Change in community composition is emerging as the most evident way in which biodiversity is changing in the Anthropocene. Extinctions and colonizations, as well as changes in relative abundances of populations drive temporal turnover in ecological communities, and affect spatial patterns in β diversity. We used biodiversity time series in the bioTIME database to dissect ecological turnover within and across communities, in space and time and across taxa.
We found that colonizations and extinctions are balanced in the time series in our database and are rare. The vast majority of populations are either transiently detected (with random sequences of presences and absences), or always present. Most populations have no detectable trend in their abundances. The populations with detectable trends are equally divided among those increasing and those decreasing in abundance. Temporal turnover in ecological communities is therefore the result of a balance between winners and losers, which can be identified as particular species. Compositional changes are also reflected in spatial β diversity patterns, with some communities undergoing biotic homogenization, while others are becoming more dissimilar through time.