Survival, demography, and growth of gopher tortoises (Gopherus polyphemus) from three study sites with different management histories

Abstract

The Journal of Wildlife Management 78(7):1151–1160; 2014; DOI: 10.1002/jwmg.773 Research Article Survival, Demography, and Growth of Gopher Tortoises (Gopherus polyphemus) from Three Study Sites with Different Management Histories TRACEY D. TUBERVILLE, 1 University of Georgia’s Savannah River Ecology Lab, Drawer E, Aiken, SC 29802, USA BRIAN D. TODD, Department of Wildlife, Fish, and Conservation Biology, University of California, Davis, One Shields Ave, Davis, CA 95616, USA SHARON M. HERMANN, Department of Biological Sciences, Auburn University, Auburn, AL 36849, USA WILLIAM K. MICHENER, University Libraries, 1312 Basehart SE, Albuquerque, NM 87106, USA CRAIG GUYER, Department of Biological Sciences, Auburn University, Auburn, AL 36849, USA ABSTRACT Recovery or sustainable management of wildlife populations often entails management of habitat on which they depend. In this regard, turtles pose unique conservation challenges because of their life histories. The combination of late maturity, low survival when young, and dependence on high adult survival suggests they may be slow to respond demographically to conventional habitat management. Thus, long- term studies are necessary to understand population dynamics and recovery potential in these species. We used 5–11 years of mark-recapture data from 3 populations to evaluate survivorship, demography, and somatic growth of gopher tortoises (Gopherus polyphemus). Green Grove and Wade Tract (southwest GA) are ecological reserves with a history of land management compatible with tortoises. In contrast, Conecuh National Forest (south-central AL) is a closed-canopy pine plantation with prior intensive site preparation but where management intervention improved habitat for tortoises during the study. Apparent survival was high for mature tortoises (87–98%) compared to immature tortoises (70–82%). Adults comprised 57–79% of individuals captured, with Green Grove and Wade Tract populations dominated by larger individuals but Conecuh having a more uniform size distribution. The largest adults captured at Conecuh (297 mm maximum carapace length [CL]) were smaller than the largest adults from Green Grove (337 mm CL) or Wade Tract (341 mm CL), although characteristic growth constants from von Bertalanffy models were similar among sites. We suggest these results indicate a recovering population at Conecuh, where habitat conditions for gopher tortoises have improved despite a legacy of intense predation by humans and reduced habitat quality at the inception of this national forest. Further, we recommend using a combination of short- term and long-term monitoring metrics to assess population recovery in such long-lived species. O 2014 The Wildlife Society. KEY WORDS demography, gopher tortoise, Gopherus polyphemus, growth, habitat management, population recovery, survivorship. Turtles are among the most imperiled vertebrate group globally, with nearly 66% classified as “vulnerable to extinction” or worse (International Union for the Conserva- tion of Nature [IUCN] 2012). Turtles offer a unique set of conservation challenges due to their slow life history strategies. The combination of high hatchling and early juvenile mortality, high adult survivorship and longevity, delayed sexual maturity, and low reproductive output (Gibbons 1987, Iverson 1991) makes them vulnerable to demographic perturbations (Brooks et al. 1991, Congdon Received: 29 May 2013; Accepted: 26 June 2014 Published: 26 August 2014 E-mail: tubervil@uga.edu Tuberville et al. Survival, Demography, and Growth in Tortoises et al. 1993, but see Fordham et al. 2007). Likewise, these traits also limit the ability of turtle populations to recover even after threats have abated (Bailey and Guyer 1998, Hall et al. 1999, Tucker et al. 2001, Troe¨ng and Rankin 2005). The gopher tortoise (Gopherus polyphemus) is restricted to the Coastal Plain physiographic province in the southeastern United States and was historically associated with the longleaf pine (Pinus palustris) ecosystem. Less than 3% of the original longleaf pine ecosystem remains, mostly as small, isolated fragments (Ware et al. 1993, Means 2006). Because of this habitat loss, many of the more than 200 associated vertebrate species, including the gopher tortoise, have also experienced dramatic declines (Means 2006). In 1987, the western population of the gopher tortoise was federally listed as threatened, and in 2011, the United States Fish and