Geographically-Structured Populations and Migration-Extinction Equilibria

Abstract

In the two previous chapters we have primarily considered population interactions under the tacit assumption of homogeneous environments and it was possible to arrive at theoretical conclusions which give insight in many observations from nature. Yet, nature seldom consists of homogeneous environments but must often be described as a heterogeneous mosaic of more or less isolated habitat patches each harboring larger or smaller populations, with migration between them. This structure has to be taken into account when a complete description of ecosystems is attempted. Such considerations lead to conclusions which in part differ qualitatively from those arrived at in the previous chapters. However, there is no contradiction between the two ways of looking at biological communities. Rather it is a question of scale; within each habitat patch the mechanisms outlined in the previous chapters are believed to function. But the interaction between a larger number of more or less isolated environmental patches interconnected by low rates of migration will result in systems with special, and in many ways, complex features.