RODENTS OF LIBYA 43 



quercinus denticulatus is confined to the Fezzan. Such a discontinuous 

 distribution for members of the same species is not in agreement with 

 modern evolutionary concepts. Mayr (1931) has proposed the term 

 semispecies for such widely separated allopatric members of the 

 same species which normally differ so strikingly in morphological 

 characters that reproductive isolation can almost be assumed. If 

 one subscribes to Mayr's classification, all of the dormice of Libya, 

 which are presently recognized as subspecies of a single species, 

 Eliomys quercinus, would be regarded as morphologically distinct 

 semispecies of a single, monophyletic superspecies. 



The subspecies Gerbillus gerbillus aeruginosus, Gerbillus campestris 

 patrizii, Jaculus deserti vastus, and Jaculus jaculus cufrensis also 

 represent geographic isolates, but their ranges are located well within 

 the limits of the ranges of their respective species, rather than on the 

 periphery of the species range as in the above examples. Three of these 

 subspecies occur only in the isolated oases of Cufra and Bzema in 

 southern Oyrenaica, and Jaculus deserti vastus is known only from the 

 Gebel el Harug el Asued of central Libya. All of these subspecies 

 represent geographically isolated populations which are physically 

 and genetically isolated from neighboring populations. As a result of 

 this isolation, genetic exchange with neighboring populations is 

 impossible. Thus, these populations have been subjected to a rapid 

 repatterning of their gene pools with consequent reduction of vari- 

 ability and an increase in the rates of morphological differentiation 

 and genetic fixation. Those subspecies restricted to Cufra Oasis are 

 generally smaller in body and cranial size than other representatives 

 of their respective species and, in this respect, represent a stage in 

 clinal variation. Jaculus deserti vastus is significantly larger in body 

 size than other representatives of this species in Libya. These rodent 

 popidations in Cufra and the Gebel el Harug el Asued illustrate 

 clearly the significance of geographic isolation in the evolutionary 

 process. 



In summary, habitat segregation could have led to the splitting 

 of the gene pool of parental species with subsequent development of 

 other biological and behavioral differences. Spatial isolation of these 

 populations has tended to further increase these differences, resulting 

 originally from ecological (or habitat) isolation. 



The populational structure of Libyan rodents is characterized by 

 two primary structural components: geographically isolated popula- 

 tions and, less frequently, a series of contiguous populations that 

 show progressive changes in morphological characters (clines). In 

 some cases, where the ranges of two subspecies meet, there are zones 

 of intergradation containing individuals intermediate in morphological 

 characters. 



