic space when measured individually, but overlap was substantially lower in environmental space when prey distributions were combined. With strong reliance on prey distributions across its range, harpy eagle conservation programs must therefore consider its most important food resources as a key element in the protection of this threatened raptor.