Environmental and anthropogenic factors predict elephant home range size across Namibia

Lorena Benitez, Lacey F. Hughey, Christen H. Fleming, Peter Leimgruber and Jared A. Stabach, Conservation Ecology Center, Smithsonian Conservation Biology Institute, Front Royal, VA, Werner Kilian, Etosha Ecological Institute, Namibia, George Wittemyer, Colorado State University

Background/Question/Methods
Climatic variability, resource availability, and anthropogenic impacts heavily influence an animal’s home range. This makes home range size an effective metric for understanding how variations in environmental factors alter the behavior and spatial distribution of animals. In this study, we estimated home range size of African elephants (Loxodonta africana) across four distinct study areas in northern Namibia, and examined which factors (precipitation, surface water, vegetation, protected area designation, and human impacts) best explain variation in home range size. We calculated autocorrelated kernel density estimate (AKDE) home ranges from the ctmm R package for 86 elephants tracked from 2008 to 2015. We investigated how environmental gradients influence the home range size on national and regional scales. Additionally, we estimated space use on a pixel-by-pixel basis to estimate the time individuals spent within protected area boundaries.

Results/Conclusions
The mean 50% autocorrelated kernel density estimate for home range was 2,200 km2 [95 % CI:1500-3100 km2]. There was no significant difference in home range size between individuals across study areas (P = 0.26). Within each study area, however, home range size varied widely. Across all study areas, precipitation and vegetation accounted for a combined 53% of variation in home range size. Home range variation was explained best by different environmental variables at each site. Precipitation, for instance, predicted most variation (up to 74%) in home range size in the drier western study areas (n = 66), while human impacts explained 71% of the variation in home range size in Namibia’s portion of the Kavango-Zambezi Transfrontier Conservation Area (n = 10). Elephants in all study areas maintained high fidelity to protected areas, especially national parks, spending an average of 85% of time tracked on protected lands. These results suggest that while most elephant space use in Namibia is driven by natural dynamics (e.g., precipitation), some elephants are experiencing changes in space use due to human modification. Conservation management should focus on preserving existing connectivity and habitat across all study areas, with a focus on mitigating human-elephant conflict in areas with high levels of human modification.