Savanna elephant numbers are only a quarter of their expected values

Abstract

Savannas once constituted the range of many species that human encroachment has now reduced to a fraction of their former distribution. Many survive only in protected areas. Poaching reduces the savanna elephant, even where protected, likely to the detriment of savanna ecosystems. While resources go into estimating elephant populations, an ecological benchmark by which to assess counts is lacking. Knowing how many elephants there are and how many poachers kill is important, but on their own, such data lack context. We collated savanna elephant count data from 73 protected areas across the continent estimated to hold ~50% of Africa’s elephants and extracted densities from 18 broadly stable population time series. We modeled these densities using primary productivity, water availability, and an index of poaching as predictors. We then used the model to predict stable densities given current conditions and poaching for all 73 populations. Next, to generate ecological benchmarks, we predicted such densities for a scenario of zero poaching. Where historical data are available, they corroborate or exceed benchmarks. According to recent counts, collectively, the 73 savanna elephant populations are at 75% of the size predicted based on current conditions and poaching levels. However, populations are at <25% of ecological benchmarks given a scenario of zero poaching (~967,000)—a total deficit of ~730,000 elephants. Populations in 30% of the 73 protected areas were <5% of their benchmarks, and the median current density as a percentage of ecological benchmark across protected areas was just 13%. The ecological context provided by these benchmark values, in conjunction with ongoing census projects, allow efficient targeting of conservation efforts.

African Environmental Change from the Pleistocene to the Anthropocene

“…Megafauna in general capture the problems of multispecies coexistence in the Anthropocene: Even with recognition of their ecological value, desires to conserve populations can conflict with available conservation land (139). The conservation statuses of many African megafauna are on a declining trajectory today (108,109), with rapid population declines in both megacarnivores (125,140) and megaherbivores (141,142). The threats include not only hunting (119,120), but also fencing and habitat destruction or fragmentation stemming from human activity (124,125,143).…”

Big cats at large: Density, structure, and spatio‐temporal patterns of a leopard population free of anthropogenic mortality

“…Consequently, the densities at which carnivore populations occur naturally often remain unknown. Such estimates could be used to establish the ecological carrying capacity of populations (e.g., Hayward, O'Brien, & Kerley, ; Karanth, Nichols, Kumar, Link, & Hines, ), set conservation targets (e.g., Robson et al, ; Wikramanayake et al, ) and gain insight into the dynamics and determinants (i.e., by “top‐down” or “bottom‐up” processes) of carnivore populations in the absence of anthropogenic pressure (Wallach et al, ).…”

Informing Aerial Total Counts with Demographic Models: Population Growth of Serengeti Elephants Not Explained Purely by Demography

“…), a young age structure, and densities much lower than those observed in some areas (Robson et al . ). The Mara elephant population has remained relatively stable in size during the past 15 years, with higher densities than the relatively unpopulated Serengeti (Figure A).…”

“…Examples of distributional shifts by elephants in response to human disturbances have been well-documented in other ecosystems (Douglas-Hamilton 1987;Graham et al 2009;Goheen and Palmer 2010). Nonetheless, the Serengeti and the Mara populations are undergoing a period of rapid in situ growth, evidenced by relatively low elephant carcass ratios compared to many ecosystems in Africa (Chase et al 2016), a young age structure, and densities much lower than those observed in some areas (Robson et al 2017). The Mara elephant population has remained relatively stable in size during the past 15 years, with higher densities than the relatively unpopulated Serengeti ( Figure 1A).…”