Title page for ETD etd-05042012-104133


Type of Document Master's Thesis
Author Legleu, Christina
URN etd-05042012-104133
Title Modeling Gopher Tortoise (Gopherus polyphemus) Habitat in a Fire-Dependent Ecosystem in North Florida
Degree Master of Science (M.S.)
Department Renewable Natural Resources
Advisory Committee
Advisor Name Title
Nyman, John A Committee Chair
Austin, Christopher Committee Member
Kaller, Mike Committee Member
Stouffer, Phil Committee Member
Keywords
  • gopher tortoise
  • habitat
  • fire
  • model
  • longleaf pine
Date of Defense 2012-03-08
Availability unrestricted
Abstract
Gopher tortoise (Gopherus polyphemus) populations have declined with longleaf pine (Pinus palustris) ecosystems across their historic range. The influence of gopher tortoise burrows on co-inhabiting plants and animals necessitates an understanding of how landscape features and management practices influence gopher tortoise presence, absence, and abandonment. In this study, na´ve gopher tortoise burrow encounter rates from a line transect distance sampling (LTDS) pilot study were used for two methods of modeling gopher tortoise habitat.

In Chapter 1, na´ve encounter rates were tested for a linear correlation to a HSI model created from three ranked geographic information system (GIS) landscape variables. Initial results showed a positive linear correlation (all P < 0.0001, 0.55 < r< to 0.70) but a second test using only transects with observed burrows resulted in the loss of all correlations (all P > 0.05, r values ranged from 0.17 to 0.42). However, logistic regression analysis revealed the HSI model was able to predict burrow presence along transects (P = 0.0003).

In Chapter 2, microhabitat variables and five GIS landscape variables were reduced into seven correlated principal components (PCs). According to a generalized linear (logit) model three PCs were significantly associated to active and abandoned borrows. Active burrows were positively associated to: 1) sandhill habitats, longleaf pine canopy, Lakeland soils, high elevations, xeric oak midstory, and wiregrass (Aristida beyrichiana) presence (overall P = 0.003; active P = 0.008); and 2) grassland habitats, little to no canopy, and increased herbaceous ground cover (overall P = 0.0042; active P = 0.0052). Active burrows were negatively associated to mesic flatwoods, Scranton soils, mixed pine canopy, high basal areas, and increased percent tree canopy (overall P = 0.003; Active P = 0.008). Abandoned burrows were positively associated to xeric hammocks, xeric hardwood canopy, mesic hardwoods midstory, increased canopy cover, increased litter ground cover, and increased mean years between burns (overall P = 0.0448; abandoned P = 0.0137). The relationship between fire suppression and burrow abandonment is widely accepted but poorly documented, and the poor resolution of this fire layer accentuates the importance of this detected relationship.

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