SPATIAL VARIATION IN ABUNDANCE CREATED BY

A central question in ecology is explaining spatial variation in the abundance of species. Patterns of spatial variation in abundance can often be explained by spatial variation in the environment, including resource availability, climatic variables, and other factors that influence a species' reproduction and survival. We show that spatial patterns in abundance may also be driven by temporal environmental variation, in the absence of any fixed spatial environmental variation. To illustrate this, we build on work by J. H. Brown, D. W. Mehlman, and G. C. Stevens, who demonstrated spatial patterns in bird abundances that can be explained by fixed spatial variation in the environment. Using a pair of simple stochastic models of bird population dynamics, we show that similar patterns can be generated through temporal environmental variation that has no fixed spatial com- ponent. This occurs when population dynamics are characterized by very weak density dependence, so that population densities exhibit near-random-walk behavior. Because sim- ilar patterns of spatial variation in species' abundances can be produced by either fixed spatial environmental variation or spatiotemporal environmental variation, we argue that interpreting spatial variation in abundance may sometimes require understanding temporal variation in abundance.