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1 September 2012 Gopher Tortoise Hatchling Survival: Field Study and Meta-Analysis
Carolina Perez-Heydrich, Katharine Jackson, Lori D Wendland, Mary B Brown
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Abstract

The Gopher Tortoise (Gopherus polyphemus) is a keystone species whose burrowing activities are of critical importance for upland ecosystems. Perhaps no age class is as enigmatic or vulnerable as hatchlings, and understanding the survival dynamics of hatchlings is critical for the parameterization of population viability models that will help guide adaptive management of this threatened species. Meta-analysis is a particularly useful technique for integrating results of published studies that provide different estimates of a single parameter of interest. A summary value from multiple studies could therefore provide a more representative estimate of a vital rate across heterogeneous study populations. We estimated hatchling survivorship from a natural population in North Florida using hatchling cohorts from a 3-yr telemetry study. To provide continuous estimates of survival through time, we fit weekly telemetry data to Weibull survival curves. We then incorporated the least biased estimate of hatchling survival from the field study into a meta-analysis, which included values from four other published studies, to generate a single summary estimate of hatchling survivorship through the first year of life. With the field study, we found significant differences in survival among years (P = 0.0073), release months (P = 0.0022), and hatching months (P = 0.0053). Hazard ratios (HR) indicated that hatchlings released in November were approximately 70% less likely to die within the first year of life than were hatchlings released in September (HRNov = 0.285, 95% confidence interval [CI] = 0.148–0.549). After incorporating our field estimates of survival with published estimates from other studies, we estimated the overall annual survival rate of hatchlings at 0.128 (CI = 0.040–0.340). Many factors, such as habitat and predator composition, may contribute to heterogeneities in hatchling survival among tortoise populations. Therefore, we suggest that the use of a composite estimate rather than a single estimate would provide for a more representative and less biased description of hatchling survival. We recommend the use of this summary estimate of hatchling survival for future parameterization of population projection models.

Carolina Perez-Heydrich, Katharine Jackson, Lori D Wendland, and Mary B Brown "Gopher Tortoise Hatchling Survival: Field Study and Meta-Analysis," Herpetologica 68(3), 334-344, (1 September 2012). https://doi.org/10.1655/HERPETOLOGICA-D-11-00046.1
Accepted: 1 May 2012; Published: 1 September 2012
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