MODELS OF RECOVERY DYNAMICS FOLLOWING MASS EXTINCTION

Biotic recoveries following mass extinctions are characterized by a complex set of dynamics, including the reconstruction of whole ecologies from low-diversity assemblages of survivors and opportunistic species. Three broad classes of diversity dynamics during recovery have been suggested: an immediate, linear response, a logistic recovery, and a positive feedback pattern of species interaction. Past models have focused on logistic recovery and on the re-filling of ‘empty niches’ purportedly vacated by mass extinction. Such models suffer from several difficulties. First, logistic models externally impose a carrying capacity, while the sort of process models we seek would allow the carrying capacity to evolve based on model parameters. Second, while un- or under-utilized resources may exist after biotic crises, empty niches are fictitious. The critical issue for biotic recovery is how new niches are constructed, not refilled, and this suggests a fundamental dichotomy between some biotic crises and smaller scale ecological disasters where niche refilling may be operating. Here we present the simplest model of recovery generating the qualitative differences between the three patterns and suggest the ecological processes underlying them. This simple model of diversification is driven by biotic interactions between pairs of species, and is a first effort at examining the relevance of positive feedback processes in such evolutionary diversifications. In these models we consider the equilibium case where diversity returns to the pre-extinction level. In reality, the most interesting cases are those where post-extinction diversity increases. These models suggest the nature of data paleontologists must collect to test alternative, process models of biotic recovery.