COS 123-2
Animal mass mortality events in nature
All organisms eventually die. However, the patterns of and processes surrounding death vary tremendously. Mortality occurring on daily, seasonal, and annual timescales can be punctuated by larger mass mortality events (MMEs), which may quickly exterminate large numbers of individuals. Individual MMEs are staggering in their magnitude—removing over 90% of a population, resulting in the death of over a billion individuals, or producing 700 million tons of dead biomass in a single event.
Despite the extensive documentation of such individual MMEs, no synthetic, quantitative analysis has examined patterns of MMEs across the animal kingdom. Consequently, no framework exists for contextualizing MMEs in a wake of ongoing global and regional perturbations to natural systems, which may be driving the occurrence of MMEs. Here we assemble and analyze a database of 1184 published MMEs from 460 studies to address a number of outstanding questions: 1) Has the occurrence of MMEs changed through time? 2) Has the magnitude of MME’s changed through time? 3) What are the putative causes of MMEs?
Results/Conclusions
We show that since at least 1940 MMEs are occurring more frequently with time, although publication bias may hinder this interpretation. The documented increased frequency of MMEs is also accompanied by a shift in the magnitude of MMEs: increasing for birds, fish, and invertebrates, but not for reptiles, amphibians, or mammals. While difficult to resolve with current data sets, the increase in MMEs appears to largely be associated with disease and biotoxicity.
Given the ability of MMEs to disrupt ecosystem services and the fact that humans are not immune to MMEs, nor their effects, effective monitoring and analysis of MMEs remains a critical component of anticipating and attempting to mitigate future MMEs.