Journal Article

Savanna elephant numbers are only a quarter of their expected values

Pimm, Stuart L., Purdon, Andrew, Robson, Ashley S., Young-Overton, Kim D., van Aarde, Rudi J., Trimble, Morgan J.

2017

Overview

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.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Analysis / Animal populations / Animals / Benchmarks / Biodiversity / Biology and Life Sciences / Census / Climate change / Conservation / Conservation of Natural Resources - statistics & numerical data / Ecological monitoring / Ecology / Ecology - statistics & numerical data / Ecology and Environmental Sciences / Ecosystem / Ecosystems / Elephants / Elephants - growth & development / Elephants - physiology / Encroachment / Endangered & extinct species / Environmental aspects / Grassland / Growth models / Loxodonta africana / Mathematical models / Monte Carlo simulation / National parks / Physical sciences / Poaching / Population / Population Dynamics - statistics & numerical data / Population ecology / Populations / Productivity / Protected areas / Research and analysis methods / Savannahs / Savannas / Time series / Trends / Water availability / Zoology