Dissertation/Thesis Abstract

Modeling occurrence of the green salamander, aneides aeneus, in the blue ridge escarpment
by Hardman, Rebecca Hale, M.S., Western Carolina University, 2014, 42; 1570497
Abstract (Summary)

Amphibian species have experienced global declines since the 1970s and plethodontid salamanders are no exception. The green salamander, Aneides aeneus, is a plethodontid salamander that has experienced declines throughout its range in the Blue Ridge Escarpment.

Species distribution models are algorithms that predict occurrences of a species across a landscape and can be used to determine conservation priority areas. However, there are commonly only presence locations without corresponding absence locations available to a researcher. These presence-only datasets can present a challenge when trying to depict reliable distributions for a species of concern. Maximum Entropy (MaxEnt) is an algorithm empirically tested to model species distributions given presence-only datatsets.

I used landscape-level species distribution models including MaxEnt and logistic regression to model the occurrence of green salamanders across the Blue Ridge Escarpment of North Carolina. These models were used to assess particular features associated with A. aeneus presence as well used to search for new localities.

MaxEnt models outperformed logistic regressions for all methods of evaluation. MaxEnt models had fairly low omission (false negative) and commission (false positive) rates whereas my logistic regression had extremely high error rates for both. "Area Under the Receiver Operator Curve" evaluation scores were excellent (0.96) and good (0.81) for the top Maxent model and logistic regression, respectively.

Aneides aeneus is known to be associated with habitat that includes rock outcroppings with thin, deep crevices. My models indicated that forested areas, intermediate elevations, and shallow soils of particular types are desirable landscape features for A. aeneus. Soil was the most important variable in all models, accounting for almost half of the variation in MaxEnt models. Elevation accounted for most of the remaining variation. Percent canopy cover accounted for 4-6.5% of the variation in Maxent models. While these models did not specifically predict presence of outcrops, they were extremely helpful in identifying habitat with conditions supportive for A. aeneus if a rock outcrop was present. With the help of these models I discovered one previously unknown locality for A. aeneus and am confident addition locations can be found.

Indexing (document details)
Advisor: Pechmann, Joseph H K
Commitee: Davis, Ronald, Martin, Thomas H.
School: Western Carolina University
Department: Biology
School Location: United States -- North Carolina
Source: MAI 54/02M(E), Masters Abstracts International
Subjects: Conservation
Keywords: Aneides aeneus, Green salamander, MaxEnt, Plethodontidae, Species distribution model
Publication Number: 1570497
ISBN: 978-1-321-39117-6
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