Nama Karoo Research Articles

Classification and ordination of plant communities of the Naukluft Mountains, Namibia

Abstract. To determine the relationship between vegetation and environmental parameters in a desert‐savanna ecotone, vegetation in the Naukluft Mountains of Namibia (southern Africa) was described and analysed in terms of environmental parameters determining the observed patterns. 12 plant communities, largely characterized by low shrubs, were described on the basis of a classification. Through ordination altitude, clay, potassium content of the substrate and, to a lesser extent, habitats were identified as underlying environmental factors determining the composition of these plant communities. The edaphic parameters showed some correlation with subsurface geology, but microclimatic conditions, water availability and level of disturbance appeared to override the effect of nutrient composition provided by different substrate.Communities of conservation importance, such as plant communities composed of Karoo shrubs, are prevalent on the mountain plateau, presenting an isolated outpost of Nama Karoo vegetation. The transitional status between desert and savanna, remnant patches of Nama Karoo and the high habitat diversity mark the importance of this high altitude area for biodiversity conservation.

The Karoo: ecological patterns and processes

Foreword P. W. Roux Preface Acknowledgements Part I. The Driving Variables W. Dean and S. Milton: 1. The climate of the Karoo - a functional approach P. Desmet and R. Cowling 2. Soils of the arid south-western zone of Africa M. Watkeys 3. Paleoenvironments M. Meadows and M. Watkeys 4. Plant biogeography, endemism and diversity R. Cowling and C. Hilton-Taylor 5. Biogeography, endemism and diversity of animals C. Vernon Part II. Form and Function B. Lovegrove: 6. Form and function in perennial plants G. Midgley and F. van der Heyden 7. Functional aspects of annual and biennial plants M. van Rooyen 8. Plant reproductive ecology K. Esler 9. Animal form and function B. Lovegrove 10. Animal foraging and food W. Dean and S. Milton Part III. Dynamics P. Novellie: 11. Population-level dynamics S. Milton, R. Davies and G. Kerley 12. Community patterns and dynamics A. Palmer, P. Novellie and J. Lloyd 13. Modelling populations and community dynamics in Karoo ecosystems K. Kellner and J. Booysen 14. Spatially explicit computer simulation models - tools for understanding vegetation dynamics and supporting rangeland management F. Jeltsch, T. Wiegand and C. Wissel Part IV. Human Impacts W. Siegfried: 15. Hunters and herders in the Karoo landscape A. Smith 16. Historical and contemporary land use and the desertification of the Karoo M. Hoffman, B. Cousins, T. Meyer, A. Petersen and H. Hendricks 17. Alien plant invaders of the Karoo: attributes, impacts and control S. Milton, H. Zimmerman and J. Hoffman 18. Comparison of ecosystem processes in the Nama Karoo and other deserts W. Whitford 18. The Succulent Karoo in a global context: plant structural and functional concepts comparison with North American winter rainfall deserts K. Esler, P. Rundel and R. Cowling 20. The Karoo: past and present S. Milton and W. Dean References Index.

Rainfall as a breeding stimulus and clutch size determinant in South African arid‐zone birds

Rainfall is known to be a stimulus for initiating breeding in arid‐zone birds, but its influence on clutch size is unknown for most southern African birds. The breeding activity of nine out of 11 species studied in the arid Nama Karoo biome of South Africa increased markedly after appreciable rainfall. Some resident insectivores did breed in the absence of rainfall, even under drought conditions, but also laid eggs within one week of small rain showers. Nomadic granivores required more substantial rainfall to stimulate what was usually a synchronized, population‐wide breeding response. The timing and length of the breeding season was dependent on the integrated effect that rainfall and temperature had on the growing season of the vegetation. Over 50% of the 11 species studied showed evidence of an increase in clutch size following large rainfall events. Grey‐backed Finchlark Eremopterix verticalis began laying larger clutches within one week of a rainfall stimulus, illustrating how rapid this response can be.

A New Rhadamanthus Species (Hyacinthaceae) from the Northwestern Cape, South Africa

