Abstracts (Featured Speakers)

Dr. Emily Taylor: 

Dr. Rick Shine: 

Ms. María Elena Barragán Paladines: 

Dr. Richard King: What a difference a year makes: growth, maturation, and reproductive frequency in three sympatric natricine snakes. 

Precise estimates of demographic parameters are needed to make meaningful projections of population dynamics, design management and recovery strategies, and answer fundamental questions in ecology and evolution. Among snakes, even such basic traits as age at first reproduction and reproductive frequency are sometimes poorly known, yet their impacts on population growth can be dramatic. In this talk, I describe demographic analyses of sympatric populations of Dekay’s Brownsnake (Storeria dekayi), Red-bellied Snake (S. occipitomaculata), and Common Gartersnake (Thamnophis sirtalis) based on a 10-year capture-mark-recapture study in northern Illinois. I focus on size and age at first reproduction and reproductive frequency and compare my results with published values to document uncertainty and among-population variability. In addition, I evaluate the impact these parameters can have on population projections and on imputed values of other demographic parameters. I determined size at maturity from the minimum snout-vent length (SVL) of males from which sperm was detected and the minimum SVL of gravid females. I related size at maturity to chronological age from analysis of growth in known-age individuals to determine age at first reproduction. I estimated reproductive frequency from recapture histories, proportions of gravid females, and the relationship between reproductive status and SVL. Growth and attainment of reproductive maturity was sufficiently rapid that >50% of males and females may first reproduce at two years of age in all three species. Reproductive frequency was nearly annual among female Brownsnakes and Red-bellied snakes but was less than annual in gartersnakes. A one year difference in age at first reproduction can have large impacts on population projections, potentially resulting in overly optimistic or pessimistic assessments of conservation status and management actions.