Factors Influencing Reproductive Output and Egg Size in a Southern Population of Gopher Tortoises

Abstract

Comparative life-history data are needed to develop effective conservation plans for Gopherus polyphemus (Gopher Tortoise), a threatened species that inhabits diverse ecosystems throughout its range. In 2010–2011, we measured and radiographed 27 female Gopher Tortoises occupying Florida scrub and mesic flatwoods habitats at Avon Park Air Force Range in south-central Florida. Counter to predictions of optimal egg size theory, both clutch size and mean egg width (measured via x-rays) increased significantly with body size. Furthermore, our data suggest the presence of a non-pelvic constraint on egg size in this species. Despite greater cover of grasses and forbs in flatwoods, clutch size, egg width, and female body condition were similar in flatwoods and scrub. Thus, the relatively low density of juvenile-sized burrows in flatwoods is not a result of low fecundity. Body condition tended to be higher in the wetter spring of 2010, although seasonal differences were not statistically significant. Clutch sizes at Avon Park Air Force Range (range = 4–9 eggs; overall mean = 5.8 ± 1.2) were comparable to other populations, but lower than reported for some peninsular Florida populations. Further research is needed to explain variation in reproductive output among individuals and populations in the southern part of the species' range.