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Biodiversityover time
Scudder, G.G.E. (1993). Biodiversityover time, in: Fenger, M.A. et al. (Ed.) Our living legacy: Proceedings of a Symposium on Biological Diversity. pp. 109-1266
In: Fenger, M.A. et al. (1993). Our living legacy: Proceedings of a Symposium on Biological Diversity. The Royal British Columbia Museum: Victoria. ISBN 0-7718-9355-8. XIII, 392 pp.
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| Abstract |
This paper traces the evolution of multi-celled organisms from 600 million years ago to the present. The average annual extinction rate has been about 5 million years per species. There has been a background extinction rate of 9% of species per million years; mass extinctions are defined as at least a doubling of this rate. There have been five major mass extinctions with 50% or more of species losses in some. Several theories for mass extinctions have been proposed, including climatic instability, reversal of the earth's magnetic fields, cosmic radiation from supernovae, asteriod impact and vulcanism. Species survival through an extinction is not linked to success during normal periods and nothing is adapted to survive periodic catastrophic events. Therefore, survivors are lucky, not adaptively superior. The large mammal extinctions in the late Pleistocene (30,000-11,000 years ago) in North America and Australia are linked to the hunting cultures. The large and growing human population is the major cause of current extinctions. Tropical deforestation is a major contributor; at current rates, by the year 2100 there will be a 50% extinction level, similar to the mass extinctions of 66 million years ago when the dinosaurs plus 60-80% of the world's other species were lost. Two significant differences from previous extinctions are the large loss of plants and the persistence of the causal agent (human intervention) following the extinctions. |
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