Effects of mass extinction on beta diversity at nested spatial scales
In the context of the current biodiversity crisis, ecologists are increasingly using the fossil record of mass extinction to interpret current and future patterns of ecosystem collapse. Modern marine ecosystems are showing pronounced spatial (i.e., biogeographic) responses to perturbation, suggesting that the spatial responses of organisms to past mass extinctions may have potential as a valuable interpretive tool. Here, I analyze and contrast the effects of the end-Ordovician mass extinction, which occurred in two separate pulses (~445.2 and ~438.8 million years ago), on patterns of marine beta diversity at local and global scales. Using these data I address the following questions: 1) what are the effects of mass extinction on beta diversity? 2) Are these effects consistent across extinction events with different causal mechanisms? And, 3) Do these effects differ with changing temporal and spatial scale?
I show that both pulses of mass extinction had dramatic effects on global beta diversity, reflected in changing geographic range sizes among marine species. These effects are, however, opposite over the two pulses, revealing stark differences in regional-scale controls on biogeographic patterns associated with each event. Finally, I show that the biogeographic signature of O-S extinction on global spatial scales, and on million year timescales, was dramatically different to what happened on local (~10-100 km) scales over shorter timeframes. This illustrates that the processes sculpting spatial patterns in biodiversity during mass extinctions are scale-dependent. I suggest that these results offer the beginnings of a spatially- and temporally-explicit roadmap for interpreting changing species distributions in the current biodiversity crisis (the ‘6th mass extinction’).