Size and Age Structure of a Population of Western Terrestrial Garter Snakes (Thamnophis elegans)

Abstract

The age structure of a population can reveal trends in growth and maturation and be used to describe other demographic processes. Accurate descriptions of age structure for populations of snakes are rare, limiting our ability to understand their population dynamics. In this study, I used skeletochronology to determine the age of individuals, and examined the relationship between age and size, in a population of western terrestrial garter snakes (Thamnophis elegans). Most of the adult snakes had between two and six growth layers, and the youngest gravid female had three growth layers. Although lengths and number of growth layers were positively correlated, it would not be possible to predict the age of an individual from its length. DETERMINATION of the age of individual animals is an important component of the study of populations, because demographic processes (e.g., fecundity and survivorship) can be age specific. Knowledge of age structure therefore can yield essential data on the dynamics of the population and life history of the species as a whole (Parker and Plummer, 1987). Individual and population-specific patterns of growth and maturation, and individual and year-specific variations in these patterns, also can be determined if age structure is known; this information allows the dynamics of populations to be modeled and projected into the future more accurately. Besides contributing to our understanding of the fundamental ecological issue of limitation of distribution and abundance, such knowledge is critical to management or conservation plans for many species. Accurate data on age rarely have been collected for populations of snakes, greatly limiting our understanding of their population dynamics and life histories.