Management of a Geometric Tortoise (Psammobates geometricus) Population in a High-Risk, Fire-Prone Landscape

Abstract. We began developing our Geometric Tortoise Ecosystem Preserve in 2015. At the same time, we began a mark–recapture study to detect changes in the population size through time to inform our management practices. We now have data through 2021. Mark–recapture analysis gives a population size of between 800 and 1200 individuals. It is the last remaining substantial population. Using Lande's classification of 1933 of stochastic influences on demography, we find that 1) demographic stochasticity is not a problem, as the population is large enough and consists of individuals whose home ranges overlap; 2) environmental stochasticity is important mainly through variations in annual rainfall, including severe droughts; and 3) catastrophes occur in the form of wildfire that can destroy a local population. Taken together, these environmental effects can cause large changes in population size, making this species at risk of local extinction. If it were to go extinct, there are no other adjacent populations that could be used to recolonize our preserve. Therefore, we conclude that head starting is necessary to safeguard the population.