Scorpions of the Brandberg Massif, Namibia: Species Richness Inversely Correlated with Altitude

ABSTRACT A previous list of scorpions from the Brandberg Massif and vicinity, north-western Namibia (Omaruru District. Erongo Region), is updated, based on a survey of the Massif and surrounding areas (the region delimited by 21°00′S–21°30′S and 14°00′–15°00′E) conducted during three separate expeditions, and augmented by an examination of material in museum collections. More than 1000 specimens, representing more than 100 point-locality records, were examined for the study. Notes on the ecology and distribution of the scorpions on the Massif and surrounding areas are provided. Excluding one dubious record, 20 scorpion species in seven genera (Brandbergia, Lisposoma, Hottentotta, Parabuthus, Uroplectes, Hadogenes, and Opistophthalmus) of four families (Bothriuridae, Buthidae, Liochelidae, Scorpionidae) are recorded from the area, which presently has the richest scorpion fauna in Namibia, if not southern Africa, and ranks among those with the richest scorpion faunas in the world. The high diversity of scorpions on the Brandberg Massif and vicinity is attributed to the heterogeneity of landforms, substrata and habitats in the area. The scorpions of the Massif and surrounding areas may be classified into seven ecomorphotypes, using every available niche. The species richness of the scorpion fauna is inversely correlated with altitude. The greatest diversity of genera and species occurs at the base of the Massif and in the surrounding areas, and decreases towards the summit. Five species occur in the area surrounding the Massif but not at its base, five at its base (below 500 m) but not on its slopes, two on its lower slopes (500–1000 m), but not on its middle slope (1000–1500 m), upper slope (1500–2000 m) or summit (above 2000 m), and two on its summit, upper and middle slopes only. Only five species occur from the base to the summit of the Massif.


INTRODUCTION
Namibia presently has the highest species richness and endemism of scorpions in southern Africa (Prendini 2000a(Prendini , 2005a. All four families, eight (62 %) genera, and 63 (45 %) species of southern African scorpions occur in the country, of which two (15 %) genera and at least 31 (22 %) species are endemic (Lamoral 1979;Prendini 2000aPrendini , b, 2001aPrendini , 2003aPrendini , 2005a. It could be argued that this is nothing more than a reflection of the fact that the scorpion fauna of Namibia is better studied than that of other southern African countries, as a result of the extensive collections and publications on Namibian scorpions by various specialists (notably A. Harington, B.H. Lamoral, R.F. Lawrence, G. Newlands and the first author). Indeed, the species richness and endemism of scorpions in South Africa appears to be even greater than that of Namibia, based on work in preparation by the first author on several speciose genera, especially Hadogenes Kraepelin, 1894, Opistophthalmus C.L. Koch, 1837and Uroplectes Peters, 1861. Nevertheless, despite decades of research on the scorpions of Namibia, new species and even genera continue to be discovered within its borders (Prendini 2000a(Prendini , b, 2003a(Prendini , b, 2005aHarington 2002), partly due to the rugged and inhospitable desert terrain and partly due to the cryptic nature of most desert scorpion species that inhabit it. Many, for example, are fossorial and can only be collected by means of ultraviolet (UV) light detection (Honetschlager 1965;Stahnke 1972;Sissom et al. 1990), pitfall trapping or, in the case of Opistophthalmus, burrow excavation. Some of the most recently described Namibian scorpions are endemic to the Brandberg Massif and vicinity , in the Omaruru District (Erongo Region) of north-western Namibia (Prendini 2000a(Prendini , 2003a. Prendini (2000a) recorded fourteen scorpion species, in five genera and three families, from the area. The subsequent description of Brandbergia haringtoni Prendini, 2003 and the discovery of new records of Lisposoma elegans Lawrence, 1928 from the Massif (Prendini 2003c) increased the total to sixteen species, in seven genera and four families. A further five species are recorded in the present study: Hadogenes hahni (Peters, 1862); Opistophthalmus coetzeei Lamoral, 1979; Opistophthalmus gibbericauda Lamoral, 1979; Parabuthus kraepelini Werner, 1902; Uroplectes gracilior Hewitt, 1913. However, the single record of O. coetzeei is questionable. The presence of Parabuthus stridulus Hewitt, 1913 was not confirmed within the study area, although it has been collected further west at the Ugab River mouth (Lamoral 1979). Excluding the dubious record of O. coetzeei, twenty scorpion species in seven genera and four families have been recorded, to date, from the Brandberg Massif and vicinity (Table 1).

