Data from: Genetic variation in invasive species response to direct and indirect species interactions

Biotic resistance to invasion arises from strong species interactions that
decrease the fitness and population growth rates of potential invaders.
Strong, direct interactions such as predation and competition are
typically thought to drive biotic resistance, but in diverse communities,
indirect interactions among species may also affect biotic resistance.
Further, genetic variation in traits of the invading species that affect
species interactions may allow some genotypes to overcome biotic
resistance. We investigated the direct and indirect effects of a native
legume (Acmispon wrangelianus) and insect herbivores on the fitness of
different genotypes of an invasive legume (Medicago polymorpha) in a
California grassland. Insect herbivores decreased Medicago fitness, but
only in the presence of Acmispon, suggesting that indirect interactions
mediated through insects and Acmispon are important for deterring Medicago
invasion. Some Medicago genotypes were less affected by interactions with
other species, however. This genetic variance suggests that while biotic
resistance reduced the reproductive success of most genotypes, a few
genotypes were able to overcome these complex interactions. However,
Medicago invasion was unsuccessful in all treatments at several of our
sites, suggesting that factors beyond those manipulated here also play a
key role at many sites. At sites where biotic resistance is important,
spatial and temporal variation in community composition and the genetic
composition of the invasion pool may explain the invasion success of
Medicago into this community.