Rhadamanthus involutus is a rare, hysteranthous-leaved species from the Bokkeveld Escarpment, west of Nieuwoudtville, Northern Cape Province, South Africa. Most closely related to R. albiflorus B. Nordenstam, R. involutus is distinguished by apically recurved outer tepals that are conspicuously spotted with green at the base, and suberect inner tepals that have involute margins which overlap to form a tube. The bulbs grow on exposed sandstone sheets between patches of dry fynbos and flower in midsummer. Rhadamanthus Salisbury is a small, poorly understood genus of Hyacinthaceae that is endemic to southern Africa. Nordenstam (1970) and Obermeyer (1980) recognized 11 species, mostly from semi-arid habitats in the Nama Karoo, Succulent Karoo, and Fynbos biomes (see Rutherford, 1997). The genus is distinguished from its close ally, Urginea Steinheil, solely by its derived anther dehiscence. Unlike the unspecialized, longitudinally dehiscent anthers of Urginea, the anthers in Rhadamanthus dehisce either apically, or if by longitudinal slits then these are initiated from the apex and extend below the midline but never reach the base of the thecae. Despite this variation, dehiscence in Rhadamanthus is never complete and the anther opening always remains somewhat pore-like, having its greatest width near the top of the anther (Nordenstam, 1970). Although subtle, Nordenstam (1970) chose to maintain this distinction, awaiting the resolution of the difficult and complex relationships between the remaining genera in tribe Scilleae (sensu Hutchinson, 1959). Jessop (1977) supported this view in his re-evaluation of Drimia Jacquin ex Willdenow, Urginea, and related genera. Plants of Rhadamanthus are easily overlooked in the field. The leaves are consistently hysteranthous, the flowers are inconspicuous, and the bulbs flower during the unfavorable summer drought. Thus the geographic records of many Rhadamanthus species in Nordenstam's (1970) treatment of the genus are regarded as incomplete, and the fruit and seeds of several species still remain unknown. Rhadamanthus involutus was first discovered in 1993 in flower in sparse, dry fynbos on the Bokkeveld Escarpment west of Nieuwoudtville, northwestern Cape. The flowers differ uniquely in the form, disposition, and markings of the outer and inner tepals. The tepals are unequal and biseriate, with the outer whorl distinctly overlapping the inner whorl at the base. The outer tepals recurve apically at anthesis and each bears a distinctive, basal, olive green spot. In contrast the inner tepals are unmarked, suberect, and involute so that each has a tapering tubular form. The non-nodding flowers are also unusual in the genus. Anther dehiscence in R. involutus is tardy and incomplete, and the longitudinal slits which proceed from the apex of the thecae do not extend to the base. Obermeyer (1980) recognized four other species of Rhadamanthus (R. fasciatus B. Nordenstam, R. albflorus B. Nordenstam, R. namibensis Obermeyer, and R. karooicus Obermeyer) with this type of anther dehiscence and described subgenus Rhadamanthopsis Obermeyer to accommodate them. Rhadamanthus involutus is the fifth known species of this subgenus. Although its affinities in the genus are not well understood, R. involutus has white flowers and extremely short filaments relative to the anthers. These characters also occur in R. albiflorus and suggest an alliance with this southwestern Cape species. Field observations on the bees (family Anthophoridae) that visit the flowers of R. involutus indicate that the anther dehiscence in Rhadamanthus is associated with pollination by bee vibration. Additional characters that Rhadamanthus species share with other known buzz-pollinated taxa (ErNovoN 9: 111-113. 1999. This content downloaded from 157.55.39.217 on Mon, 18 Apr 2016 07:25:36 UTC All use subject to http://about.jstor.org/terms

A New Species, Notes on Subgeneric Taxa, and New Synonyms in Hessea (Amaryllidaceae: Amaryllideae) from South Africa

Hessea tenuipedicellata, a new graniteloving species from Namaqualand, shares slender, pliant, upwardly curved pedicels, white flowers, and channeled, narrow, tepals with H. stenosiphon (Snijman) D. & U. Muiller-Doblies. Hessea subg. Hessea is amplified to include H. tenuipedicellata and H. stenosiphon, and H. subg. Kamiesbergia (Snijman) Snijman is a new synonym of H. subg. Hessea. In H. subg. Namaquanula (D. & U. MuillerDoblies) Snijman, Namaquanula etesionamibensis D. & U. MUiller-Doblies is a new synonym of Hessea bruce-bayeri (D. & U. Muiller-Doblies) Snijman. Hessea Herbert, a genus of small autumn-flowering plants, is endemic to the winter and autumnrainfall regions of the Nama Karoo, Succulent Karoo, and Fynbos biomes in southern Africa. Cladistic analysis of tribe Amaryllideae using morphological data showed that Hessea resolves within subtribe Amaryllidinae in a terminal clade that includes its actinomorphic-flowered allies, Strumaria Jacquin and Carpolyza Salisbury. The subtribe is recognized by filaments that are connate at the base but are secondarily free in Carpolyza and some species of Strumaria; by seeds that have chlorophyll in the integument; and by stomata on the testa (Snijman & Linder, 1996). Other representatives of the subtribe that are basal to Hessea, Strumaria, and Carpolyza are Amaryllis L., which has unique pink to white seeds, Nerine Herbert, Brunsvigia Heister, and Crossyne Salisbury. Hessea sensu Snijman (1994) is divided into three subgenera that share derived floral characters. The perigone in Hessea is actinomorphic, and this ultimately turns brown and remains open with age, unlike the perigone that becomes deeply pigmented and finally collapses in all other actinomorphic-flowered Amaryllidinae.

