Population Structure and Burrow Placement of Gopherus polyphemus in a Small, Declining Southeast Florida Conservation Area

Gopherus polyphemus has been declining throughout its range since the 1800s primarily due to urbanization, which often leads to the creation of island habitats. This confines populations and eliminates natural management by wildfires resulting in degraded island habitats. To maximize conservation efforts in rapidly developing regions it is critically important to investigate not only the natural ecology of native species, but also how they are doing in habitats set aside for them. We studied a gopher tortoise population to determine its sustainability and burrow placement across different soil and vegetation types in a conservation area on the Florida Atlantic University campus in Boca Raton, Florida. We conducted complete burrow surveys using belt transects, directly captured tortoises, and performed vegetation and soil analyses through aerial photos and United States Geological Survey data, respectively. The sustainability of the population was based directly on age structure, gained from carapace length measurements, and indirectly on ratios of active to abandoned burrow categories. Tortoises burrowed densely in areas of low vegetation and completely avoided areas with closed canopies, which comprised about 15% of the habitat. Soil types had a significant correlation to the spatial distribution of burrows. We found a high ratio of active to abandoned burrows, which could indicate an active and healthy population; however, age structure data compiled from captured tortoises revealed a lack of sub-adults, suggesting an unsustainable population. We concluded that tortoise surveys which solely collect data on burrow numbers and activity level and not tortoise sizes may provide misleading results on the status of gopher tortoise populations in confined, degraded habitats. More direct population assessment methods such as tortoise captures or burrow measurements need to be used.