ANALYSIS OF ADAPTATION IN HETEROGENEOUS LANDSCAPES - IMPLICATIONS FOR THE EVOLUTION OF FUNDAMENTAL NICHES

The fundamental niche is a description of the range of environmental conditions in which the mean fitness of a population exceeds or equals unity, and outside of which its mean fitness is less than one. The fundamental niche is a mean phenotype of a population, a trait that can evolve by natural selection. In the analysis of the evolution of adaptations by natural selection one must specify the range of environments within which the relative fitnesses of alternative phenotypes are compared. Population dynamics automatically biases the environments experienced by an evolutionary lineage, simply because more individuals tend to be found within the fundamental niche than outside it (unless the population as a whole is going extinct). We argue that this basic asymmetry biases adaptive evolution toward further improvement to conditions inside the fundamental niche, even at the expense of fitness outside it. This suggests that natural selection may act principally as a conservative force on fundamental niches. We place the particular problem of the evolution of fundamental niches into the general framework of specifying the spatiotemporal scale for the analysis of adaptation in heterogeneous environments and introduce the notion of a 'phylogenetic envelope', a heuristic representation of this scaling. Because all of microevolution necessarily occurs within the constraint of the evolutionary dynamics of the fundamental niche, we conclude that understanding such dynamics should be of central concern to evolutionary ecologists.