Differential influence of human impacts on age-specific demography
underpins trends in an African elephant populationGeorge Wittemyer, David
Daballen & Iain Douglas-HamiltonEcosphereAugust 9, 2021 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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LINKhttps://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecs2.3720
https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecs2.3720