Introduction

Species may, in principle, respond to environmental change in several different ways (Pease et al. 1989; Holt 1990; Chapters 10 and 11). Some species may track environmental states to which they are already well adapted and so shift in abundance and distribution. Other species may not evolve at all and so become extinct. Some species may evolve adaptively in ways that facilitate their persistence in changed environments. Yet other species may evolve in ways that hamper their long-term viability. A fundamental goal of the discipline of evolutionary conservation biology is to understand the factors that govern the relative likelihood of each of these outcomes.

Recognizing the importance of directional environmental change in driving extinctions in once-common species raises a profound puzzle. On the one hand, as ecologists we know that extinction risk emerges because directional environmental changes lead to lowered population abundances and/or restricted distributions; in effect, species are pushed outside their niches. On the other, as evolutionists we know that species often have abundant genetic variation, and so can adapt to novel circumstances. Conservation problems arise precisely because species do not adapt sufficiently to the new environments created by anthropogenic activity. In other words, conservation problems reflect a seeming failure of evolution by natural selection to adapt species to environmental change.

Such failures are examples of “niche conservatism”.