Page images
PDF
[merged small][graphic]

All of the Sudan, from an overall zoggeographical 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 grade. 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 Sudan is in general less modified by ex. tremes of temperature than by rainfall. Those animals that do range into the Sudanese plains are r se adapted to high temper. atures and within the Sudan their dis ribution is limited pri_ marily 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)has delineated by Chapin (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 alost entirely lifeless desert, the northernmost fringe of the country is part of the narrow Sudanese Arid District 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 Ethiopian highlands, embraces most of

the vast plains of the Sudan. Here short to tall grasslands are dotted with scattered trees that are often thorny acaoias 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 fauna, 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 Africa. 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 soe 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 Sudan 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 District northward at least to Port Sudan.

[graphic]

*See modification of this latitudinal zonation for the Sudan, page 81,4.

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.

[merged small][graphic][merged small]

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

[graphic]

*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 bar. riers, temperature, and humidity. For ectoparasites that conu unnly 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 dis.

~cerned 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 re. duced epidemiological significance since they do not normally leave the host and attach to another. Inasmch as domestic animal parasitizing ticks are frequently those also directly or indirectly associated with human disehses 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 concealment 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.

Tick species having marked host predilections may occupy the same geographic area as the favorite host or only a certain segment of the host range; for example, H. hou i appears to be present in most areas where its favorite host, %ne ground squirrel Euxerus erythropus, occurs. On the other hand, the elephant para... site I. tholloni 1S not known from the northern and southern peri. phery-of its host's range, the Varanus lizard parasite A. exorna._ tum does not follow its host into and areas, and such hyrax parasites as H. be uaerti and its related species occur in only a restricted area 0 e host's range.

Distributional data for most argasid species of the world are extremely sparse due to the specialized and laborious techniques necessary for collecting them. Even such a commonplace species as that presently considered to be 0. moubata, long believed to be well understood geographically, is now confused by a mounting body of biological evidence that tends to discredit or at least to modify critically earlier impressions but is yet too limited to be definitive.

The number and variety of hosts an individual species utilizes throughout its life cycle profoundly effects its distri.. bution and density. A single host tick such as B. decoloratus that feeds on easily available herds or groups of antelopes and cattle is spared many of the dangers resulting from being for_ saken as a newly hatched larva or a newly molted nymph or adult in an inhospitable environment where it must seek an entirely different type of host for survival. It may thus become locally numerous and also be carried afar by both wild and domestic hosts under conditions frequently favorable for survival and reproduc_ tion. Similarly, a species that utilizes the same type of host for all developmental stages, even though it releases and re. attaches two or three times, has advantages over one that cannot survive unless a certain variety of hosts for nourishing the different stages are present.

The frequency with which immature stages of several African amblyommas attack birds probably accounts in part for their relatively wide distribution and population density. In semiarid climes of North Africa and the Near East, where small mammals are rare or localized, the great predilection of immature hyalcrnzuas

« PreviousContinue »