Jenkins, C.L., J.M. Bauder, and C.R. Peterson. 2017. Population level consequences of microgeographic variation in Great Basin rattlesnake reproduction and survival. Pages 143-153 in M.J. Dreslik, W.K. Hayes, S.J. Beaupre, and S.P. Mackessy, editors. Biology of the Rattlesnakes Vol. II. ECO Herpetological Publishing and Distribution, Rodeo, New Mexico, USA.
Abstract
Rattlesnake species living in extreme environments often have life histories that make them especially susceptible to disturbance. There are many studies of rattlesnake life histories but few that link life histories and population biology. A recent study on three Western Rattlesnake populations in close proximity showed that life history characteristics such as age to maturity, body condition, growth, pregnancy intervals, fecundity, and size of offspring varied among populations; specifically that one population consistently had values indicating low reproductive output. In this study, our goal was to determine if the observed microgeographic variation in reproduction has population-level consequences. To achieve this, we used a 17-yr Western Rattlesnake mark-recapture dataset to estimate age-specific survival rates and subsequently combined them with reproductive characteristics to estimate population growth rates for each population. Survival rates varied interactively by age (i.e., adults had the highest survival) and population and over time albeit in no consistent manner. Survival rates also showed a microgeographic pattern consistent with previously published variation in reproductive characteristics. The population with reproductive values suggesting lower reproductive output, Crater Butte, also had the lowest overall survival rates. However, neonates at Crater Butte had the highest survival of neonates at the three sites. Population growth rates suggest that females from Crater Butte are not replacing themselves and that the population is declining by approximately 7% per year whereas females from the other two populations are replacing themselves and their populations are approximately stable. Results from this study show that microgeographic variation in reproduction and survival can have population-level consequences. Future studies should examine the factors that cause microgeographic variation in rattlesnake reproduction and ultimately population biology.