The response of elephants to the spatial heterogeneity of vegetation in a Southern African agricultural landscape Research article Received: 04 February 2003 Accepted: 10 September 2004 Abstract
Based on the agricultural landscape of the Sebungwe in Zimbabwe, we investigated whether and how the spatial distribution of the African elephant (
Loxodonta africana) responded to spatial heterogeneity of vegetation cover based on data of the early 1980s and early 1990s. We also investigated whether and how elephant distribution responded to changes in spatial heterogeneity between the early 1980s and early 1990s. Vegetation cover was estimated from a normalised difference vegetation index (NDVI). Spatial heterogeneity was estimated from a new approach based on the intensity (i.e., the maximum variance exhibited when a spatially distributed landscape property such as vegetation cover is measured with a successively increasing window size or scale) and dominant scale (i.e., the scale or window size at which the intensity is displayed). We used a variogram to quantify the dominant scale (i.e., range) and intensity (i.e., sill) of NDVI based congruent windows (i.e., 3.84 km × 3.84 km in a 61 km × 61 km landscape). The results indicated that elephants consistently responded to the dominant scale of spatial heterogeneity in a unimodal fashion with the peak elephant presence occurring in environments with dominant scales of spatial heterogeneity of around 457–734 m. Both the intensity and dominant scale of spatial heterogeneity predicted 65 and 68% of the variance in elephant presence in the early 1980s and in the early 1990s respectively. Also, changes in the intensity and dominant scale of spatial heterogeneity predicted 61% of the variance in the change in elephant distribution. The results imply that management decisions must take into consideration the influence of the levels of spatial heterogeneity on elephants in order to ensure elephant persistence in agricultural landscapes. Keywords African elephant Dominant scale Intensity NDVI Spatial heterogeneity Windowed variogram References Adler, P.B., Raff, D.A., Lauenroth, W.K. 2001 The effect of grazing on the spatial heterogeneity of vegetation Oecologia 128 465 474 Google Scholar Birky, A.K. 2001 NDVI and a simple model of deciduous forest seasonal dynamics Ecological Modelling 143 43 58 Google Scholar Burton, M. 1999 An assessment of alternative methods of estimating the effect of the ivory trade ban on poaching effort Ecological Economics 30 93 106 Google Scholar Cohen, W.B., Spies, T.A., Bradshaw, G.A. 1990 Semivariograms of digital imagery for analysis of conifer canopy structure Remote Sensors Environment 34 167 178 Google Scholar Cumming, D.H.M. 1981 The management of elephant and other large mammals in Zimbabwe Jewel, P.A. Holt, S. Hart, D. eds. In problems in Management of Locally Abundant Wild Animals Academic Press Inc. New York 91 118 Google Scholar
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