Bayliss, S. L. J., C. P. terHorst, and J. A. Lau. 2017. Testing genotypic variation of an invasive
plant species in response to soil disturbance and herbivory. Oecologia 183: 1135-1141. PDF
Herbivores, competitors, and predators can inhibit biological invasions (“biotic resistance” sensu Elton
1959), while disturbance typically promotes biological invasions. Although biotic resistance and disturbance are often considered separately in the invasion literature, these
two forces may be linked. One mechanism by which disturbance may facilitate biological invasions is by decreasing the effectiveness of biotic resistance. The effects of both disturbance and biotic resistance may vary across invading genotypes, and genetic variation in the invasive propagule
pool may increase the likelihood that some genotypes can overcome biotic resistance or take greater advantage of disturbance. We conducted an experimental field trial in which
we manipulated soil disturbance (thatch removal and loosening soil) and the presence of insect herbivores and examined their effects on the invasion success of 44 Medicago
polymorpha genotypes. As expected, insecticide reduced leaf damage and increased Medicago fecundity, suggesting that insect herbivores in this system provide some bioticr esistance. Soil disturbance increased Medicago fecundity, but did not alter the effectiveness of biotic resistance by
insect herbivores. We found significant genetic variation in Medicago in response to disturbance, but not in response to insect herbivores. These results suggest that the ability of Medicago to invade particular habitats depends on the amount of insect herbivory, the history of disturbance in the
habitat, and how the specific genotypes in the invader pool respond to these factors.
Keywords: Biological invasion · Genotype-by-environment interaction · Genetic variation · Herbivory · Tolerance
