RODENTS OF LIBYA 233 



plain between the Mediterranean Sea and the coastal escarpment and 

 the transitional desert farther inland. 



The Sand Sea of Rebianna serves as an effective barrier to gene flow 

 between jerboas inhabiting the oases of Cufra and Tazerbo, and the 

 Sand Sea of Calanscio prevents contact between these populations 

 and those of the nominate subspecies to the north. Genetic interchange 

 between animals from Gialo and those of coastal Libya is of doubtful 

 occurrence owing to extensive sandy plains and dunes interposed 

 between their ranges. Some genetic exchange occurs between coastal 

 and interior populations in the region of the oases of Socna, Hun and 

 Uaddan, but generally, the Fezzanese jerboas have maintained their 

 genetic integrity. In northern Tripolitania, the coastal escarpment 

 effectively separates the jerboas of the coastal plain from those of the 

 "high deserts" of the interior. 



Ecological observations. Jaculus jaculus inhabits both the 

 littoral deserts and the interior oases of Libya. On the coastal plain 

 they are common in the sandy hummocks and large coastal dunes, and 

 farther inland are confined to the sandy margins of the oases where 

 vegetation occurs sparingly for several kilometers beyond the palm 

 groves of the oasis proper. This peripheral vegetation, composed of 

 Calligonum, Tamarix, and thorny perennials, is interspersed with 

 barren areas of sandy, rock-strewn plains. Large, solitary hummocks 

 are present in these outlying areas and provide suitable sites for 

 burrow construction above the water table. 



Occasionally, jerboas are taken from sandy areas at the bases of date 

 palms and tamarix in the interior of the oasis and occur here with 

 Gerbillus gerbillus, Gerbillus pyramidum, and Gerbillus amoenus. 



They are of rare occurrence in rocky deserts and playas far removed 

 from oases. In these latter areas, J. jaculus is supplanted by the 

 darker colored Jaculus deserti. These two species are known to occur 

 sympatrically along a narrow zone of contact on the inner margins of 

 the coastal plain and probably occur together in other parts of Libya. 



Jerboas normally begin foraging shortly after dusk, but when 

 cold temperatures prevail, they emerge from their burrows later in 

 the night. In Libya, prolonged periods of cold are uncommon, hence 

 it is doubtful if jerboas hibernate there. In a few instances, jerboas 

 were taken when temperatures fell below 30° F. 



Jerboas are difficult to catch by standard trapping methods, and 

 accordingly trap yield is usually low, thus rendering an incorrect 

 estimate of population size. Jerboas are probably more abundant in 

 Libya than trapping success would indicate. 



The pale, ochraceous color of these jerboas is undoubtedly an 

 adaptive response to the prevailing color of the soil on and in which 

 they live. Jaculus jaculus is markedly paler in dorsal color than J. 

 deserti, which inhabits the grayish brown soils of the hamadas. 



285-134 O — 68 16 



