Demographic responses of an insular elephant population to removal as a management intervention

Abstract

Disturbances that change population structure may evoke transient dynamics that can be assessed within a demographic resilience framework. Conservation management interventions are conceptually disturbances that can be evaluated through such a framework to inform management actions and goals. The Main Camp in Addo Elephant National Park in South Africa presents a case study. Here management reduced the size of the elephant (Loxodonta africana) population by 26%. We compared population growth, modelled trends, constructed life tables and parameterized population projection matrices from data collected before, during and after the interventions. The interventions reduced population size and density, but co-occurring droughts may have reduced subsequent population growth and stage-specific survival. Transient dynamics followed the interventions and droughts and were associated with an unstable stage structure. The effect of adult survival on modelled asymptotic growth (its elasticity) was greater than a change in fertility. However, lowered juvenile survival contributed most to changes in transient growth. Management plans for elephant populations should consider the length of transients induced by interventions and environmental disturbances such as droughts. Our approach can benefit the assessment of population responses of elephants to disturbances such as poaching and persistent droughts elsewhere in Africa.