Print PageThe Gopher Tortoise (Gopherus polyphemus) is federally threatened in the western portion of its range and under review for listing range-wide. Although primarily associated with sandhill, Gopher Tortoises occupy many habitats, some of which may be ecologically suboptimal. In peninsular Florida, pine (Pinus spp.) flatwoods and scrub dominate the uplands, and a substantial portion of extant tortoise populations may occupy these habitats, although few data are available to assess their status. In 2009, we used line transect distance sampling to determine Gopher Tortoise burrow densities, and assessed vegetation cover, in scrub, flatwoods and pine plantations on flatwoods soils, at Avon Park Air Force Range (APAFR) in south-central Florida.
Results/Conclusions
Despite low cover by food plants, the density of active burrows was significantly higher in scrub (0.54/ha) habitat with dry, friable soils, than in more mesic flatwoods/plantations (0.21/ha), where food was abundant but burrows were patchily distributed and often flooded. These densities were comparable to similar habitats at other Florida sites, but generally lower than in sandhill. Ratios of active, possibly active and collapsed burrows in scrub and flatwoods/plantations suggest a higher tortoise-to-burrow ratio in scrub, and frequent burrow abandonment, whereas tortoises in flatwoods/plantations appear to switch (and share) burrows frequently, but rarely abandon them altogether. Tortoises in scrub may abandon burrows when food resources become depleted, whereas burrow sharing in flatwoods/plantations may reflect a limitation on appropriate burrow conditions, perhaps due to poorly drained soils. We suggest that scrub and flatwoods/plantations constitute sub-optimal habitats. Nonetheless, given their large spatial extent in Florida, these habitats may support large numbers of tortoises at low densities. Our burrow survey provides an important initial step toward understanding Gopher Tortoise ecology in these poorly studied habitats, and suggests several hypotheses. First, low quality and quantity of forage in scrub may reduce the number of tortoises the habitat can support, and could influence demography through reduced clutch sizes and/or growth rates, with the latter leading to later age at first reproduction. Second, although food is abundant in flatwoods, flooding of mesic sites could reduce nest success. Population persistence in these suboptimal habitats may depend on complex source-sink dynamics or landscape supplementation, with tortoises taking advantage of critical resources in adjacent patches to meet their needs at different life history stages. We are seeking to address these intriguing possibilities through radiotelemetry of adults and intensive monitoring of populations in scrub and flatwoods habitats at APAFR.
