PS 22-40 - Population Viability Analysis of the Eastern Diamondback Rattlesnake

Abstract: The eastern diamondback rattlesnake (Crotalus adamanteus) is one of North America’s largest venomous snakes and as apex predators, they are a critical taxon within their ecosystems. Historically, eastern diamondbacks ranged across the coastal plains of the southeastern United States, however, reliance on a vanishing longleaf pine habitat and human persecution have caused their populations to decline markedly. Given this decline, our goal was to provide a starting point for further consideration of eastern diamondback rattlesnake vulnerability and enable general prioritization for filling demographic data gaps for the snake. To address this, we conducted a population viability analysis (PVA) to fill current knowledge gaps and allow managers to evaluate tradeoffs in options to conserve the species. We developed a baseline model of eastern diamondback population trends based on the best available natural history information and then developed a suite of population models under different reported estimates of key vital rates. Further, we conducted elasticity analyses of vital rates to evaluate which demographic parameters are most sensitive to uncertainty. Our model was least sensitive to initial population size and carrying capacity and moderately sensitive to all the fecundity measures (litter size, percent of females breeding each year, age at first breeding), although not nearly as sensitive as it was to mortality measures. The baseline model suggests that with suitable habitat the snake population could increase to some moderate level and persist with no likelihood of extinction. However, these patterns should be viewed with high caution, as they largely reflect the species’ demographic potential for increase, rather than capturing current patterns, particularly as site-specific information about eastern diamondback rattlesnake status, trends, and demographic rates are limited. As we varied vital rates within the range of existing data, most populations persisted with little to no chance of extinction. However, as juvenile mortality, breeding interval, and duration of juvenile mortality, the viral rates least supported by data, increased the population’s growth and final size decreased markedly and resulted in increased likelihood of extinction. In addition, at nearly any level of harvest, we saw decreases in growth rates and population size, with levels equivalent with those reported from rattlesnake round ups causing significant population decline and high probability of extinction. Taken in total, our work shows potential for persistent rattlesnake populations, but point to the need for increased understanding of several basic aspects of the snake’s natural history and provide guidance in developing future research priorities.