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Devastating Decline of Forest Elephants in Central Africa

Fiona Maisels et al. PLoS One.

Abstract

African forest elephants- taxonomically and functionally unique-are being poached at accelerating rates, but we lack range-wide information on the repercussions. Analysis of the largest survey dataset ever assembled for forest elephants (80 foot-surveys; covering 13,000 km; 91,600 person-days of fieldwork) revealed that population size declined by ca. 62% between 2002-2011, and the taxon lost 30% of its geographical range. The population is now less than 10% of its potential size, occupying less than 25% of its potential range. High human population density, hunting intensity, absence of law enforcement, poor governance, and proximity to expanding infrastructure are the strongest predictors of decline. To save the remaining African forest elephants, illegal poaching for ivory and encroachment into core elephant habitat must be stopped. In addition, the international demand for ivory, which fuels illegal trade, must be dramatically reduced.

Conflict of interest statement

Competing Interests: The authors have the following interest: This study was in part supported by the following: Busch Gardens and TOTAL Gabon. CIB (Congolaise Industrielle du Bois) provided some logistical help for the 2006 and 2010–11 surveys in the following northern Congo sites (Pokola, Kabo, Loundougou. This does not alter the authors’ adherence to all the PLOS ONE policies on sharing data and materials, as detailed online in the guide for authors.

Figures

Figure 1
Figure 1. Elephant dung density and range reduction across the Central African forests.
Predictions are shown for (A) 2002 and (B) 2011 for the model with variables: survey year∧, Human Influence Index***, corruption*** and the presence/absence of guards***, and (C) 2002 and (D) 2011 for the model with variables: survey year∧, proximity to road∧, human population density***, corruption*** and the presence/absence of guards*** (P-values are: ‘***’ <0.001 and ‘∧’ <0.1). Increasingly darker shades of green correspond to higher densities, grey represents extremely low elephant density range (the first interval: 0–100 elephant dung piles/km2) and white is non-habitat (80 survey sites outlined in red). Cutpoints are: 0; 100; 250; 500; 1,000; 1,500; 3,000; 5,000; and 7,500 dung piles/km2. Countries 1–5 are: Cameroon; Central African Republic; Republic of Congo; DRC; Gabon.
Figure 2
Figure 2. Estimated change in elephant dung density (/km2) distribution during 2002–2011 across the Central African forests.
Results are shown as a percentage of the total area of potential elephant habitat overall (A & B) and by country (C & D) for the predictive model with variables: (A & C) survey year, Human Influence Index, corruption and the presence/absence of guards, and (B & D) survey year, proximity to road, human population density, corruption and the presence/absence of guards. The dung density (per km2) intervals are unequal and correspond to the following elephant population categories: extremely low density (0–100), very low (100–250), low (250–500), medium (500–1,000), high (1,000–3,000) and very high (3,000–7,500). With the loss of very high elephant populations in 2011, there is a significant shift into the lower density intervals over the nine years.
Figure 3
Figure 3. Estimated conditional dependence of elephant dung density for top-ranked multi-variable models including hunter sign.
Results are shown for the top-ranked model with variables: (A) hunter sign*, (B) survey year*, (C) proximity to roads∧, (D) human population density***, (E) corruption*** (higher values = less corrupt) and presence/absence of guards***. Also shown is (F) the Human Influence Index (HII) for the model with proximity to road and human population density variables replaced by the HII, i.e. one of the top-ranking models with variables: hunter sign**, survey year*, HII*, corruption***, and presence/absence of guards***. P-value significance codes are: ‘***’<0.001, ‘**’<0.01, ‘*’<0.05, and ‘∧’<0.1. Plot components are: Estimates on the scale of the linear predictor (solid lines) with the y-axis scale for each variable selected to optimally display the results, confidence intervals (dashed lines), and explanatory variable values of observations with a focus on the core 95% of values for hunter sign, proximity to road and human population density (rug plot - short vertical bars along each x-axis showing the x value for each site).
Figure 4
Figure 4. Boxplots of indices of elephant abundance and hunting intensity.
Summaries shown are the natural logarithm of: (A) elephant dung encounter rate per 100 km grouped by the presence/absence of wildlife guards, (B) elephant dung encounter rate per 100 km grouped by the level of hunting intensity (group cutpoints are 0.6 and 1.75 hunter sign/km), and (C) hunter-sign frequency per 100 km grouped by the presence/absence of wildlife guards. Box-widths are proportional to the number of observations in each group.
Figure 5
Figure 5. Encounter rate of elephant dung per kilometre.
Results are shown for the 80 survey sites in Central Africa included in this study. Grey shading represents forest cover.
Figure 6
Figure 6. Encounter rate of hunter sign per kilometre.
Results are shown for the 80 survey sites in Central Africa included in this study. Grey shading represents forest cover.
Figure 7
Figure 7. Percentage breakdown of the total number of forest elephants by country.
Results are shown for 3 time periods: pre-1970s and 1989 and 2011 (this study).

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Publication types

Grant support

For funding of the survey work the authors thank (in alphabetical order) Nancy Abraham, the African Wildlife Foundation, Beneficia Foundation, Busch Gardens, Columbus Zoo, Conservation International, Daniel K. Thorne Foundation, Diane Fossey Gorilla Foundation International, Espèces Phares (European Union), Ecosystèmes Forestiers d’Afrique Centrale (ECOFAC), Fauna and Flora International, Frankfurt Zoological Society, IUCN Netherlands, John D. and Catherine T. MacArthur Foundation, KFW, LifeWeb (Spain), National Fund for Scientific Research (FNRS, Belgium), Offield Family Foundation, Operation Loango, Prince Bernhard Wildlife Fund, RAPAC, The Arcus Foundation, The Aspinall Foundation, The Born Free Foundation, The Institute for Biodiversity and Ecosystem Dynamics at The University of Amsterdam, The Jane Goodall Institute, The Liz Claiborne and Art Ortenberg Foundation, The Lucie Burgers Foundation, The Wasmoeth Wildlife Foundation and Karl Ammann, Total Gabon, United States Agency for International Development (USAID CARPE), USFWS Great Ape Conservation Fund, USFWS African Elephant Conservation Fund, Wildlife Conservation Society, World Wildlife Fund and the Zoological Society of London. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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