Historical legacies accumulate to shape future biodiversity in an era of rapid global change

Aim Biodiversity responses to changing environmental forcing on species are often characterized by considerable time-lags (= relaxation times). Although changes to the occurrence and abundance of species likely have cascading effects (e.g. on species of other trophic levels, genes, community structure and ecosystem processes), current concepts addressing lagged biodiversity responses are limited to single drivers affecting a few biodiversity components (e.g. extinction debt in terms of species numbers or population size). Little attention has been paid to the interacting and cumulative nature of time-lag phenomena. Here, we synthesize current knowledge, mechanisms and implications of delayed biodiversity responses and propose a ‘cumulative biodiversity lags-framework’ which aims to integrate lagged responses of various components of biological organization. Location Global. Results Effects of change in environmental forcing are transmitted along a series of linked cause–effect relationships which act on different biodiversity components (e.g. individuals, populations, species, communities). We show that lagged responses to environmental forcing are caused by different mechanisms (e.g. metapopulation dynamics, dispersal limitation, successional dynamics), which operate sequentially on these intermediary links. Lags manifest themselves on the respective biodiversity component which changes over time; the full relaxation time of a focal system will therefore depend on the aggregate length of different lags. We elucidate key mechanisms and circumstances which are likely to cause cumulative lagged responses, and propose research avenues to improve understanding of cumulative biodiversity lags. Main conclusions The failure to give adequate consideration to widespread cumulative time-lags often masks the full extent of biodiversity changes that have already been triggered. Effects that are particularly relevant for human livelihoods (e.g. changes in the provision of ecosystem services) may emerge with the most pronounced delay. Accordingly, the consideration of appropriate temporal scales should become a key topic in future work at the science–policy interface