Matrix population models for understanding the dynamics and regulation of a Richardson’s ground squirrel population

Matrix population models provide a flexible and rigorous framework for understanding the dynamics and regulation of biological populations. We applied an age-structured matrix population model to long-term (1987-2000) demographic data to elucidate demographic and environmental causes of temporal dynamics of a population of Richardson’s ground squirrel in southern Alberta, Canada. The projected annual population growth rate ranged from 0.35 (1994-1995) to 2.63 (1999-2000), indicating substantial temporal variation in population dynamics. Prospective elasticity analysis revealed that fertility rates were potentially the most influential demographic variables; sum of fertility elasticities ranged from 0.61 to 0.85. Retrospective analysis of life-table response experiments (LTRE) revealed that changes in fertility rates, particularly of younger females, made the largest positive contributions when population growth rates increased and largest negative contributions when population growth rates decreased. Although survival rates exhibited substantial temporal variation, their contributions to observed changes in population growth rates were always smaller than those of fertility rates. Implications of these findings are discussed relative to the dynamics and regulation of our study population.