A Paradigm for Population Analysis of Long-Lived Vertebrates

Abstract

A sequence of changes in vital rates observed as populations approach maximal levels has been used as the basis for a “paradigm” for population analysis. Previous work indicates that early survival decreases first, followed by lower reproductive rates; ultimately, adult female survival may decrease. “Sensitivity” of population growth rates, as measured by partial derivatives of an approximation to the Lotka-Leslie model, appears to follow the same sequence, suggesting that population regulation may follow that sequence. This may imply some evolutionary significance in the sequence. Thus, it may be possible to assess population status by measuring the vital rates, as shown in a number of examples reported here. Measuring vital rates in the field is subject to a variety of biases; hence, an analysis should include direct estimates of population trend. In the absence of complete data, suitable trend data might be used to estimate missing rates. Bootstrapping provides a simple way to obtain confidence intervals, and the delta method can be used to obtain components of variance and thus improve sampling. Various methods for studying trend are given, with examples and simple statistical tests.