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FAUNAL DISTRICTS AND AREAS
All of the Sudan, from an overall zoogeographical standpoint, lies within the Ethiopian Faunal Region (Figure 1) except the desert wastes in the extreme northwestern corner that are included in the Palaearctic Faunal Region.
Faunal Districts, although based on a combination of factors, are mightily influenced in the Sudan by quantity and seasonal dis tribution of rainfall. The effect of rainfall is dramatically il lustrated as one travels from north to south by the gradual grada tion from extreme desert to African savannah with few trees and short grass in the north and more numerous trees and tall elephant grass in the south. Restricted patches of "jungle type" forest are encountered in western Equatoria, along the Congo watershed, and in the mountains of eastern Equatoria.
Except for a small component of the fauna that requires a cool climate combined with relatively high rainfall and is there fore confined to the highlands of eastern Equatoria, distribution of animal life in the Sud an is in general less modified by extremes of temperature than by rainfall. Those animals that do range into the Sudanese plains are per se adapted to high temperatures and within the Sudan their distribution is limited primarily by floral and rainfall factors. Before differences in temperature extremes can exert definitive influence the animal has succumbed to extremes of other factors.
The Faunal Districts of the Sudan and of the remainder of the Ethiopian Faunal Region (Figure 3), as delineated by Chapi (1932) for birds, nicely illustrate zoogeographical relation ships and differences on a continental basis. Disregarding the bulge of the Palaearctic Faunal Region into northeastern Sudan, a barren and almost entirely lifeless desert, the northernmost fringe of the country is part of the narrow Sudanese Arid Dis trict belt that extends across Africa from the Atlantic to the Red Sea. As readily realized from data concerning temperature (page 831), rainfall (page 834), and vegetation (page 837), the extremely sparse animal life that exists here is limited to the world's most highly adapted xerophilic species. Bordering this District to the south, the Sudanese Savannah District, extending from the Atlantic to the Ethiopien highlands, embraces most of
the vast plains of the Sudan. Here short to tall grasslands are dotted with scattered trees that are often thorny acacias and in southern latitudes include various broadleaf species. Although including much of West Africa beyond approximately 5°N.*, both of these Districts are faunistically an extension of the East and South African Subregion.
West African faunal elements in the Sudan are confined largely to Bahr El Ghazal Province, Equatoria Province west of the Nile, and isolated populations in and about the bases of mountain masses in eastern Equatoria Province. This faima, in the Ubangi-Uelle Savannah District, reaches southwestern Sudan from central Nigeria. Isolated from that of the more open sa vannahs of East African Districts, this fauna is composed of numerous genera, species, and subspecies not found in East Afri.
It is a peripheral, grassier extension of the West African (Guinean) Forest Districts that in the Sudan are represented by only a few limited forests in Equatoria Province.
In southern Sudan, Equatoria Province east of the Nile and southern Upper Nile Province support populations of animals typical of the East African Highland District. Open, grassy plains, with scattered thorn trees and with broad leaf trees around termite mounds and beside rivers, carry to its northern limit the magnificient plains fauna for which East Africa is famed. In general, these animals differ at least subspecifi cally from their relatives west of the Nile, although there is some interdigitation of East African elements into the western and northern Districts bordering the East African Highland.
Eastward, the effect of the Abyssinian Highland District is expressed in poorly explored outlying hills just within the Sud an frontier.
The Red Sea coast and the eastern slopes of the Red Sea Hills, by reason of higher relative humidity and more rainfall than surrounding areas, carry the fauna of the Somali Arid Dis. trict northward at least to Port Sudan.
*See modification of this latitudinal zonation for the Sudan, page 844.
As already stated, Chapin's outline of Faunal 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 study 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 Damer. 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.
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 determines 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
*Faunal Areas, as here used, are regional subdivisions of Faunal Districts that, in turn, 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.
addition to such extrinsic environmental factors as physical barriers, temperature, and humidity. For ectoparasites that com monly attack both wild and domestic animals a double set of values needs be employed.
The distribution of parasites that utilize widely differing hosts in each developmental stage is effected not only by the physiological range tolerable to the ectoparasite but also by that tolerated by the several types of hosts required to complete the life cycle. In families of insects consisting of many spe cies certain basic distributional patterns are more easily discerned than in the family Ixodidae composed of relatively few species variously adapted to a wide range of environments and hosts.
In Africa and in the Sudan in particular, where both domes tic animals and many wild animals make long migrations in search of water and grazing, particular caution should be exercised in geographic evaluation of collections consisting only of male ticks, which remain attached to the host for many months. Males may be unaccompanied by females, which generally feed for four to ten days, either because the reproductive season is not yet at hand or because they have been transported far beyond their normal range by hosts wandering in search of food and water. When outside their normal geographic range, these unassociated males are not only false zoogeographic indicators but of reduced epidemiological significance since they do not normally leave the host and attach to another. Inasmuch as domestic animal parasitizing ticks are frequently those also directly or indirectly associated with human diseases these considera tions assume additional importance.
The wide disparity in size and beauty between different species of ticks as well as in degree of exposure or conceal. ment of feeding sites on the host may give a false distribu. tional picture when collections are gathered haphazardly and by nonspecialists.
It goes without saying that in great areas of the world and especially in the Sudan, remoteness of considerable areas and lack of general and specialized interest by collectors may often result in skewed data or samplings that are far from homogenous.