Founder Effects, Density, and Droughts Alter the Demographic Responses in Insular Elephant Populations

ABSTRACT Wildlife populations are regulated by immigration and emigration, as well as birth and death rates. When dispersal is not possible due to land use changes, population size is determined solely by births and deaths. Such is the case in many of South Africa's protected areas, where wildlife populations are well protected, intensively managed, and provided with artificial water sources, food, and custodial care. We used African savanna elephant ( Loxodonta africana ) populations in the Pilanesberg and Madikwe Nature Reserves, South Africa, as case studies to evaluate demographic responses to high density, insularity, and founder effects, especially during drier‐than‐normal periods. The incomplete age and sex structures of these founding elephant populations, combined with high age‐specific survival and fertility rates, led to transient dynamics and sustained high growth rates for an entire generation. The effect of adult survival on the modelled transient growth was greater than age at first calving or fecundity. However, the survival of weaned calves and juveniles made the most significant contribution to the transient dynamics in response to the recent dry conditions. Fences prevented dispersal and inhibited the density‐dependent mechanisms that typically stabilise growth near zero, as is the case when elephants can disperse and experience a range of resource gradients. Instead, we illustrate how density‐dependent demographic processes in the two elephant populations are already affecting their long‐term growth, including decreases in weaned calf and juvenile survival, increases in the age of first calving, and lower fecundity. These demographic signals should provide the basis for evaluating the population consequences of management interventions aimed at addressing the socio‐ecological impacts of elephants.