Poaching of African Elephants Indirectly Decreases Population Growth Through Lowered Orphan Survival

Abstract

Prolonged maternal care is vital to the well-being of many long-lived mammals. The premature loss of maternal care, i.e. orphaning, can reduce offspring survival even after weaning is complete. However, ecologists have not explicitly assessed how orphaning impacts population growth. We examined the impact of orphaning on population growth in a free ranging African elephant population, using 19 years of individual-based demographic monitoring data. We compared orphan and nonorphan survival, performed a sensitivity analysis to understand how population growth responds to the probability of being orphaned and orphan survival, and investigated how sensitivity to these orphan parameters changed with level of poaching. Orphans were found to have lower survival compared to non-orphaned age mates, and population growth rate was negatively correlated with orphaning probability and positively correlated with orphan survival. This demonstrates that, in addition to its direct effects, adult elephant death indirectly decreases population growth through orphaning. Population growth rate’s sensitivity to orphan survival increased for the analysis parameterized using only data from years of more poaching, indicating orphan survival is more important for population growth as orphan numbers increase. We conclude that orphaning substantively decreases population growth for elephants and should not be overlooked when quantifying the impacts of poaching. Moreover, we conclude that population models characterizing systems with extensive parental care benefit from explicitly incorporating orphan stages, and encourage research into quantifying effects of orphaning in other social mammals of conservation concern.

Keywords: African elephant, demography, orphan, poaching, population growth, sensitivity analysis, survival