Differences between regional and biogeographic species pools highlight the need for multi-scale theories in macroecology

Abstract

Ecologists are intrigued by the manner in which colonists from a regional pool of species es- tablish and structure local ecological communities. This has initiated several approaches to identifying the relative roles of regional and local processes. Recently, large-scale data sets and novel statistical tools have sparked renewed interest in objectively defined homogeneous species pools. At continental and global scales, these homogenous units are known as biogeographic species pools. Here we argue that the biogeographic species pool is not just a scaled-up version of the regional species pool featured in many foundational ecological theories. Instead, the processes linking local communities and regional species pools differ from those in the biogeographic species pool. To illustrate this, we distinguish be- tween regional and biogeographic species pools by overlaying species distribution data and differentiat- ing between the intersection and union of these distributions. Although patterns in the regional and bio- geographic species pools may appear self-similar across scales, the underlying mechanisms differ from those between local communities and the regional species pool. As a consequence, conventional ap- proaches of quantifying the relative role of local and regional process are inappropriate for studying the biogeographic species pool, thus highlighting the need for new multi-scale theories in macroecology. Keywords. Anura, emergent properties, extent of occurrence, hierarchical spatial scales