As already stated, Chapin's outline of Faimal Districts is 

 a most functional one for generalized faunistic concepts. Be- 

 fore turning to the relation of ticks to these Faunal Districts 

 it is useful to consider briefly the only stvidy devoted to Faunal 

 Areas* of the Sudan, that of Lewis (1953) based on the distribu- 

 tion of Tabanids (Figure 327). In Lewis' map, the combination 

 of the Raga-Loka Areas with the eastern Flood Plain Area and 

 the Sudd Area collectively form a unit equivalent to though 

 slightly wider than Chapin^s Ubangi-Uelle District. Lewis' 

 Beja Area, on the Red Sea coast and extending as a narrow in- 

 land strip to Kassala, is a slightly extended version of that 

 part of Chapin's Somali Arid District that reaches into the 

 Sudan. The division of Chapin's Sudanese Savannah District 

 into a Central Rainlands Area in the south and a Fasher-Butana 

 Area in the north reflects the effects on animal distribution 

 of increasing aridity from south to north. Chapin's Sudanese 

 Arid District is modified by Lewis' eastward restriction of 

 the Baiyuda Area to exclude the plains south of El Darner. These 

 discriminations, resulting from Lewis' vast experience with in- 

 sects of medical importance in the Sudan, considerably assist 

 the evaluation of data for distribution of ticks in this country''. 



TICK DISTRIBUTION 



Introduction 



Prior to analysis of the Sudanese tick fauna distributional- 

 ly, it might serve a useful purpose to analyze briefly a few of 

 the specialized criteria that must be applied to ectoparasites 

 and especially to ticks. 



A complex variety of factors limits the geographic range 

 of any animal and deternines the optimal and marginal environ- 

 ments in which populations may thrive or simply survive. For 

 ectoparasites in general a number of apparent and obscure in- 

 trinsic host-ectoparasite relationships must be considered in 



*Fatinal Areas, as here used, are regional subdivisions of Faunal 

 Districts that, in tvirn, are regional subdivisions of the two 

 Subregions of the Ethiopian Faunal Region, i.e. the West African 

 Subregion and the East and South African Subregion. 



- 8Ai^ _ 



