VARIATION IN DEMOGRAPHY OF TURTLES IN A SEMI-ARID LANDSCAPE, WITH AN EMPHASIS ON THE ANNUAL SURVIVAL OF YELLOW MUD TURTLE POPULATIONS
McVay, Trevor James
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Turtle species are declining rapidly across the world because of factors such as habitat degradation, overharvest, and climate change. These declines coupled with a lack of knowledge on many species’ life history and factors that directly affect their populations has led to sparse backing for management and conservation. The use of annuli as an aging technique can lead to quick, targeted research in order to fill these gaps within the literature for species of concern. However, there is disagreement within the scientific community of the use of this technique because some researchers have questioned its validity. Therefore, I examined the variation in annual survival, growth rates, and sex ratios of yellow mud turtle (Kinosternon flavescens) populations at 9 sites within the species’ range in Texas. I also compared survival estimates from age data using annuli to commonly used estimates within the scientific community on both these populations and a population of ornate box turtles (Terrapene ornata) to examine the techniques utility. From 2003 to 2016, a total of 2,428 captures of 1,629 individual yellow mud turtles were obtained, and 930 captures of 637 individual ornate box turtles were collected. The annual survival estimates (62.2%-85.6%) and sex ratios varied amongst the different sites, but the growth rates were not significantly different among all of the sites for yellow mud turtles. For the ornate box turtle population, annual survival was calculated to be 72.3% using a Jolley-Seber capture-mark-recapture estimate, 79.4% with age-structured regression, and 80.75% using a Kaplan-Meier procedure for radio telemetry data. Rainfall, climate, and nutrition in relation to growth rates did not display to have a direct influence on the varying annual survival in the different study sites for yellow mud turtles. Biased sex ratios had a slight relationship with the annual survival rates with sites estimated to have lower survival displaying these biases, but this could be influenced by weaker data sets of some of the study site. Predator abundance and permanence of aquatic habitat are hypothesized to be possible causal factors for annual survival rate differences, but must be researched in the future. The biased sex ratios at the given sites are hypothesized to be influenced by the differential mortality amongst sexes at these sights. Compared to other literature, the Matador WMA ornate box turtle population displayed a lower than average survival rate causing them to be a population of particular concern. When comparing survival estimation of annuli analysis to accepted methods within the scientific community, CMR data and annuli data estimate differences were less than 1.1% in yellow mud turtles. The ornate box turtle annual survival estimate differences were less than 1.35% between data from CMR, radio telemetry, and annuli analysis. These similarities amongst estimates argue for the utility of annuli as a good estimate of age structure for turtle species and provide significant backing for the use of annuli analysis as an estimate of survival.