Modeling the Demographic Effects of Endocrine Disruptors

In this article we describe a series of strategic models of populations and individuals subject to challenge by endocrine disruptors. These models are not designed to be fitted to detailed data on specific species but rather are intended to provide general insights on the relative importance of different demographic mechanisms in the population context. Therefore, the models contain the minimum necessary biological detail, but in recompense they are highly accessible to mathematical analysis. We show that, over a range of models with contrasting biological detail, population viability is controlled by the number of female offspring that result from the average female's lifetime reproductive activity. Thus, male fertility changes have little effect at the population level until they become severe enough to reduce this average female output. We argue that in many circumstances endocrine disruptors are likely to produce directly deleterious effects on female fecundity at levels far below those required to reduce male fertility to dangerously low levels. Finally, we formulate a simple model of individual energetics that we argue can form the basis of a strategic discussion of the likely sensitivity of female demographic parameters to chemically induced changes in physiological function.