title: Testing genotypic variation of an invasive plant species in response to soil disturbance and herbivory.
abstract: 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 biotic resistance. 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.
authors.affiliation: Biology Department, California State University, Northridge, Chaparral Hall 5301, 18111 Nordhoff Street, Northridge, CA, 91330-8238, USA. shannonljbay@gmail.com.
authors.forename: Shannon L J
authors.initials: SL
authors.lastname: Bayliss
authors.affiliation: Biology Department, California State University, Northridge, Chaparral Hall 5301, 18111 Nordhoff Street, Northridge, CA, 91330-8238, USA.|W.K. Kellogg Biological Station, Michigan State University, East Lansing, MI, USA.
authors.forename: Casey P
authors.initials: CP
authors.lastname: terHorst
authors.affiliation: W.K. Kellogg Biological Station, Michigan State University, East Lansing, MI, USA.|Department of Plant Biology, Michigan State University, East Lansing, MI, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Lau
mesh_terms: D000818:Animals; D017753:Ecosystem; D060434:Herbivory; D058865:Introduced Species; D010944:Plants; D012987:Soil
chemical_list: D012987:Soil
keywords: Biological invasion; Genetic variation; Genotype-by-environment interaction; Herbivory; Tolerance