How resource abundance and stochasticity affect organisms’ range sizes

Abstract

The amount of space organisms use is thought to be tightly linked to the availability of resources within their habitats, such that organisms living in productive habitats generally require less space than those in resource-poor habitats. This hypothesis has widespread empirical support, but existing studies have focused primarily on responses to themeanamount of resources, while responses to the variance around the mean are still largely unknown. This is not a trivial oversight. Organisms adjust to variable environmental conditions, so failing to consider the effects of resource (un)predictability can result in a limited understanding of organisms’ space-use requirements, challenging ecological theory and applied conservation alike. In this study, we first review the literature of studies that estimate organisms’ spaceuse requirements as a function of resource abundance. We then leverage this information to provide a unifying framework and hypotheses for the effect of meanandvariance in resources on organisms’ space use. Next, we use simulated movement data to demonstrate how the combined effects of mean and variance in resource abundance interact to shape predictable patterns in space use. Finally, we use real-world tracking data on a lowland tapir (Tapirus terrestris) from the Brazilian Cerrado to show how this framework can be applied to better understand the movement ecology of free-ranging animals. Results from the simulations and empirical examples are presented using a fully transparent approach that allows researchers to apply the framework to their own data and inform area-based conservation efforts.