Annual proportions of illegally killed elephants (PIKE): The rate among found carcasses of illegally killing was greatest during the last three years of the study.

<p>Annual proportions of illegally killed elephants (PIKE): The rate among found carcasses of illegally killing was greatest during the last three years of the study.</p

Comparative Demography of an At-Risk African Elephant Population

<div><p>Knowledge of population processes across various ecological and management settings offers important insights for species conservation and life history. In regard to its ecological role, charisma and threats from human impacts, African elephants are of high conservation concern and, as a result, are the focus of numerous studies across various contexts. Here, demographic data from an individually based study of 934 African elephants in Samburu, Kenya were summarized, providing detailed inspection of the population processes experienced by the population over a fourteen year period (including the repercussions of recent increases in illegal killing). These data were compared with those from populations inhabiting a spectrum of xeric to mesic ecosystems with variable human impacts. In relation to variability in climate and human impacts (causing up to 50% of recorded deaths among adults), annual mortality in Samburu fluctuated between 1 and 14% and, unrelatedly, natality between 2 and 14% driving annual population increases and decreases. Survivorship in Samburu was significantly lower than other populations with age-specific data even during periods of low illegal killing by humans, resulting in relatively low life expectancy of males (18.9 years) and females (21.8 years). Fecundity (primiparous age and inter-calf interval) were similar to those reported in other human impacted or recovering populations, and significantly greater than that of comparable stable populations. This suggests reproductive effort of African savanna elephants increases in relation to increased mortality (and resulting ecological ramifications) as predicted by life history theory. Further comparison across populations indicated that elongated inter-calf intervals and older ages of reproductive onset were related to age structure and density, and likely influenced by ecological conditions. This study provides detailed empirical data on elephant population dynamics strongly influenced by human impacts (laying the foundation for modeling approaches), supporting predictions of evolutionary theory regarding demographic responses to ecological processes.</p> </div

Indices of the age of reproductive onset: (a) Cumulative hazard rate for female primparous age (dotted line) and male dispersal (solid line) in the Samburu population.

<p>Indices of the age of reproductive onset: (a) Cumulative hazard rate for female primparous age (dotted line) and male dispersal (solid line) in the Samburu population.</p

African elephant demographic parameters from 12 wild populations (one sampled twice) collected through individual registration, radio tracking or culling.

<p>African elephant demographic parameters from 12 wild populations (one sampled twice) collected through individual registration, radio tracking or culling.</p

Map of the Samburu and Buffalo Springs National Reserves in Kenya, East Africa.

<p>Map of the Samburu and Buffalo Springs National Reserves in Kenya, East Africa.</p

Summary of age class fecundity: (a) Age specific fecundity (m_x) (dashed line = actual, and solid line = 5-year running average) peaked when the Samburu females were in their mid 40s.

<p>(b) Age specific reproductive value (v_x) (dashed line = actual, and solid line = 5-year running average) declined after the peak between 15 and 20 years of age.</p

Female (green) and male (red) survivorship in the Dzanga population (shaded areas show point-level 95% CI).

<p>Females were generally twice as likely to survive to a given age as were males.</p

Annual Samburu population demography and population trend: (a) The number of births (black bars), deaths (gray bars), and the population size at the end of each year.

<p>(b) The population mortality and natality varied annually the duration of the study. Natality pulses every 3–4 years are a function of the prolonged (22 month) gestation period of elephant resulting in multi-year inter-calving intervals.</p

Female reproductive value.

<p>Female reproductive value.</p

Demography of a forest elephant population

<div><p>African forest elephants face severe threats from illegal killing for ivory and bushmeat and habitat conversion. Due to their cryptic nature and inaccessible range, little information on the biology of this species has been collected despite its iconic status. Compiling individual based monitoring data collected over 20 years from the Dzanga Bai population in Central African Republic, we summarize sex and age specific survivorship and female age specific fecundity for a cohort of 1625 individually identified elephants. Annual mortality (average = 3.5%) and natality (average = 5.3%) were lower and markedly less variable relative to rates reported for savanna elephant populations. New individuals consistently entered the study system, leading to a 2.5% average annual increase in the registered population. Calf sex ratios among known birth did not differ from parity. A weak seasonal signal in births was detected suggesting increased conceptions during the wet season. Inter-calf intervals and age of primiparity were longer relative to savanna elephant populations. Within the population, females between the ages of 25–39 demonstrated the shortest inter-calf intervals and highest fecundity, and previous calf sex had no influence on the interval. Calf survivorship was high (97%) the first two years after birth and did not differ by sex. Male and female survival began to differ by the age of 13 years, and males demonstrated significantly lower survival relative to females by the age of 20. It is suspected these differences are driven by human selection for ivory. Forest elephants were found to have one of the longest generation times recorded for any species at 31 years. These data provide fundamental understanding of forest elephant demography, providing baseline data for projecting population status and trends.</p></div