Ecosphere (Aug 2021)
Differential influence of human impacts on age‐specific demography underpins trends in an African elephant population
Abstract
Abstract Diagnosing age‐specific influences on demographic trends and their drivers in at‐risk wildlife species can support the development of targeted conservation interventions. Such information also underpins understanding of life history. Here, we assess age‐specific demography in wild African elephants, a species whose life history is marked by long life and extreme parental investment. During the 20‐yr study, survival and its variation were similar between adults and juveniles in contrast to relationships found among many large‐bodied mammals. Prospective analysis on age‐specific Leslie matrices for females demonstrated survival is more influential than fecundity on λ, with sensitivity of both decreasing with age. Results aggregated by stage classes indicate young adults (9–18 yr) demonstrated the highest elasticity, followed by preparous juveniles (3–8 yr). Mature adults (36+ yr) had the lowest aggregate elasticity value. Retrospective analysis parameterized by data from the early and latter periods of the study, characterized by low then high human impact (faster and slower growth, respectively), demonstrated fecundity (particularly for adults; 19–35 yr) explained the greatest variation in λ observed during the period of low human impact, while survival (particularly juvenile and adult) was more influential during the high human impact period. The oldest females (mature adult stage) weakly influenced population growth despite demonstrating the highest fecundity and their behavioral importance in elephant society. Multiple regression models on survival showed the negative effects of human impacts and population size were the strongest correlates across sexes and ages. Annual rainfall, our metric for environmental conditions, was weakly informative. The presence of dependent young was positively correlated with survival for breeding females, suggesting condition‐based mortality filtering during pregnancy. Notwithstanding the stabilizing effect of high juvenile survival on elephant population growth, demographic processes in elephants were similar to those shaping life history in other large herbivores. Implications of the study results with respect to the conservation of elephants and analysis of demographic impact of poaching are discussed, along with the study's relevance to theories regarding the evolution of life history and parental care.
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