. Biology of the Heteromyidae. Heteromyidae. 670 MARES. Fig. 24.—Xeric scrubland of the Sahara Desert in Wadi Natroun, Egypt. (Photo: M. A. Mares) 1968), more than the rest of the world's deserts combined. It is among the hottest and driest of deserts and contains a great diversity of habitats, including extensive dune areas, mountain ranges, wadis and other areas of topographic relief and sub- strate diversity (Ayyad and Ghabbour, 1986; Grenot, 1974; Le Houerou, 1986; Monod, 1986). The Sahara is arid at its northern limits, extremely arid in the central por- tions, and semiarid at the souther
. Biology of the Heteromyidae. Heteromyidae. 670 MARES. Fig. 24.—Xeric scrubland of the Sahara Desert in Wadi Natroun, Egypt. (Photo: M. A. Mares) 1968), more than the rest of the world's deserts combined. It is among the hottest and driest of deserts and contains a great diversity of habitats, including extensive dune areas, mountain ranges, wadis and other areas of topographic relief and sub- strate diversity (Ayyad and Ghabbour, 1986; Grenot, 1974; Le Houerou, 1986; Monod, 1986). The Sahara is arid at its northern limits, extremely arid in the central por- tions, and semiarid at the southern limits. In its most arid portions, Grenot (1974:104) noted that "One can sometimes travel for 400-500 km without seeing anything but sand, gravel, or slabs of ; In such areas the desert is ". .. devoid of a drop of water or a sprig of ; It might be expected that in such an arid and extensive desert natural selection would have acted in such a manner that a high degree of desert ad- aptation would be favored among the reg- ular inhabitants of the desert, and this is indeed the case. The Sahara has a long history of aridity, although its present great expanse may be more recent than previously thought. Like subtropical deserts elsewhere, part of the reason that the Sahara is arid is its position astride the 30° latitudinal band, where de- scending dry air causes arid zones around the world if other climatic and geologic fac- tors do not mitigate this aridity (Logan, 1968). Thus, some portions of the globe have probably always been drier than other por- tions, although not necessarily desertic (Ax- elrod, 1950, 1972). Originally, a portion of the Sahara formed one of two major Afro- Asian arid areas in the Early Tertiary (Wal- ter et al., 1983), with a portion of the Gobi Desert being the second (below). However, much evidence supports the idea that the extent of the Saharan arid zone was much less pronounced in the last several thousand years a
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