Lower elevation animal species do not tend to be better competitors than their upper elevation relatives

Abstract Aim: What factors set species’ range edges? One general hypothesis, often attributed to Darwin and MacArthur, is that interspecific competition prevents species from inhabiting the warmest portions along geographic gradients (i.e., low latitudes or low elevations). A prediction arising from this Darwin-MacArthur hypothesis is that lower elevation species are better competitors than related upper elevation species. An alternative prediction is that upper elevation taxa will tend to be better competitors because they will tend to be larger (Bergmann’s rule). Here, I test these opposing predictions. Location: Global. Time period: 1971 – 2019. Major taxa studied: Birds, mammals, amphibians, fishes. Methods: I conducted a meta-analysis of studies that have measured pairwise behavioral aggression between species-pairs of closely related animals where the two species inhabit divergent elevational distributions. Results: I found that (1) interspecific aggression appears to be a reliabl...