STUDY AREA
The study area comprises the region delimited by 21°00'S-21°30'S and 14°00'E-15°00'E, an area representing two half-degree squares and approximately 2300 km 2 , in the Omaruru District (Erongo Region) of north-western Namibia. The dominant landform within the study area is the prominent, circular Brandberg Massif, rising abruptly from the surrounding gravel plains of the central Namib Desert (Figs 1, 3), and covering an area of ca 650 km 2 (Marais & Kirk-Spriggs 2000). An extensive central plateau occurs at an altitude of about 2000 m (Fig. 8), from which many peaks arise, the highest of these being Königstein (2573 m), the highest point in Namibia. Deep alluvial valleys and ravines, leading down to the surrounding pediplain, radially dissect the steep slopes of the periphery (Figs 4, 7). At the higher altitudes , orographic amelioration of the prevailing hyperarid conditions around the base and lower slopes (Figs 1-5; Olszewski 2000) provide a refugium for relict fauna (Irish 1994;Craven & Craven 2000;Marais & Kirk-Spriggs 2000;Prendini 2003a). Besides the Brandberg Massif, other prominent landforms falling within the study area are the Goboboseberge, the Messum Crater, the Messum River, the Uis Mountains and numerous smaller inselbergs (Figs 2,7).
Three separate expeditions to the area were conducted in January 1998, December 2003 and April 2006. The first expedition surveyed the base of the Brandberg Massif, including several major gorges intersecting its periphery, and surrounding areas (Figs  1-4). The two subsequent trips, each of which involved a hike from the base along the Goaseb (Ga-Asab or Ga-Aseb) Gorge, surveyed its slopes and summit . During these trips, collections were made at periodic intervals along a transect from the base to the summit during two different seasons (hot, dry and warm, wet).

MATERIAL AND METHODS
Specimens collected during the three expeditions were mostly found at night using UV light detection (Honetschlager 1965;Stahnke 1972;Sissom et al. 1990). A portable UV lamp, comprising two mercury-vapour tubes attached to a chromium parabolic reflector and powered by a rechargeable 7 Amp/hr, 12 V battery, was used for this purpose. Additional specimens were collected during the day by turning stones and excavating burrows. A portable Garmin™ GPS V device was used for recording the geographical coordinates of collection localities in the field.  Lawrence, 1928 La X X X X X X

Family Scorpionidae
Opistophthalmus carinatus (Peters, 1861) P e X X X X X X

Opistophthalmus lamorali
In addition to the material that was newly collected for the survey, an attempt was made to examine all available specimens in museum collections, originating from localities within the study area. Abbreviations for collections in which material is deposited, are as follows: Albany Museum, Grahamstown, South Africa (AMGS); American Museum of Natural History, New York (AMNH), some bearing accession numbers from the Alexis Harington Collection ( More than 1000 specimens, representing more than 100 point-locality records, were examined for the study. Only a small proportion of the locality records from museum collections were accompanied by geographical coordinates or quarter-degree squares, usually entered by the collector or subsequently added by the curator or collections manager. These were checked for accuracy and an attempt was made to georeference as many of the other locality records as possible, by reference to gazetteers and the official 1:50 000 topo-cadastral maps of Namibia published by the Government Printer. Retrospectively georeferenced locality records and other supplementary locality data are provided in square brackets in the Material Examined. The classification followed in this contribution is that of Prendini and Wheeler (2005 Ecology and distribution: This endemic Namibian species is known only from two female specimens taken at a single, indefinite locality in the upper slopes (1650 m) of the Goaseb (Ga-Asab or Ga-Aseb) Gorge, just below the summit on the southern side of the Massif (Figs 6, 7). Two attempts to collect additional specimens at similar altitude in the upper reaches of the Goaseb Gorge (December 2003 andApril 2006) were unsuccessful. It is likely that this species is restricted to the summit, upper and middle slopes of the Massif, where the rainfall is greater than at lower altitude. Based on its morphology, B. haringtoni is probably lapidicolous, sheltering under stones (Prendini , 2003a. Lawrence, 1928 Lisposoma elegans : Lawrence 1928: 281-286, pl Ecology and distribution: This lapidicolous species shelters under stones (Lamoral 1979;Prendini , 2003c. Although it may also occur in Angola, this species has been recorded only from Namibia (Lamoral 1979;Prendini , 2003cPrendini , 2005a. It has been collected from the base (Fig. 4) to the summit (Fig. 8) of the Brandberg and in rocky areas surrounding the Massif. Fet et al. (2004) and Soleglad et al. (2005) reported one specimen from Königstein (2573 m), the highest peak on the Massif.

Parabuthus kraepelini
Parabuthus villosus (Peters, 1862)   Ecology and distribution: This semi-lithophilous species (Fig. 14) excavates shallow burrows or scrapes under stones in consolidated sandy, gritty or clayey substrata (Lamoral 1979;Prendini , 2004. Although it may also occur in Angola, this species has been recorded only from Namibia and South Africa (Lamoral 1979;Prendini 2004Prendini , 2005a. It has been collected in rocky areas surrounding the Brandberg and in gorges intersecting the Massif (Fig. 4), e.g. Numaskloof (470 m), but not on the slopes or the summit. Hewitt, 1913 Uroplectes carinatus gracilior : Hewitt 1913: 147-148 (part Ecology and distribution: This lapidicolous species (Fig. 15) shelters under stones and in grass tussocks (Lamoral 1979;) on rocky outcrops and gravel plains in areas surrounding the Brandberg (Fig. 1) and adjacent landforms (e.g. the Messum Crater). Although it may also occur in Angola, this species has been recorded only from Namibia and South Africa (Lamoral 1979;Prendini 2005a).

