Precipitation, vegetation productivity, and human impacts control home range size of elephants in dryland systems in northern Namibia

Abstract

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 variation 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 sites in Namibia, along a gradient of precipitation and human impact, and investigated how these gradients influence the home range size on regional and site scales. Additionally, we estimated the time individuals spent within protected area boundaries. The mean 50% autocorrelated kernel density estimate for home range was 2200 km2 [95% CI:1500–3100 km2]. Regionally, precipitation and vegetation were the strongest predictors of home range size, accounting for a combined 53% of observed variation. However, different environmental covariates explained home range variation at each site. Precipitation predicted most variation (up to 74%) in home range sizes (n = 66) in the drier western sites, while human impacts explained 71% of the variation in home range sizes (n = 10) in Namibia's portion of the Kavango‐Zambezi Transfrontier Conservation Area. Elephants in all study areas maintained high fidelity to protected areas, 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, some elephants are experiencing changes in space use due to human modification.

A Snapshot into the Lives of Elephants: Camera Traps and Conservation in Etosha National Park, Namibia

“…Regardless, camera trap methodology provides a greater potential for exploring elephant grouping patterns in even greater detail, especially when expanded to include additional years of data or locations of camera trap placements. Overall, we show that our grouping patterns results align with previous research in ENP [2,5,10,[27][28][29] and similar climatic regions [42][43][44]. Additionally, our excellent observer reliability results further support the potential of continuing to include non-specialist observers, such as undergraduate research assistants, in conservation efforts.…”

“…Male, family, and mixed groups were larger and occurred in proportionally higher numbers during the dry season than the wet season (Figures 3 and 4), contrasting findings in Amboseli [45]. Elephants appear to be heavily relying on other water sources during the wet season, likely staying near ephemeral water and preferred vegetation [10], and only seeking out permanent water sources, such as Mushara, during the dry season [2,5,10,29]. Further, while Etosha's elephant home-range sizes are larger during higher rainfall conditions [2,5], Mushara might still be out of range of preferred resources for many family groups.…”

“…Elephant movement and grouping patterns vary widely across Africa. They depend on region, protected area status, rainfall, habitat fragmentation, season, perceived risk, sex, and dominance status [1][2][3][4][5][6][7][8][9][10][11][12]. Much of this research has largely relied on GPS tracking collars and aerial surveys.…”

“…Our research uses camera trap methodology to study elephants in Etosha National Park (ENP) in Namibia, expanding our knowledge of ENP's elephant grouping patterns year-round. In ENP, much of the previous work on elephant movement and grouping patterns was conducted with GPS collars [2,5,10,[27][28][29], aerial surveys [4,30], and satellite telemetry [4]. Despite all that is known about ENP's elephant movement patterns, ENP covers a large area with a population of over 2900 elephants [30].…”

Ranging behaviours across ecological and anthropogenic disturbance gradients: a pan-African perspective of giraffe ( Giraffa spp . ) space use

“…Our systematic study of giraffe ranging behaviours using GPS telemetry data provided home range estimates larger than most other previously reported across all giraffe taxa [36,40,42,43,70–74]. Compared to other large-bodied herbivores, these giraffe home range estimates are generally smaller than African bush elephants ( Loxodonta africana ) across a wide range of systems [75], but larger than reported home range values for African buffalo ( Syncerus caffer ) [76], greater kudu ( Tregelaphus strepsiceros ) [72] and significantly larger than home range size reported for the temperate red deer ( Cervus elaphus ) [77–79]. Moreover, we found significant ecological and anthropogenic effects on space use across their range.…”