Demography of a forest elephant population

RESEARCH ARTICLE Demography of a forest elephant population Andrea K. Turkalo1,2, Peter H. Wrege2, George Wittemyer3,4* 1 The Wildlife Conservation Society, B.P., Bangui, Central African Republic, 2 The Elephant Listening Project, Bioacoustics Research Program, Cornell Lab of Ornithology, Ithaca, New York, United States of America, 3 Department of Fish, Wildlife and Conservation Biology, Colorado State University, Fort Collins, Colorado, United States of America, 4 Save The Elephants, Nairobi, Kenya * Abstract a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Turkalo AK, Wrege PH, Wittemyer G (2018) Demography of a forest elephant population. PLoS ONE 13(2): e0192777. https:// doi.org/10.1371/journal.pone.0192777 Editor: Alfred L. Roca, University of Illinois at Urbana-Champaign, UNITED STATES Received: October 12, 2017 Accepted: January 30, 2018 Published: February 15, 2018 Copyright: © 2018 Turkalo et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: US Fish and Wildlife Service International Conservation Grant; Elephant Listening Project support. Competing interests: The authors have declared that no competing interests exist. 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. Introduction Information on the reproductive and mortality schedules of species is fundamental for investigation of life history strategies [1, 2] as well as for diagnosing the conseravtion status of populations [3]. Such information is notoriously difficult to collect and, therefore, available only for a select number of species and populations, disporportionately represented by species of economic interest [4]. While use of data from closely related species can serve as a useful proxy for demographic modeling, such approaches can be misleading or provide weak inference PLOS ONE | https://doi.org/10.1371/journal.pone.0192777 February 15, 2018 1 / 17 Forest elephant demography regarding the drivers of actual population change [5, 6]. As such, compiling demographic information on species of interest is of high priority, particularly in respect to the development of population monitoring and conservation intervention programs for at risk species. Collection of high resolution demographic data is particularly challenging for rare or cryptic species that utilize large ranges. While non-invasive methods for modeling spatial distribution and occupancy can provide insight into densities and population trends, such approaches often offer limited insight into the processes driving change or for identifying segments of a population experiencing the greatest threat [7]. To determine such information, individual based monitoring using remote telemetry (e.g. mark-recapture approaches using radio collars sensu [8]), genetic screening [9], or individual identification and monitoring projects [10] are powerful approaches. Longitudinal sampling of known cohorts of individuals, in particular, can provide rich information on population processes, that can serve to identify underlying mechanisms of change and greater insight to demography, life history and behavior (e.g., [11]). While highly valuable for these reasons, few long term, individually based studies exist given logistical difficulties of conducting such work in wild settings [10]. The forest elephants (Loxodonta cyclotis) of Central Africa are of high conservation concern due to their ecological importance in forest ecosystems [12], evolutionary distinctiveness [13, 14], and large scale range and catastrophic decline [15, 16]. Forest elephants fulfill fundamental ecological roles structuring vegetation in central African humid forests, the second largest contiguous forest block on earth and an important carbon sequestration zone [17]. Forest elephants are a dominant engineer of their forest landscapes, being a primary seed disperser [18, 19] and generating clearings and trails relied on by many forest animals [20]. Across their range in the Congo Basin, forest elephants are threatened primarily by poaching and increasing competition from an expanding human population [15, 16]. A recent analysis of forest elephant census data across their range shows a 62% decrease in their numbers for the period of 2002–2011 coupled with a loss of 30% of their geographical range [15]. Despite the severe threats faced by forest elephants and recent work providing insight to the bai use patterns and basic demography [6, 21], knowledge gaps of the behavior and age specific demography of this species remain. These gaps limit our understanding of its conservation status and ability to develop comprehensive conservation strategies and management programs. Our attempts to predict forest elephant demographic response to large scale decline are modeled off information generated from a handful of intensively studied populations of savannah elephants (Loxodonta africana) [11, 22–25]. It (...truncated)