Date of Award

8-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Wildlife and Fisheries Biology

Advisor

Baldwin,, Robert F

Committee Member

Brown , Bryan L

Committee Member

Scott , Mark C

Committee Member

Childress , Michael J

Committee Member

Hains , John J

Abstract

Human-induced disturbances can result in persistent influences on ecosystems, including habitat loss and biogeographical changes. Global amphibian decline, a consequence of habitat degradation, is among prime conservation concerns. To better understand causes of the amphibian crisis, investigations a multiple levels of biological organization - behavior, communities, and landscapes - is imperative. I investigated the responses of stream-associated Plethdontid salamanders of the Blue Ridge and Piedmont of the Southeastern US to historical and current land uses in the riparian zone and watershed to determine, (1) change in the community structure and mechanisms driving the change and uses operating at different spatial-temporal scales; (2) competition between two sympatric species with different body sizes, natural histories, and differential sensitivity for habitat alterations (black-bellied and northern dusky salamanders) in the context of riparian land uses.
I surveyed low-order streams for salamanders, estimated 15 habitat variables and current and historical land-cover at riparian and watershed scale for each sampling site. Forested streams were more diverse than non-forested streams. Two assemblages were evident: disturbance avoiders (forest-dependent, large-bodied, disturbance-sensitive species) and disturbance tolerators (cosmopolitan, small-bodied, disturbance-resistant species); each assemblage composed of 80% and 20% of the regional species pool, respectively. Riparian zone characteristics (canopy cover, canopy height, leaf-litter cover) and stream geomorphology (bank complexity, stream substrate heterogeneity, sedimentation) were dramatically altered by land uses, rendering streams unsuitable for most salamanders. Historical land uses at both riparian- and watershed-scale influenced current populations and community structure of salamanders. Piedmont protected areas with crop-farming legacies were the most species-deprived since intensive agriculture can lead to lasting effects including soil erosion, sedimentation, increased discharge, and destabilization of stream banks. My experiment on competition revealed marked differences in microhabitat associations of focal species across riparian land uses. Black-bellied salamanders competitively dominated the use of stream channel over northern dusky salamanders in forested and agricultural streams. Northern dusky salamanders competitively displaced black-bellied salamanders from stream banks in urban streams. Riparian anthropogenic disturbances negatively affected the large-bodied habitat specialists and favored small-bodied habitat generalists.
Terrestrial anthropogenic disturbances can modify stream habitats and, result in the exclusion of disturbance-sensitive species, ultimately leading to biotic homogenization. Conservation of stream salamander community should be strengthened with protection and restoration of riparian forests and degraded stream habitats; land-use regulations at the watershed scale; establishment of connectivity among riparian forests; and introduction of Best Management Practices for farmlands and timberlands.

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