Uroplectes gracilior
Uroplectes otjimbinguensis (Karsch, 1879)   Ecology and distribution: This corticolous species shelters under the peeling bark of trees or in holes in tree trunks (Lamoral 1979;. It is endemic to Angola and Namibia (Lamoral 1979;Prendini 2005a) and has been collected from the base (Fig. 4) to the summit (Fig. 8) of the Brandberg and also in the areas surrounding the Massif.
Hadogenes angolensis Lourenço, 1999: 932-936, figs 1-17, 19, 20, 23, 25,  Ecology and distribution: This lithophilous species shelters in the cracks and crevices, and under the exfoliating flakes, of weathered rock outcrops and under stones resting on bedrock (Lamoral 1979;. It is endemic to Angola and Namibia (Lamoral 1979;Prendini 2005a, b) and has been collected in areas to the southeast of the Brandberg, but not on the Massif itself.
Opistophthalmus coetzeei Lamoral, 1979Opisthophthalmus coetzeei: Lamoral 1979. Ecology and distribution: This pelophilous species excavates shallow to moderate, spiral burrows in open ground or at the base of small stones in consolidated gritty to loamy substrata (Lamoral 1979;). This species is endemic to Namibia (Lamoral 1979;Prendini 2005a). Its occurrence on the Brandberg is doubtful. It is possible, but unlikely, that the species occurs on the gravel plains surrounding the Brandberg. The next closest record for the species is on Farm Vrede 119 in the Karibib District, further southeast at 21°27.96'S:15°08.64'E (SMN 1938). Lamoral, 1979Opisthophthalmus gibbericauda: Lamoral 1979 Ecology and distribution: This semi-psammophilous species excavates moderate to deep, spiral burrows in open ground in consolidated sandy-loam substrata (Lamoral 1979;. It is endemic to Angola and Namibia (Lamoral 1979;Prendini 2005a) and has been collected in areas to the southeast of the Brandberg, but not on the Massif itself.
Ecology and distribution: This psammophilous species excavates deep, spiral burrows in semi-consolidated sandy or gritty substrata (Lamoral 1979;) on sandy to gravel plains (Fig. 2) or dry riverbeds intersecting the Brandberg (e.g. Numaskloof), around the base of the Massif and in the surrounding areas. It occurs in Angola, Botswana, Namibia, South Africa, Zambia and Zimbabwe (Lamoral 1979;Prendini 2005a).

RESULTS AND DISCUSSION
Based on the current survey, twenty scorpion species in seven genera and four families are recorded from the Brandberg Massif and vicinity (Table 1), which presently has the richest scorpion fauna in Namibia, if not southern Africa. The only other regions of comparable scorpion diversity in southern Africa are the Soutpansberg and vicinity in the Limpopo Province (Soutpansberg District) of South Africa, with 19 species in eight genera and three families recorded, and the Koa River Valley and associated mountain ranges near Aggeneys in the Northern Cape Province (Namaqualand District) of South Africa, with 17 species in five genera and three families recorded (L. Prendini, unpubl. data). These areas rank among those with the richest scorpion faunas in the world, comparable to the most diverse areas in the Baja California Peninsula, Mexico (Williams 1980;Polis 1990).
The high diversity of scorpions on the Brandberg Massif and vicinity, like that of other areas with a high diversity of scorpions, is attributable to the heterogeneity of landforms, substrata and habitats in the area Figs 1-8). The scorpions of the Brandberg Massif and surrounding areas may be classified into seven ecomorphotypes (Table 1), including five substratum generalists, four lapidicolous and one corticolous species, and 15 substratum-specialists, spanning the extent of the substratum-hardness continuum : three psammophilous, five semi-psammophilous, one pelophilous, three semi-lithophilous, and three lithophilous species. The diversity of ecomorphotypes represented by the scorpion species of the Brandberg Massif and surrounding areas has enabled them to exploit every available niche. The species richness of the scorpion fauna of the Brandberg Massif and surrounding areas is inversely correlated with altitude (Fig. 21). The greatest diversity of genera (6) and species (20) occurs at the base of the Massif (below 500 m) and in the surrounding areas (Table 1; Figs 1-4), where the heterogeneity of landforms, substrata and habitats is greatest, and decreases towards the summit (Fig. 8). Five species, including two psammophiles, occur in the area surrounding the Massif, but not at its base: P. gracilis, P. kraepelini, P. namibensis, U. gracilior, H. hahni, O. gibbericauda, O. jenseni. Five species that also occur in the area surrounding the Massif, including one psammophile, occur at its base but not on its slopes: P. granulatus, P. villosus, O. lamorali, O. wahlbergii. Unsurprisingly, no psammophilous species occur on the Massif itself; the fauna of the Massif is dominated by lithophilous, semi-lithophilous and lapidicolous species. Two species that also occur in the area surrounding the Massif and at its base, occur on its lower slopes (500-1000 m; Fig. 5), but not on its middle slope (1000-1500 m), upper slope (1500-2000 m; Fig. 6) or summit (above 2000 m; Fig. 8 Only five species, all of which also occur in the area surrounding the Massif, occur from its base to its summit: L. elegans, P. brevimanus, U. otjimbinguensis, U. planimanus, H. tityrus.