The magnitude of niche shifts associated with ecological speciation and the factors that regulate the process are poorly understood. I propose that ecological transitions most often involve the invasion of habitats most accessible through seed dispersion and by relatively small genetic changes. A significant seed rain is required for the recruitment of chance variants that are somewhat adapted to the novel conditions, as well as for the expansion of the genetic repertoire necessary for the evolution of a well-adapted entity. The probability of exploiting a new niche is an inverse function of the amount of genetic change that is required. Genes with large effect facilitate the change. There is considerable evidence that substantial habitat and pollinator niche shifts may occur with relatively few gene changes. There is speculation that populations may establish in new habitats through adaptive developmental and physiological changes induced by the environment, and then undergo genetic changes that stabilize the new phenotypes. Hybridization provides an unusual opportunity for major ecological change over a relatively short time span.
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