Abstract
AbstractAimAfrican elephants are ecosystem engineers. As such, their long‐term patterns of distribution and abundance (i.e., space‐use intensity) will influence ecosystem structure and function. We elucidate these patterns for bull versus herd groups, by analysing the spatiotemporal dynamics of an increasing elephant population in relation to key ecological drivers: rainfall, distance to major rivers and time since last fire. Significant changes to the long‐term patterns of elephant density and group‐type probabilities are identified and explained.LocationKruger National Park, South Africa.MethodsUsing almost three decades of census records (1985–2012), we applied Multiple Point Process Models to assess the influence of rainfall, rivers and fire in shaping elephant space‐use. Significant changes to the long‐term patterns of elephant density and group type were also identified using kernel density estimates and the spatially varying probability of encountering either bull or herd group.ResultsBull and herd groups are no longer clearly segregated as available empty space becomes more limited. Bull and herd groups have dichotomous resource selection functions, in that bulls concentrate in areas receiving lower rainfall but more frequent fires while herds concentrate in higher rainfall areas experiencing less frequent fires. Both bull and herd groups concentrate closer to major rivers, emphasizing rivers as important spatial drivers. Overall, densities increased most significantly closer to rivers and in areas experiencing fewer fires. Fire was also a strong agent of group‐type change, as the probability of finding bulls, contrary to herds, significantly increased as fire return periods shortened.Main conclusionsElephant distribution and abundance patterns have homogenized in response to increased space limitations, with group‐specific, fire‐driven distribution patterns emerging overtime. Results herein should be used to help manage elephant space‐use through the establishment of possible refuge areas and the development of more empirical research into elephant impacts in future.
Highlights
African Elephants (Loxodonta africana) are ecosystem engineers that alter and create habitats as they select for preferred resources in the landscape (Pringle, 2008; Ripple et al, 2015)
Using almost three decades of elephant population data, we investigate how the densities of bull versus herd groups respond to changes in various environmental conditions, namely rainfall, distance to major rivers and fire frequency
These specific covariates were se‐ lected because (a) rainfall has a well‐established relationship with vegetation productivity and habitat condition (Chamaille‐Jammes, Fritz, & Murindagomo, 2006; Richard & Poccard, 1998) that actu‐ ate ungulate dynamics in Africa (Ogutu, Piepho, Dublin, Bhola, & Reid, 2008); (b) distance to major rivers is an indicator of available surface water as well as landscape position and associated habitat gradient; (c) while fire frequency provides insight into the syner‐ gistic relationship between elephants and fire (Dublin, Sinclair, & McGlade, 1990; Shannon et al, 2011); (d) all data sets overlap with the census period, 1985–2012
Summary
African Elephants (Loxodonta africana) are ecosystem engineers that alter and create habitats as they select for preferred resources in the landscape (Pringle, 2008; Ripple et al, 2015). Using almost three decades of elephant population data, we investigate how the densities of bull versus herd groups respond to changes in various environmental conditions, namely rainfall, distance to major rivers and fire frequency These specific covariates were se‐ lected because (a) rainfall has a well‐established relationship with vegetation productivity and habitat condition (Chamaille‐Jammes, Fritz, & Murindagomo, 2006; Richard & Poccard, 1998) that actu‐ ate ungulate dynamics in Africa (Ogutu, Piepho, Dublin, Bhola, & Reid, 2008); (b) distance to major rivers is an indicator of available surface water as well as landscape position and associated habitat gradient; (c) while fire frequency provides insight into the syner‐ gistic relationship between elephants and fire (Dublin, Sinclair, & McGlade, 1990; Shannon et al, 2011); (d) all data sets overlap with the census period, 1985–2012. We investi‐ gated (a) the spatial processes (resource selection function) that govern the distribution of elephants, accounting for group‐type differences, while controlling for density increase over time; (b) significant changes to long‐term total elephant distribution and abundance patterns (regardless of group type) and; (c) significant changes to long‐term elephant group‐type distribution patterns (spatial probabilities of encountering bull vs. herd elephants in the landscape)
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