This species occupies a fairly restricted geographical distribution in moist, warm, tropical areas along the eastern escarpment from northern Tanzania to southern Malawi (Josso and Prevost 2000), although its extent of occurrence exceeds 400,000 km2. The type locality of the species and one subspecies is at the extreme northern limits of its range at Taveta, just over the Tanzanian border in southern Kenya (Josso and Prevost 2000). This subspecies has been recorded predominantly on the north east coast and on isolated mountain blocks along the mountains of the Eastern Arc and southern rift in Tanzania. The other subspecies (D. thomsoni malawiensis) is centred on highland blocks in Malawi (Josso and Prevost 2000). Some of the patchiness is probably an artefact of forest fragmentation. However, taking the reduction of forest cover within the species' habitat mosaic into account (WWF Wildfinder 2012), the area of occupancy has been estimated as approximately 7,500 km2.
Habitat and Ecology
Available data suggest that this species is restricted to forest patches or patches of dense woodland as several published collection records are from forest reserves (Josso and Prevost 2000). Furthermore, it has been trapped to pig dung in surviving forest patches on the finer-grained soils of the East Usambara (Usambaa) mountains (W. Newmark & R.B.M. Senzota unpubl. data).
The distribution of this species primarily coincides with ecoregions that include forest habitats, comprising the Northern Zanzibar-Inhambane coastal forest mosaic (AT0125), Eastern Arc forests (AT0109), Southern Rift montane forest-grassland mosaic (AT1015), and South Malawi montane forest-grassland mosaic (AT1014) (Olson et al. 2001).
Some environmental characteristics for 64 combined locality records are as follows: altitude: mean: 724 Â± 451 (S.D.), range: 0.6-1,559 m; annual rainfall: mean: 1,089 Â± 307 (S.D.), range: 545-1,588 mm; annual temperature: mean: 22.8 Â± 2.5 (S.D.), range: 17.5-26.5oC (max. + min. / 2).
IUCN Red List Assessment
Red List Category
Red List Criteria
For the present, Diastellopalpus thomsoni has been listed as Least Concern. Although relatively range-restricted, it still has a fairly extensive extent of occurrence and an area of occupancy outside the thresholds for threatened categories under criterion B. However, human population pressure is high across the entire range of this species, particularly at the lower altitudes where most collections were made. Firewood collection and clearance of forest for agriculture are common threats across all four ecoregions that constitute the main range of the species. Forest cover has, thus, been lost across the species range. Quantifying forest cover loss and the time period of losses may lead to an inferred estimate of population reduction and a change to the listing of the species under criterion A.
Human population pressure is high across the entire range of this species, particularly at lower altitudes where most collections were made. According to historical reports, the type locality of Taveta was once densely wooded although open savanna now dominates in the area. Firewood collection and clearance of forest for agriculture are common threats across all four ecoregions that constitute the main range of the species.
The range of this species now comprises a patchwork of forest fragments and agricultural lands. In Tanzania, there is little protection of most forests within national parks or reserves in the entire coastal region, Eastern Arc, or southern rift ecoregions. However, in Malawi, most surviving forest patches result from government protection. Conservation of forest is a necessity for the survival of this species.