title: Potential impacts of tolerance to herbivory on population dynamics of a monocarpic herb.
abstract: OBJECTIVE
  Mammalian herbivores, particularly white-tailed deer, can have a major impact on plant abundance and distribution. However, plants can tolerate herbivory by increasing seed production or seed quality. We used the monocarpic perennial Prenanthes roanensis to examine tolerance to mammalian herbivory through seed quality and modeled the effects of tolerance on population growth rate.
  
  
  METHODS
  We examined seed quality (proportion of viable seeds, seed mass, germination, and seedling size) on damaged and undamaged plants to determine the extent to which plants tolerate herbivory. We then varied seed quality parameters over a range of values in population models to compare population growth rates under "no-tolerance" conditions (herbivory, but no tolerance) to those under "tolerance" conditions.
  
  
  RESULTS
  In most populations, plants damaged by herbivores had a greater proportion of viable seeds per plant or a greater probability of seed germination. Incorporating observed tolerance into population models did not significantly increase population growth rate. However, at low germination rates, increased germination of seeds from damaged plants has the potential to significantly increase population growth rate.
  
  
  CONCLUSIONS
  Damaged plants can compensate for loss of reproductive heads by increasing seed viability and germination rates in the remaining seeds. This study is one of the first to demonstrate that tolerance through seed quality has the potential to affect population growth rate. Our results suggest that incorporating tolerance into population models may help elucidate mechanisms by which plant populations persist despite herbivory.
authors.affiliation: Department of Biology, University of Virginia, P. O. Box 400328, Charlottesville, Virginia 22904 USA mla2j@virginia.edu.
authors.forename: Melissa L
authors.initials: ML
authors.lastname: Aikens
authors.affiliation: Department of Biology, University of Virginia, P. O. Box 400328, Charlottesville, Virginia 22904 USA.
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Roach
mesh_terms: D000818:Animals; D019659:Asteraceae / Q000254:growth & development / Q000502:physiology*; D018525:Germination; D060434:Herbivory; D008018:Life Cycle Stages; D008954:Models, Biological; D011157:Population Dynamics; D012098:Reproduction; D036226:Seedlings / Q000254:growth & development / Q000502:physiology; D012639:Seeds / Q000254:growth & development / Q000502:physiology*
keywords: Asteraceae; Prenanthes roanensis; compensation; fecundity; germination; monocarp; population growth rate (λ); population variability; seed quality; seed viability; tolerance