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The Historic Ranges of Three Equid Species in North-East Africa: A Quantitative Comparison of Environmental Tolerances
I. E. Bauer, J. McMorrow and D. W. Yalden
Journal of Biogeography
Vol. 21, No. 2 (Mar., 1994), pp. 169-182
Published by: Wiley
Stable URL: http://www.jstor.org/stable/2845470
Page Count: 14
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The historic ranges of three equid species native to north-east Africa are analysed with respect to annual rainfall, several temperature parameters and a satellite-derived multispectral index of primary productivity. Equus africanus Fitzinger, Equus grevyi Oustalet and Equus burchelli Gray used to largely replace each other, geographically, with narrow zones of range overlap occurring between E. africanus and E. grevyi in the Awash valley, and between E. grevyi and E. burchelli in southern Ethiopia and northern Kenya. The three species are shown to succeed each other along an environmental gradient. The position of each species on this gradient and the resulting location and extent of its range are discussed. Competitive exclusion, specific adaptations and historic events are likely determinants of equid distribution. In the area of sympatry between E. grevyi and E. burchelli, mixed habitat characters as well as environmental fluctuations seem to prevent either species from excluding the other. Different social organizations of E. grevyi and E. burchelli and the resulting migratory patterns may be adaptations to the environment in their allopatric ranges; in their sympatric range they could alleviate competition.
Journal of Biogeography © 1994 Wiley