Genetic Variation in Invasive Species

The particular genotypes that invade a habitat may determine whether a species successfully invades that habitat. We are interested in which abiotic and biotic factors affect invasion success and whether certain genotypes are able to overcome those factors.

Biotic resistance to invasion arises from strong species interactions that decrease the fitness of potential invaders. However, the efficacy of biotic resistance may depend on the complexity of interactions in the native community and the ability of species to overcome biotic resistance. We are interested in biotic resistance resulting from the direct and indirect effects of a competitor (Lotus wrangelianus) and insect herbivores (primarily Egyptian alfalfa weevils) to invasion by the non-native legume (Medicago polymorpha). Insect herbivores tend to decrease Medicago fitness, but only in the presence of Lotus, suggesting that indirect effects mediated through herbivores and competitors increase biotic resistance. However, some Medicago genotypes were less affected by biotic resistance; insect herbivores strongly reduced the fitness of Medicago genotypes from the native range, but had less effect on genotypes from the invasive range. Thus, biotic resistance, primarily resulting from indirect effects, reduced the reproductive success of most genotypes, but a few genotypes were able to overcome biotic resistance and may explain the successful invasion of Medicago into this community.