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Abstract.-
Extinction in the fossil record is most often measured by the percentage of taxa (species, genera, families, etc.) that go extinct in a certain time interval. This is a measure of taxonomic loss, but previous work has indicated that taxonomic loss may be decoupled from the ecological effects of an extinction. To understand the role extinction plays in ecological change, extinction should also be measured in terms of loss of functional diversity. This study tests whether ecological changes increase correspondingly with taxonomic changes during the Late Ordovician M4/M5 extinction, the Ordovician/Silurian mass extinction, and the Late Devonian mass extinction. All three extinctions are evaluated with regional data sets from the eastern United States. Ecological effects are measured by classifying organisms into ecological lifestyles, which are groups based on ecological function rather than evolutionary history. The taxonomic and ecological effects of each extinction are evaluated with additive diversity partitioning, detrended correspondence analysis, and relative abundance distributions. Although the largest taxonomic changes occur in the Ordovician/Silurian extinction, the largest ecological changes occur in the Late Devonian extinction. These results suggest that the ecological consequences of extinction need to be considered in addition to the taxonomic effects of extinction.
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Introduction
The fossil record contains numerous episodes of elevated extinction ranging in scale from the "big five" mass extinctions (Raup and Sepkoski 1982) to smaller, often regional events, such as the early Late Ordovician (M4/M5) event (Holland and Patzkowsky 1996; Patzkowsky and Holland 1996). Most extinction studies primarily measure changes in taxonomic diversity (e.g. Raup and Sepkoski 1982; Jablonski 1986; Sepkoski 1993; Benton 1995; Foote 2003; Alroy 2008), but these changes might not reflect the degree of disruption in ecosystem functioning (Ricklefs and Schlüter 1993; Droser et al. 1997). Although ecological changes across extinction events have been considered (e.g., Boucot 1983; Bottjer and Ausich 1986; Watkins 1993; Sheehan 1996; Todd et al. 2002; Jackson and Erwin 2006, Villéger et al 2011), fewer studies have explicitly contrasted taxonomic loss and the ecological effects of extinction. Several of these studies have shown that ecological changes do not always mirror the level of taxonomic loss experienced from an extinction event (Plotnick and McKinney 1993; Roy 1996; Droser et al. 1997, 2000; McGhee et al. 2004).