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Seasonal Distribution and Home Ranges of Gopher Tortoises Gopherus polyphemus on a Barrier Island in Southwest Florida

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Date Issued:
2020-04-28
Abstract/Description:
The gopher tortoise (Gopherus polyphemus) resides in multiple habitats throughout the coastal plains ecosystem of southeastern United States. A thorough understanding of the spatial ecology across all habitats is needed to determine best management practices. In pine flatwoods, male gopher tortoises exhibit larger home ranges than females, but all adults generally maintain home ranges under one hectare (Eubanks et al., 2003). Recent studies indicate tortoises in scrub and mesic flatwoods habitats exhibit home ranges that can reach six hectares (Castellón et al., 2018). This study examines the home range and movement of 17 gopher tortoises in a coastal dune population in southwest Florida. We tracked 10 tortoises (6 females : 4 males) for 20 months from September 2013 through April 2015. Five radio tags failed after 10 months so those individuals could not be used for seasonal analyses. We also tracked an additional seven tortoises (4 females : 3 males) for 10 months from July 2016 through April 2017. We visited the sites one to two times per week, depending on weather conditions, to locate the tortoises. We then determined home range sizes by generating minimum convex polygons using convex hull geometry in QGIS. All animals were active year-round, and males had a larger mean home range than females (male = 0.8 ha, female = 0.28 ha) (F1,16=7.6, p=0.02) over the total study period. Female tortoises utilized only 25% (0.07 ha) of their total home range during the warmest three months of the year (July-September), but occupied 52% (0.36 ha) of their home range during the coolest three months (December-February). Males utilized 26% (0.2 ha) of their home range during the hottest and 26% (0.2 ha) during the coolest three-month periods. The home range did not vary with wet/dry season (t=0.005, p=1) and was not correlated with body size (F1,14=0.004, p=0.95, r2<0.01). Mean home range size measurements were similar to data recorded in pine upland habitats, and much lower than those from mesic flatwoods and scrub. The tortoises primarily utilized the coastal dune habitats, but also exhibited movements through the beach zone that included reaching the water. Movement patterns in this study illustrate the animals are active and seeking social interactions year-round. This could have implications for behavioral and genetic differences between populations when relocating gopher tortoises, could impact growth rates and adult sizes of tortoises, and influence mating and reproductive patterns.
Title: Seasonal Distribution and Home Ranges of Gopher Tortoises Gopherus polyphemus on a Barrier Island in Southwest Florida.
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Name(s): Beyer, Kristin, Author
Type of Resource: text
Genre: Thesis
Issuance: monographic
Date Issued: 2020-04-28
Extent: 66 pgs.
Language(s): English
eng
Abstract/Description: The gopher tortoise (Gopherus polyphemus) resides in multiple habitats throughout the coastal plains ecosystem of southeastern United States. A thorough understanding of the spatial ecology across all habitats is needed to determine best management practices. In pine flatwoods, male gopher tortoises exhibit larger home ranges than females, but all adults generally maintain home ranges under one hectare (Eubanks et al., 2003). Recent studies indicate tortoises in scrub and mesic flatwoods habitats exhibit home ranges that can reach six hectares (Castellón et al., 2018). This study examines the home range and movement of 17 gopher tortoises in a coastal dune population in southwest Florida. We tracked 10 tortoises (6 females : 4 males) for 20 months from September 2013 through April 2015. Five radio tags failed after 10 months so those individuals could not be used for seasonal analyses. We also tracked an additional seven tortoises (4 females : 3 males) for 10 months from July 2016 through April 2017. We visited the sites one to two times per week, depending on weather conditions, to locate the tortoises. We then determined home range sizes by generating minimum convex polygons using convex hull geometry in QGIS. All animals were active year-round, and males had a larger mean home range than females (male = 0.8 ha, female = 0.28 ha) (F1,16=7.6, p=0.02) over the total study period. Female tortoises utilized only 25% (0.07 ha) of their total home range during the warmest three months of the year (July-September), but occupied 52% (0.36 ha) of their home range during the coolest three months (December-February). Males utilized 26% (0.2 ha) of their home range during the hottest and 26% (0.2 ha) during the coolest three-month periods. The home range did not vary with wet/dry season (t=0.005, p=1) and was not correlated with body size (F1,14=0.004, p=0.95, r2<0.01). Mean home range size measurements were similar to data recorded in pine upland habitats, and much lower than those from mesic flatwoods and scrub. The tortoises primarily utilized the coastal dune habitats, but also exhibited movements through the beach zone that included reaching the water. Movement patterns in this study illustrate the animals are active and seeking social interactions year-round. This could have implications for behavioral and genetic differences between populations when relocating gopher tortoises, could impact growth rates and adult sizes of tortoises, and influence mating and reproductive patterns.
Identifier: fgcu_ETD_0334 (IID)
Note(s): Degree Awarded: Master of Science
Department of Ecology & Environmental Studies
Committee Chair: Phil Allman, Ph. D.
Committee: Edwin Everham, Ph. D.; Brian Bovard, Ph. D.
Subject(s): Gopher tortoise
Home range (Animal geography)
Florida
Persistent Link to This Record: http://purl.flvc.org/fgcu/fd/fgcu_ETD_0334
Use and Reproduction: Creator(s) holds copyright.
Use and Reproduction: http://rightsstatements.org/vocab/InC/1.0/
Host Institution: FGCU