Does ecological change scale with percent extinction?

Abstract

Extinction in the fossil record is most often measured in terms of the percent of taxa (species, genera, families, etc.) that go extinct across a certain time interval. While this measures the taxonomic effects of extinction, previous work has indicated that these may be decoupled from the ecological effects of an extinction. In order to understand the role extinction plays in ecological change, extinction needs to be measured in terms of functional diversity as well. This study quantifies whether the ecological intensity of extinction scales with the taxonomic intensity across the M4/M5 extinction in the Late Ordovician, the Late Devonian mass extinction, and the Ordovician-Silurian mass extinction. Taxonomic and ecological signals are measured by classifying organisms into genera and guilds, a method of grouping organisms based on their ecological function, not their evolutionary history. The taxonomic and ecological effects of each extinction are evaluated with additive diversity partitioning, detrended correspondence analysis, and relative abundance distributions. The results of this study show that the largest taxonomic changes occur across the Ordovician-Silurian extinction and the largest ecological changes occur across the Late Devonian extinction. In terms of ecological selectivity, both the Late Devonian and M4/M5 were more selective than the Ordovician-Silurian. These results suggest taxonomic intensity of an extinction is a poor predictor of the ecological disruption caused by that extinction.