The role of extinction in large-scale diversity-stability relationships

More-diverse communities are thought to be ecologically stable because a greater number of ecological interactions among members allows for the increases in robustness and resilience. Diversity-stability relationships have mostly been studied on short ecological time scales but one study has identified such patterns over million-year time scales in reef communities. Here we propose and test a hypothesis for the mechanism of large-scale diversity-stability relationships in reefs. The extinction of community members destabilizes the community as a whole, unless there is sufficient diversity to buffer the community from the stochastic loss of members, thereby preventing collapse. If genera have high extinction rates, any variation in diversity among communities will result in a diversity-stability relationship. Conversely, in the absence of other mechanisms, the stability of low extinction communities is expected to be independent of diversity. We compare the extinction rates of six reef-building metazoan taxa to patterns of reef community stability and reef volume. We find that extinction of reef-builders occurs independent of reef volume, and that the strength of the diversity-stability relationship varies positively with extinction rate.