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Sudanese Faunal Areas Based on
A somewhat arbitrary, preliminary mapping of Faunistic Areas of tick distribution in the Sudan has been suggested (Figure 328, and pages 854 and 855). This scheme conforms as closely as permissable with that of Lewis (1953), which reflects the importance of critical and specialized factors of aquatic and semi aquatic breeding places of Tabanids as well as availability of hosts. Further study may reveal that additional divisions should be designated for ticks but the limits are not presently well understood. Lewis' Watershed, Marra, Nuba, Bome Gemi, (western) Floodplain, Sudd, and Gezira Areas are not charted for ticks since data are not yet sufficient to indicate the specialized character of tick fauna in these regions. The more intensive tick collections from southeastern Sudan, however, allow the specification that Lewis' Torit-Loelli Area may be separated into two distinct areas, the Torit Area and the Kapoeta Area. Inasmuch as Lewis' western sector of the Floodplain Area is abandoned for the present purposes, the eastern sector is referred to here as the Eastern Floodplain Area.
WEST AFRICAN SUBREGION
The RagaLoka Area, as here considered (Figure 328), is wider than that originally proposed by Chapin as the zone typical of West African fauna in the Sudan (Figure 1). It is a combination of Lewis' several southwestern Areas (Figure 327), the (Congo) Watershed, the Raga Loka, the (western) Flood plain, and the Sudd. Consisting of various types of forests and savannahs with more numerous trees than found elsewhere in the Sudan, this area largely lacks the broad grassy plains character of so much of the Sudan. Indicator tick species are those characteristic of the West African Subregion (page 852) though they represent only a small part of the total tick fauna ende mic in West Africa. As already stated, indicator species typical of the West African Subregion are exceptional in the Sud an outside of the Raga_Loka Area.
Forests and wooded savannahs of this area also shelter several species of the East and South African Subregion that are un known elsewhere in the Sudan. These are R. sulcatus, R. supertritus, R. tricuspis, and R. mihlensi. Restriction of these four ticks to this Area may indicate that they are characteristic of more humid and shaded East African areas than those found else. where in the Sudan and therefore they have survived only here. Each is a species of little known biology.
EAST AFRICAN SUBP.EGION
Data for this Area are more extensive than for any other in the Sudan. Commencing a few miles west of the Nile, which does not in itself appear to be an effective barrier, Torit Area is a vast, tree_dotted and clustered grassy plain that gradually becomes short grassy scrub east of Kapoeta. From its southern margin rise the various montane masses of limited extent that comprise the Imatone Area. To the north, the area becomes less densely wooded and numerous tick species vanish in the tall grass savannah. Few permanent streams break the plain but sev. eral extensive, poorly explored swamps fill depressions in the northern part of the Area.
Almost half of the tick species known from the Sudan have been collected in this Area. West African components are rare indeed owing primarily to the open forest or scattered tree as. pect of the plains and absence of extensive forests fringing streams. As already noted, such moderately xerophilic species as A. lepidum and R. pravus occur in the eastern sector of this Area but are considerably less common than in Kapoeta Area. Ticks requiring moderately cool temperatures and high humidity, such as R. appendiculatus, are absent here. Others that require moderate humidity, such as A. variegatum, are common here but their numbers are not so great as when the same species occur in restricted situations in the Raga Loka Area to the west.
IMAT ONG (MONTANE) AREA
The specialized tick fauna representative of both Subregions that is supported in these low, cool, partially forested moun tains is listed on page 850.
The montane masses consist of the horseshoe shaped Acholi. Imatong Mountains, the highest peak of which is Mount Kinyeti (10,456 feet elevation). To the east, the Dongotona Mountains that rise to 8605 feet elevation have an isolated northwesterly extension in the Lafit Hills. The more eastern Didinga Hills with Mount Lotuke the highest point at 9169 feet elevation, are carried to the northwest by the Boya Hills. The base of these mountains in the plains is at an approximate altitude of 2000 feet. The vertebrate and tick fauna of none of these montane masses is well known.
SUDANESE SAVANNAH DISTRICT
Kapoeta Area, an extension of Karamoja District of Uganda, is characterized by three important species that are common here but become less numerous westwards toward Torit, their western boundary in southern Sudan. These are R. pravus, A. cohaerens, and A. lepidum. Only the last named spēcies is known to extend northward into the Eastern Floodplain Area from where it fans out and becomes quite common in the Central Rainlands. A number of species present in adjacent Torit Area are not known from the Kapoeta Area. The more intensive work in the Torit Area may partially account for this disparity but the short grass scrub aspect of the eastern plains and the long and intense dry season are factors that may exclude many of these species. This is the area of vast migrations of tens of thousands of game animals from Upper Nile Province (Zaphiro 1949), a spectacular phenomenon that should be investigated for its significance in relation to tick distribution.
EASTERN FLOODPLAIN AREA
The picture of tick distribution in this area is character. ized by the presence of most of the widely ranging, common tropical species of the Sudan plains and by the apparent ab sence of numerous more specialized tropical species and north ern species. More extensive exploration is required before the true composition of the tick fauna of this Area can be evaluated.
CENTRAL RAINLANDS AREA
In the Central Rainlands, ticks of big game animals are ex ceedingly restricted or entirely absent. Few species typical of tropical East Africa that do range into this zone extend further north. Some populations of North African hyalommas penetrate this area though whether they are merely transported or actually reproduce here is uncertain. The presence of two Palaearctic species is intriguing. H. marginatum may be established here from nymphs introduced by migrating birds but this explanation cannot be applied to the single host tick H. detritum. The north ern limit of this Area is probably the most critical and definite of any boundary in the Sudanese plains save those of the few montane masses that rise from these plains. H. impressum is found only in this and parts of the adjacent Area to the north.
The Nuba Mountains should be considered as a separate sector of this area but data on tick distribution are not yet sufficient ly definitive to allow designation of these mountains as a dis tinct faunal Area.
Here the desert aspect emerges. Further research will prob ably show that this area may be divided into a southern sector in which rare, small populations of several tropical African tick species survive and a northern sector inhabited only by xerophilic species. The narrow Nile Valley carries a small number of spe cies northwards to its great bend, beyond which only H. 1. leachii is established. Various hyalommas, R. s. sanguineus, and o. savignyi are the indicator species of this Area in which few others are known to be established. Palaearctic components are here a strong feature, especially in the north. Like the Nuba Mountains in the Central Rainlands, the Marra Mountains may prove to be a distinct faunal Area after sufficient data have been obtained from this region.
No tick records are available from these harsh deserts al though rare populations of argasids and hyalommas are suspected to occur in restricted localities.