Diversity Regulation in Local Communities: Colonization and Extinction Dynamics in North American Birds

ABSTRACT Aim Species richness of local communities may be regulated via negative diversity dependence of colonization or positive diversity dependence of extinction rate. We explore whether and how bird communities are regulated and what determines extinction and colonization rates across communities. Location North America, spanning the United States and Canada. Time Period 1995–2019. Major Taxa Studied Passerines. Methods We used long‐term community time‐series from the North American Breeding Bird Survey (BBS) to analyse spatial patterns in colonization and extinction rates across 646 survey routes. We linked these rates to community species richness, proportion of species pool represented in the local community, richness relative to resource level, mean population size and stability and environmental productivity and its seasonality (approximated by Normalized Difference Vegetation Index, NDVI). We used correlation analyses, generalized linear models, Random Forest and Structural Equation Modelling (SEM). Results Extinction and colonization rates are highly balanced across sites, supporting the idea of diversity regulation. Both rates are lower at sites with higher equilibrium species richness and especially at sites with a higher proportion of the species pool represented in the local community, supporting the diversity‐dependence of colonization rate. In contrast, we did not find any evidence for local diversity‐dependence of extinction rate. However, extinction rates increase with decreasing population sizes of species and are negatively affected by environmental productivity that influences population stability. Main Conclusions Local bird community richness appears regulated, but this regulation stems primarily from a progressive exhaustion of the number of potential colonists from a species pool as local species richness increases, not from a decreasing population size with increasing richness. Local bird diversity is then determined by the interaction of the size of the species pool with local population persistence modulated by environmental productivity. Diversity dynamics is thus essentially equilibrial, but regional and local diversity appear regulated by different mechanisms.