Evol Ecol Res 6: 315-337 (2004)     Full PDF if your library subscribes.

Ecological avalanches and the two kinds of extinction

Geerat J. Vermeij*

Department of Geology, University of California at Davis, One Shields Avenue, Davis, CA 95616, USA

e-mail: vermeij@geology.ucdavis.edu


The patterns, causes and consequences of the extinction of species observable today differ from those chronicled in the fossil record. An evaluation of mechanisms of extinction and interpretation of the empirical evidence lead me to argue that competition, predation, invasion and habitat loss – the chief agencies responsible for ecological change and the extinction of species in the human-dominated biosphere today – occur on a relatively small scale, yield few collateral extinctions, and have until now led to species losses mainly among island and lake endemics. By contrast, I argue that the major and minor crises of the geological past were initiated by conditions inhibiting photosynthesis, and that starvation and habitat loss triggered by these conditions led to widespread collateral extinction of species. Conditions traditionally identified by palaeontologists as initiating mass extinction – oxygen deprivation, oversupply of nutrients and poisoning (by carbon dioxide, methane and sulphides) – are interpreted here as manifestations of the ecological avalanche triggered by a crisis among primary producers, and are therefore considered consequences rather than primary causes of extinction. The global trend for habitats to become more island-like and for highly productive environments to be heavily exploited, modified or even eliminated by human activity means that species on larger land masses and in the ocean will become increasingly vulnerable to biological causes of extinction and to further habitat loss. To reduce the biosphere’s vulnerability to the kinds of extinction-generating avalanches chronicled in the fossil record, it is essential to protect species and biogeochemical processes in large, highly productive ecosystems.

Keywords: cascades, extinction, invasion, palaeontology.

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