Global climate change has often resulted in extinction events that can be quantitatively measured by taxonomic loss but are more difficult to assess in terms of ecological restructuring. We use a commonly applied ecological tool, rank-abundance curves (RACs), to evaluate the ecological response of benthic foraminiferal and ostracode communities to the Paleocene-Eocene thermal maximum, which may be seen as an analog for current and future global warming. RACs are proxies for community structure, and therefore changes in the shape of RACs allow inferences to be drawn about and quantification of ecological responses. Benthic foraminiferal communities became increasingly stressed during the Paleocene-Eocene thermal maximum, and community reorganization occurred before the taxonomically defined extinction horizon. In contrast, ostracode communities became less stressed during the same interval, reinforcing the idea that different groups of organisms respond differently to extinction events and global warming. The decoupling of ecologic impact from taxonomic impact during the Paleocene-Eocene thermal maximum reaffirms the fact that future climate change could have far-reaching effects on taxa and ecosystems and proves the importance of examining both the taxonomic and ecologic responses of communities during extinction events.

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