Codistribution as an indicator of whole metacommunity response to environmental change.
Metacommunity structure can be summarised by fitting joint species distribution models and partitioning the variance explained into environmental, spatial and codistribution components. Here we identify how these components respond through time with directed environmental change and propose this as an indicator of sustained directional pressure. Through simulations, we identify how declines in the codistribution component can diagnose ecological breakdown, while rises in environmental and spatial components may indicate losses in peripheral areas and dispersal limitations. We test the method in two well-studied systems. Butterflies are known to be strongly responding to climate change, and we show that over 21 years the codistribution component declines for butterfly communities in southern England. By contrast, birds in the same region are under less climate pressure and, despite high occupancy turnover, show minimal change in metacommunity structure. The approach has high potential to summarise and compare the impact of external drivers on whole communities.