GOPHER TORTOISE GOPHERUS POLYPHEMUS) DENSITIES AND HABITAT SUITABILITY ACROSS A XERIC-MESIC GRADIENT IN PENINSULAR FLORIDA, USA

Gopher Tortoise (Gopherus polyphemus) is a burrowing, keystone species of the southeastern USA. Factors influencing habitat suitability for this declining species in the southern portion of its range are unclear, due to its broad habitat associations and lack of detailed demographic data. We used Line-transect Distance Sampling of burrows to determine densities and estimate age-class structure of Gopher Tortoises across a gradient of xeric to mesic habitats on Avon Park Air Force Range (APAFR) in south-central Florida. We also examined the influence of soil characteristics on burrow encounter rates. Tortoise densities were highest in Florida scrub (0.95 adult and subadult tortoises/ha), intermediate in pine flatwoods (0.73) and pine plantations (0.44), and lowest in prairies (0.18). Despite persistent burrow flooding that hindered precise density estimation for mesic habitats, we estimated that APAFR harbors a regionally significant population of 7,899-11,109 adult and subadult tortoises. We encountered more burrows per km in soils with intermediate available water capacity (r(2) = 0.45, df = 2,11, P = 0.036,), suggesting a tradeoff in habitat suitability between wetter soils that may support the most forage and drier soils that may be most appropriate for burrowing and nesting. Burrow size-class distributions were skewed towards adult sizes, particularly in pine and prairie communities. Variation in tortoise densities and age-class structure across this xeric-mesic gradient implies differences in recruitment and survival arising from corresponding variation in habitat quality. Our study provides useful reference densities for species management and new insights regarding Gopher Tortoise use of poorly drained soils and non-forest habitats.