Chimpanzee ( Pan troglodytes verus ) Density and Environmental Gradients at Their Biogeographical Range Edge
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Chimpanzee (Pan troglodytes verus) Density and Environmental Gradients at Their Biogeographical Range Edge Erin G. Wessling, et al. [full author details at the end of the article] Received: 29 November 2019 / Accepted: 29 September 2020/ # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Identifying ecological gradients at the range edge of a species is an essential step in revealing the underlying mechanisms and constraints that limit the species’ geographic range. We aimed to describe the patterns of variation in chimpanzee (Pan troglodytes verus) density and habitat characteristics perpendicular to the northern edge of their range and to investigate potential environmental mechanisms underlying chimpanzee distribution in a savanna–mosaic habitat. We estimated chimpanzee densities at six sites forming a 126-km latitudinal gradient at the biogeographical range edge of the western chimpanzee in the savanna–mosaic habitats of southeastern Senegal. To accompany these data, we used systematically placed vegetation plots to characterize the habitats at each site for habitat heterogeneity, tree density and size, and floral assemblages, among other variables. We found that both biotic and abiotic factors are potential determinants of the chimpanzee range limit in this ecoregion. Specifically, chimpanzee-occupied landscapes at the limit had smaller available floral assemblages less habitat heterogeneity, and contained fewer closed canopy habitats in which chimpanzees could seek refuge from high temperatures than in landscapes farther from the range limit. This pattern was accompanied by a decline in chimpanzee density with increasing proximity to the range limit. Our results provide several indications of the potential limits of food species diversity, thermal refuge, and water availability to the chimpanzee niche and the implications of these limits for chimpanzee biogeography, especially in the face of climate change predictions, as well as for species distributional modeling more generally. Keywords Ecography . Food availability . Habitat . Niche . Savanna–mosaic . Species
range limit . Thermoregulation
Handling Editor: Joanna Setchell Supplementary Information The online version contains supplementary material available at https://doi.org/ 10.1007/s10764-020-00182-3.
Wessling E.G. et al.
Introduction Abundant-center niche theory predicts that habitat suitability is highest at the center of a species’ range and decreases toward the outer boundaries of where that species is found (Brown 1984; Brown et al. 1995; Holt 2009; Hutchinson 1961). As habitat suitability decreases, species density likewise is expected to decrease, so that densities should be lowest at the range edge (Kawecki 2008; Sexton et al. 2009). Patterns of species density distributions can vary considerably depending on the limiting factors that dictate them. Accordingly, species densities may decline gradually across the range toward the edges or may remain stable across the range until they drop off at the very limits of
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