Life and death in a corn desert oasis: reproduction, mortality, genetic diversity, and viability of Illinois' last Eastern Massasauga population

Biodiversity is being lost at an unprecedented rate globally, with the primary driver being habitat loss and fragmentation. As natural habitats contract, species are forced into small often fragmented populations at increased risk of extirpation. Reptile species are thought to be experiencing wide-spread declines, the extent of which may be underestimated due to lack of long-term data for most species. Snakes, especially venomous species, are particularly vulnerable because of their life-history characteristics and often specialized habitat requirements. Unfortunately, snakes are also under-studied due in part to a historical lack of interest in the taxa and the difficulty with finding large numbers of individuals. The Eastern Massasauga (Sistrurus catenatus) is a rattlesnake species native to prairie/grassland and bog habitats from Iowa to New York and Ontario, Canada. The Eastern Massasauga is experiencing range-wide declines primarily caused by anthropogenic habitat conversion to agriculture and was recently proposed for listing as threatened under the Federal Endangered Species Act. In Illinois, only one Eastern Massasauga population remains extant, located at Carlyle Lake, Clinton County. Capture-mark-recapture monitoring of the Carlyle Lake population has been ongoing since 1999, and radio-telemetry was conducted from 2001-2003 and 2009-2011, providing a rare long-term data set for use in conservation planning. To evaluate conservation issues in the Illinois Eastern Massasauga population, I used the long-term data set to evaluate three aspects of population biology that are of concern in small populations: population genetics, reproduction, and mortality. I then integrated those data with a population viability and sensitivity analysis to determine the population trajectory, identify which demographic parameters have the greatest impact on population persistence, and make conservation strategy recommendations. Despite being both small and isolated, the Carlyle Lake Eastern Massasauga population exhibits moderate genetic diversity, no inbreeding or evidence of recent genetic bottlenecks, but low effective population size. Thus, conservation planning should consider genetic factors, but immediate intervention specific to genetic concerns is not necessary. Reproductive output in the Eastern Massasauga is not constrained by female body size, and there is no evidence of a trade-off between offspring size and number. Reproductive output, therefore, appears to be resource dependent and has the potential to increase via targeted conservation actions. Mortality of Eastern Massasaugas is caused primarily by automobiles and predation. Seasonal or permanent closure of non-essential roads and reduction of small carnivore numbers could decrease mortality at Carlyle Lake and positively impact population persistence. Finally, the population viability analysis indicated a positive population growth rate, but also a 65% probability of extinction in 50 years. Sensitivity analyses show that reproductive characteristics (proportion of breeding females, litter size, and offspring sex ratio) and carrying capacity have the greatest impact on population trajectory. Thus, conservation strategies for the Eastern Massasauga should focus on restoring additional habitat to increase carrying capacity, and use more manipulative measures only if the population growth rate becomes negative. This study provides an important application of long-term data for the conservation of an imperiled snake species and functions as a surrogate for other Eastern Massasauga populations or species with similar life histories for which detailed data are not available