Consequences of hybridization during invasion on establishment success

Abstract

Initial colonization by non-native species sometimes occurs in regions already occupied by closely related species, and subsequent hybridization is often inevitable. However, there are several different ways that such hybridization might affect the successful establishment of the non-native species, but many of these remain insufficiently explored. Although there is growing evidence in support of improved local adaptation by genetic rescue, we demonstrate here another way that closely related species can facilitate invasions in which hybridization assists the invading species to overcome Allee effects arising from mate-finding failure. We explore this phenomenon using a simple mathematical model of two closely related diploid insect species, native and non-native, exhibiting differences in mate searching efficacy, relative strength of competition, and mate preference. We find that when the carrying capacity in the invading species is higher than in the native species, invasion success is facilitated. Invasion is also facilitated under parameterization for high hybrid fitness and severe competition between natives and hybrids. In light of these results, we discuss general patterns of how invasion success is affected by the manner in which native, non-native, and hybrids interact with each other and note situations where such conditions might occur in nature.