title: Tree seedling richness, but not neighborhood composition, influences insect herbivory in a temperate deciduous forest community.
abstract: Insect herbivores can serve as important regulators of plant dynamics, but their impacts in temperate forest understories have received minimal attention at local scales. Here, we test several related hypotheses about the influence of plant neighborhood composition on insect leaf damage in southwestern Pennsylvania, USA. Using data on seedlings and adult trees sampled at 36 sites over an approximately 900 ha area, we tested for the effects of total plant density, rarefied species richness (i.e., resource concentration and dietary-mixing hypotheses), conspecific density (i.e., Janzen-Connell hypothesis), and heterospecific density (i.e., herd-immunity hypothesis), on the proportion of leaf tissue removed from 290 seedlings of 20 species. We also tested for the effects of generic- and familial-level neighborhoods. Our results showed that the proportion of leaf tissue removed ranged from zero to just under 50% across individuals, but was generally quite low (<2%). Using linear mixed models, we found a significant negative relationship between insect damage and rarefied species richness, but no relationship with neighborhood density or composition. In addition, leaf damage had no significant effect on subsequent seedling growth or survival, likely due to the low levels of damage experienced by most individuals. Our results provide some support for the resource concentration hypothesis, but suggest a limited role for insect herbivores in driving local-scale seedling dynamics in temperate forest understories.
authors.affiliation: Department of Evolution, Ecology and Organismal Biology The Ohio State University 318 W. 12th Avenue Columbus Ohio 43210-1293.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Murphy
authors.affiliation: School of Forestry and Environmental Studies Yale University 195 Prospect Street New Haven Connecticut 06511.
authors.forename: Kaiyang
authors.initials: K
authors.lastname: Xu
authors.affiliation: School of Forestry and Environmental Studies Yale University 195 Prospect Street New Haven Connecticut 06511; Smithsonian Tropical Research Institute Box 0843-03092 Balboa Ancón Panama.
authors.forename: Liza S
authors.initials: LS
authors.lastname: Comita
keywords: Density dependence; Janzen–Connell; diversity; herd immunity; mixed model; resource concentration; seedling dynamics