A major challenge ecologists face is to understand the effects of extreme events for ecological dynamics. Mass mortality events (MMEs) are rare, extreme demographic events, where a large percentage of a population dies within a short time interval. Currently, there is little understanding of the consequences of MMEs for biological communities. Here, we develop a general theoretical framework to understand how MMEs impact the structure and dynamics of communities. To do so, we first build upon existing resource pulse and trophic cascade theory to examine whether MMEs are unique ecological phenomena. We then investigate how the MME magnitude, trophic level of the impacted species, overall food web structure and ecosystem type mediate the resulting ecological response. Finally, we compare the predictions made by our framework to existing observational data on communities impacted by MMEs.
Results/Conclusions:
Our models predict that MMEs are indeed unique ecological phenomena that produce distinct short- and long-term impacts that differ from those following resource pulses or trophic removals. Only when the impact of the dead biomass produced by MMEs on the basal resource is weak do MME and trophic removal transients resemble one another. While MMEs and resource pulses have in common that basal resource abundance initially increases, their transients and equilibria are qualitatively different. MMEs can exhibit unique and potentially volatile dynamics when the dead biomass has an appreciable impact on the basal resource. Our models additionally predict that food webs with higher amounts of omnivory should exhibit more pronounced initial increases in basal resource abundances following MMEs, and that the number of trophic levels present in a food web should lead to different responses due to even-odd effects. General agreement exists between our model predictions and observational reports of MMEs, and mismatches between theory and empirical data highlight directions for future research on MMEs. While complex, resolving the ecological consequences of MMEs should be a high priority for the field of ecology, as it will impact how we manage and conserve biodiversity amidst dynamic environmental change.