Doctoral Dissertations

Date of Award

8-1998

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Ecology and Evolutionary Biology

Major Professor

Stuart Pimm

Committee Members

Sandy Echtemacht, Mike McKinney, Ken Orvis

Abstract

The world's tropical forests are being cleared extremely fast. At least two-thirds of the world's species are only found in the tropical forests, so this deforestation is causing many species to become extinct. Most of the world's species remain unknown, however. The number of extinctions that have been witnessed is hence very low. In this dissertation I attempt to reconcile the high levels of extinction predicted from deforestation with the low numbers of extinctions actually observed. First, I compare the number of bird extinctions that we would predict will occur based on the extent of deforestation with the number of species considered threatened in the Red List. I do this for both the islands of South-east Asia and for the Atlantic forests of South America. In both cases I show that tropical deforestation causes extinctions that are not only numerous but also predictable. Second, the fact that the extent of deforestation predicts the number of species that are threatened rather than the number of extinctions that have already occurred indicates that there is a time lag between deforestation and extinction. I address the question of how long this is through an intensive study of Kakamega rainforest, Kenya. I find that, for forests of c. 1,000 ha (the scale at which conservation and management typically operate) about half of the species likely to be lost in total will have become extinct after only 50 years. Most will have become extinct by a century. This is the window of opportunity that we have to conserve of rainforest biodiversity.

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