Determining habitat preferences of the juvenile gopher tortoise (Gopherus polyphemus) using spatially modeled vegetation on a central Florida sandhill

Public and private conservation areas are becoming increasingly important to the continued survival of the gopher tortoise, making it imperative that land managers know the specific habitat requirements of juvenile gopher tortoises because recruitment is key to species persistence. Little is currently known about environmental factors that underlie hatchling and juvenile survival and recruitment in gopher tortoise populations. Because of the short duration and distance of juvenile tortoise foraging journeys, food availability, thermoregulatory conditions, and refugia near the burrow may considerably affect juvenile growth and survival. This two-year study of a central Florida sandhill examines the spatial relationship between juvenile gopher tortoise burrows and the surrounding habitat. Gopher tortoise burrow positions, activity, and width were recorded in four complete surveys of the 4-hectare study area. Coincident with three of the burrow surveys, vegetation and structural habitat characteristics, such as forb and canopy cover, were surveyed in a uniform grid design. Vegetation cover was reclassified using habitat suitability functions (HSFs) derived from qualitative literature values and combined into habitat suitability indices (HSIs) to model the relationships between habitat variables and the likelihood of juvenile gopher tortoise presence. Chi-squared tests and spatial point pattern analysis were used to validate and identify well-forming models. In general, the best performing HSI models for the juvenile gopher tortoise were those that incorporated all three gopher tortoise life requisites in a compensatory relationship (geometric mean): thermoregulation (total high canopy, bare ground, or litter), predation (oak mid-canopy), and food (forb or wiregrass). The models could be improved by using the observed relative abundance of juvenile burrows in each vegetation cover class to modify the HSFs. These methods will help identify habitat characteristics associated with active juvenile gopher tortoise burrows that can be used by public and private land managers to improve existing tortoise habitat and to identify high-quality habitat for future preserves