Founder effects and silvereyes

Abstract

Patterns of variation in nature have played a large role in the development of explanations for biological richness at the species level. One such influential pattern has been the morphological distinctiveness of small populations on islands at the periphery of a large continental land mass (1). If the island differs from the mainland in habitat or composition of the biological community, the morphological differences often can be explained in terms of adaptation by natural selection (2). But, if the environments are more or less the same, then an explanation has to be sought elsewhere. Fifty years ago, Ernst Mayr (3) suggested that the key to island evolution lies in the circumstances and immediate consequences of colonization. The model he proposed, called the ‘‘founder effects model,’’ postulated major changes in the genetic constitution of a newly established population that were set in motion by the reduced genetic variation carried by the few colonizing individuals in the founding event (4).