Majority rule: adaptation and the long-term dynamics of species

Abstract

Where do species that become important players in ecosystems evolve? This simple yet crucial question must be answered if we want to understand how the biosphere is rejuvenated following a crisis. We cannot simply assume that the environments in which we find fossil remains of a given species, or living populations of a species, are the environments in which that species evolved. Take the most obvious example: Fossil human skeletons have been unearthed by the hundreds in North America, but all available evidence points to a human origin in Africa. We can often identify the general geographic origins of species and clades thanks to fossil occurrences and the application of phylogenetic techniques; but can we do likewise for more ecological aspects of the environment? Advances in population biology and in paleobiology now permit us to outline a hypothesis of the circumstances most favorable to the evolution of abundant, widespread, or ecologically powerful species, those with adaptations that are selectively advantageous across many environments, and large short-term and long-term effects in ecosystems. We can rephrase the problem and the question. Of the very large number of populations of a species inhabiting Earth at any given time, not all will contribute to the population composition of the species in the future. How does the environment in which a population is embedded affect the contribution that it will make over evolutionary time? The importance of this issue is underscored by the finding that the type and expression of selective regime varies greatly from place to place and over time within most species (Thompson 1994, 1998, 1999a,b; Benkman et al. 2001, 2003; Thompson and Cunningham 2002; Forde et al. 2004). Some populations of pollinating moths and figwasps, for instance, may have a mutualistic relationship with their …