next up previous

1 Introduction

Since the Endangered Species Act was passed in 1972, approximately 800 species have been listed as threatened or endangered. About 400 more are deemed to be in immediate danger, but there are insufficient resources to carry out the studies necessary for listing, and there are another 3500 species with credible proposals for listing.

A key part of the decision as to whether to list a species as threatened or endangered rests on a population viability analysis, in which teams of scientists from various disciplines try to determine the probability of extinction as a function of three different types of parameters: