Temporally robust occupancy frequency distributions in riverine ecosystems explained by local biodiversity regulation

Abstract

The mechanisms determining the distribution of the number of sites species occupy--the occupancy frequency distribution (OFD)--remain incompletely understood despite decades of research. Here we study OFD in fresh-water metacommunities in England. We show that OFD are largely time invariant despite continuous turnover in community composition and well described by log-series distributions. Both shape and temporal robustness are readily explained by a simple patch occupancy model with intrinsic regulation of local richness. The model is mathematically analogous to classical neutral theory, but concerns numbers of patches occupied instead of individuals present. The precise shape of the models log-series OFD is determined by a parameter representing the rate of colonisation from adjacent sites, which we estimate for the data. Our results support the view that meta-community structure reflects a dynamic steady state controlled by local ecological constraints. Interspecific trait differences underlie these constraints, but are unlikely to determine macroecological structure.