Succession: An Evolutionary Interpretation

An evolutionary interpretation of succession includes the following points. First, in order for a population to be well adapted to a particular set of conditions, it cannot be adapted to many different sets. There is an apparent limit to the width of niche and of habitat that a population can exploit effectively. Selection preserves these unique adaptations and fosters population coupling with the environment. Second, succession provides a complex gradient of physical and biotic environments, analogous to spatial gradients, to which species respond in both ecological and evolutionary time. Selection adjusts the positions of populations on successional gradients in the same way they are adjusted on spatial gradients. Third, the evolutionary strategy, which involves life-cycle length, time of reproduction, reproductive output, and ultimately the degree of recombination, is a basic determinant of species position on both spatial and successional gradients. Fourth, patches of different successional environments are continually changing size, position, and geographic relationship, depending on the disturbance regime. This presents a complex, dynamic pattern of selection pressures in the landscape that allows for the assortment of species into different successional positions. Successional gradients and the evolutionary and functional responses of populations on them are part of a dynamic, regional process rather than a single site pattern.