Year of Award

2017

Document Type

Thesis - Campus Access Only

Degree Type

Master of Science (MS)

Degree Name

Organismal Biology, Ecology, and Evolution

Department or School/College

Division of Biological Sciences

Committee Chair

John L. Maron

Commitee Members

Ragan M. Callaway, Dean E. Pearson, Tom E. Martin, Angela D. Luis

Keywords

context-dependence, demography, environmental gradients, productivity, recruitment, seed predation

Publisher

University of Montana

Subject Categories

Ecology and Evolutionary Biology | Population Biology

Abstract

Plants frequently face attack by consumers resulting in seed loss. However, our ability to predict whether a decrease in seeds results in parallel changes in future recruitment or plant abundance remains poor. Progress in this area requires understanding:1) how spatial variation in environmental conditions influence recruitment and other demographic rates, 2) how the magnitude of seed loss varies relative to recruitment rates, and 3) the relative importance of intraspecific competition in simultaneously influencing recruitment. I experimentally assessed how post-dispersal seed predation by deer mice (Peromyscus maniculatus) influenced recruitment of the native perennial forb, Gaillardia aristata. To explore whether seed limitation and the population-level consequences of seed predation varied predictably based on environmental conditions, I performed seed addition experiments, allowing rodent access or not, across sites occurring over strong gradients soil attributes and plant community productivity. I also quantified whether other components of Gaillardia demography varied predictably across these environmental gradients. Finally, at a subset of highly productive sites, I experimentally removed the community dominant, rough fescue (Festuca campestris), to compare reductions in recruitment from competition to those of post-dispersal seed predation. Across two replicate years, post-dispersal seed predation strongly reduced Gaillardia recruitment. Reductions in recruitment from mice were greater at sites with lower productivity and less soil resources (where recruitment was higher in the absence of rodents) and decreased toward the opposite ends of the gradients. Growth and fecundity varied in ways that could buffer Gaillardia populations from strong effects of seed predation, but survival varied in a way that may intensify them. Surprisingly, competitive interactions with surrounding bunchgrasses had little impact on Gaillardia recruitment, especially compared to the effects of rodent seed predation. Together, my results show that post-dispersal seed predation can strongly limit future recruitment of Gaillardia, and that the magnitude of these effects can be mediated by variation in underlying environmental conditions that affect levels of plant recruitment as well as survival, growth, and fecundity.

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© Copyright 2017 Ryan James Hegstad