Spatial Statistics to Quantify Patterns of Herd Dispersion in a Savanna Herbivore Community

Understanding the spatial distribution of species is a fundamental issue in ecology, yet quantitative descriptions of animal species' distributions are rare. In this chapter, we use a spatialstatistics approach to describe the spatial distribution of herds of large herbivores in Laikipia, central Kenya. We used Global Positioning System technology and spatial point pattern analysis (F-, G- and J-functions) to characterise herd distributions of the 9 most abundant species comprising large herbivore communities in African savannas. F-function analysis is based on estimating the probability of a herd occurring within radius r of randomly selected focal points. G-function analysis is similar, but based on randomly selected focal herds. The J-function is derived from the ratio of G- and F-functions. Comparing results from the different functions was instructive about possible causes of spatial patterning at the landscape level. All species displayed consistently aggregated distributions under F- and J-function analyses, partly because wildlife has been displaced by humans and livestock from sections of the study area. By contrast, the G-function provides a description of dispersion under more natural conditions because areas lacking herds are excluded from the analysis. G-function results showed 5 species to display random or nearly random dispersion patterns (zebra, impala, Grant's gazelle, eland and hartebeest), while the remainder were aggregated (African elephant, giraffe, African buffalo and Thomson's gazelle).