A Population Viability Analysis for African Elephant (Loxodonta africana): How Big Should Reserves Be?

We present an age-structured, density-dependent model of elephant population dynamics in a fluctuating environment, drawing primarily upon the life history parameters obtained from studies in semi-arid land at Tsavo National Park, Kenya. Density regulation occurs by changes in the age of first reproduction and calving interval. We model environmental stochasticity with drought events affecting sex- and age-specific survivorships. Results indicate a maximum population growth rate of 3% per year and an equilibrium elephant density of 3.1/mile². Analysis of the demographic results and their sensitivity to changes in juvenile survivorship and drought frequencies, supported by genetic considerations, suggests that in semi-arid regions a minimum reserve size of 1000 mile² is necessary to attain a 99% probability of population persistence for 1000 years. The effect of age-independent culling on population viability is also analyzed.