Year of Award

2015

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Wildlife Biology

Department or School/College

College of Forestry and Conservation

Committee Chair

Thomas E. Martin

Commitee Members

Ragan M. Callaway, Mark Hebblewhite, John L. Maron, Douglas J. Emlen

Publisher

University of Montana

Abstract

Vegetation is the habitat that underlies animal distributions. Yet mechanisms by which dynamic changes in vegetation affect animal fitness, distributions, and communities remain unclear. For example, animal richness and species composition often change with decreased forest structural complexity associated with anthropogenic disturbance, but differences in latitude and vegetation effects on reproductive success may influence species responses to vegetation changes. My global meta-analysis of logging effects on bird communities revealed substantial species loss in tropical but not temperate forests. This suggests tropical birds exhibit greater habitat specialization than their temperate relatives.

My meta-analysis also suggested that changes in reproductive success can influence how animals distribute themselves in response to vegetation change. I examined this hypothesis with an in-depth observational study and landscape-scale experiment. Habitat use and nest predation rates were examined for 16 bird species that breeding along a deciduous to coniferous vegetation gradient and with experimental conifer removal from aspen stands. For most bird species, decreasing abundance was associated with increasing predation risk along both natural and experimentally modified vegetation gradients. This landscape-scale approach strongly supports the idea that vegetation-mediated effects of predation risk are associated with animal distributions and species turnover.

While direct predation mortality clearly has effects on animal population dynamics, the risk of predation alone may have equally large effects on reproduction and, ultimately, fitness. Yet the severity and generality of such demographic ‘costs of fear’ is unknown across species. I tested phenotypic responses to risk and associated demographic costs for 10 songbird species breeding along natural nest predation gradients and by experimentally increasing risk for four species. Parents decreased offspring development periods, reducing time-dependent nest mortality with natural and experimental increases in risk. Reproductive output from nests in the absence of direct predation generally declined along risk gradients, but the severity of this cost varied across species. Ultimately, demographic costs of fear reduced fitness across bird species, but not as strongly as direct predation mortality. These landscape and experimental tests suggest that vegetation affects the perceived risk of predation, and thereby strongly influences avian behaviors, fitness, distributions, and community assembly.

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© Copyright 2015 Joseph Anthony LaManna