1. Pollen-mediated gene flow from ecological core populations may hamper the ability of populations to invade new, closely adjacent habitats. The potential for the invasion of a new habitat is enhanced when selection against immigrants is augmented by the elevation of self-fertilization. This shift imparts a measure of reproductive isolation to the invader.
2. Whereas genetically mediated changes in selfing often accompany niche shifts in plants, the elevation of self-fertilization by plastic responses to novel, stressful, environments has not been explored. Here I will show that invaders of novel habitats may have elevated levels of self-fertility mediated by alterations in floral form and self-compatibility.
3. Heightened selfing facilitates the evolution of local adaptation by increasing the additive genetic variance for tolerance to the new habitat. Heightened selfing also facilitates local adaptation by increasing reproductive assurance.
4. Elevated levels of selfing based on developmental responses are immediate, as opposed to that obtained by multigenerational selection.
5. Synthesis. The likelihood of a niche shift will be substantially enhanced if the invader is protected from the swamping effect of gene flow from a nearby core population. This protection may be afforded by an environment-induced elevation of self-fertility. The likelihood of a niche shift also is enhanced by an increase in reproductive assurance which may be vital to the survival of an invading population whose reproductive success is density-dependent.