How temporal turnover in community composition is linked to anthropogenic pressure

Abstract

AbstractUnderstanding the mechanisms behind biodiversity change through time is central to assessing and forecasting anthropogenic impacts on ecological communities. While some local temporal turnover in species composition is natural and indeed underpins ecosystem resilience, it may also indicate external pressure on an ecosystem. Here, we assess how human impacts (via the Human Modification Index synthetic proxy) affect multiple metrics of bird community composition turnover across 2692 transects of the North American Breeding Birds Survey from 27 Bird Conservation Regions over 50 years. Against a background of constant species richness, we find total anthropogenic impact to be consistently associated with greater turnover at long-timescales (reduced asymptotic similarity), but a slightly slower rate of short-term turnover (initial similarity decline). A third turnover measure, the exponent of species accumulation through time, was not notably influenced by humans. Taken together, these results give a new window into ecological community dynamics. In particular, we can identify that intrinsically-driven species turnover is slowed by humans, but turnover determined by extrinsic changes to the ecosystem increases. More widely, our analysis suggests a greater role for intrinsic dynamics in interpreting observed temporal beta-diversity and that anthropogenic impact assessments based on short-term rates of change may be incomplete.