Abstract:
California is home not only to many endangered species, but also to entire ecosystems that are threatened by human activities such as urbanization and irrigation. One such “hotspot” of species endangerment is in Central California’s San Joaquin Valley. One approach to conserving this threatened ecosystem is to focus efforts on a species that is instrumental to the ecosystem. The giant kangaroo rat (Dipodomys ingens) is an ecosystem engineer endemic to the San Joaquin Valley, and its burrowing and grazing behaviors have tremendous effects on the arid grassland habitat. In this thesis I focus on processes that either limit or regulate giant kangaroo rat populations: available food and burrow availability. I build a discrete-time stochastic population model to examine the effects of varying the number of available burrows within an isolated community. Using rainfall as a proxy for food production, I calculate numerical results over the burrow-rainfall parameter space and find distinct equilibria that correspond to scenarios of various combinations of burrow and available food limitation. In particular, my model suggests an optimal burrow-count threshold for a given average rainfall (food availability) value. Below this threshold, each individual increase in the number of burrows increases the steady-state population size. Once the threshold is crossed, not only do new burrows not have much effect on the overall population size, but there appears to be a greater likelihood of an extinction event.