Alien plant assemblages near roads in arid and semi‐arid South Africa

SummaryHerbaceous and woody alien plants visible from a moving vehicle were recorded along 1 km roadside transects at 5 km intervals over a distance of 5869 km in the semi‐arid and arid Fynbos, Succulent Karoo, Nama Karoo and Arid Savanna (Kalahari) biomes in South Africa. Each 1 km transect was classified by biome and vegetation type, mean annual rainfall, rainfall seasonality, soil surface type and landuse adjoining the roadside. Although travelling speed affected the range and frequency of plant species observed, the method was repeatable at a speed of 100 km h−1. Alien plants occurred in 98% of 119 Fynbos, 81% of 204 Succulent Karoo, 72% of 661 Nama Karoo, 47% of 171 Arid Savanna and 100% of seventeen Grassland transects. Alien species richness per site was correlated with mean annual rainfall, but in all regions, sites adjacent to cultivation had significantly more alien species than sites adjoining rangeland. The alien plant assemblage of the arid winter‐rainfall Succulent Karoo included species from mesic winter‐rainfall lowland Fynbos and the arid Nama Karoo receives unseasonal rainfall. The frequencies of Prosopis spp., Atriplex spp. and Opuntia ficus‐indica were not significantly greater near cultivation, and these perennial plants, all of which are dispersed by indigenous and domestic animals, can invade natural rangeland in arid and semi‐arid southern Africa.

Predation on the tent tortoisePsammobates tentorius: a whodunit with the honey badgerMellivora capensisas prime suspect

The collection of 63 shells of the tent tortoise Psammobates tentorius in the Bushmanland Nama Karoo revealed that 49% of them had been cleanly broken open and the body of the tortoise removed. The...

The distribution and biology of nomadic birds in the Karoo, South Africa

Dryland nomadic bird species, as a proportion of all bird species in a biome in southern Africa, are highest in the arid grassland and arid and semi‐arid Karoo in South Africa. Nomadic birds, of which the most widespread species is the greybacked finchlark Eremopterix verticalis (Smith), are most frequently observed in the north‐central and north western Nama Karoo. The species richness of nomadic species is inversely correlated with species richness of all bird species in the Karoo. Since the distribution of nomadic birds is in areas where rainfall is patchy, low (<250 mm per year) and aseasonal, this supports the idea that fewer species are able to cope with resources that are patchy in time and space, and that there has been selection for nomadism in the species that are able to use patchy environments. Species richness and abundance of nomadic birds is negatively correlated with rainfall amount but positively correlated with the coefficient of variation of the rainfall and with rainfall in autumn. The frequency of nomadic birds is inversely correlated with altitude range; nomadic species are most often recorded in structurally simple habitats (shrubland and grassland) on open plains. Most nomadic bird species in the Karoo are granivorous. Perennial desert grasses are important components of the habitat and diet of small nomadic granivores, and also provide nest sites and nest material. Nomadic birds can breed throughout the year, without a clearly defined ‘season’ in both the Succulent and Nama Karoo. Average clutch sizes do not differ significantly between resident and all nomadic species in the arid and semi‐arid Karoo. Nomadism is an evolutionary stable strategy for individual species only when extremes in environmental conditions are frequent enough, and unpredictable enough, to maintain movements to high resource patches or to maintain dispersal away from low resource patches. If high rainfall years are too regular or infrequent, or peaks in fluctuations of resources in the environment too low, or rainfall patches are randomly distributed, nomadism would not be maintained as part of the individual behaviour pattern.

THE ABUNDANCE AND MOVEMENTS OF LUDWIG'S BUSTARD NEOTIS LUDWIGII

Summary Allan, D.G. 1994. The abundance and movements of Ludwig's Bustard Neotis ludwigii. Ostrich 65: 95–105. An analysis of bird-atlas data, road counts, an aerial census, and landowners' comments confirmed that Ludwig's Bustard Neotis ludwigii is a winter migrant to the winter-rainfall Succulent Karoo biome. In addition, the species appears to migrate seasonally between the Namib and Namibian Escarpment regions. There is no evidence, however, that the abundance of the species decreases in the summer-rainfall Nama Karoo biome during the winter. There was a Significant positive correlation between Ludwig's Bustard densities, as measured during road counts, and the total rainfall in the three months before each count, but this explained relatively little of the variation in Ludwig's Bustard densities. The total population size of the species was estimated at between 56 000 and 81000 individuals.

A preliminary survey of the aculeate wasps and the bees of the lower reaches of the Nossob River Valley, Kalahari Gemsbok National Park, South Africa

An annotated list of aculeate wasps and of bees collected during a preliminary survey of these insects in the lower reaches of the Nossob River Valley, Kalahari Gemsbok National Park is presented. Flowers visisted, and notes on provision and nest type are given. Meloid beetles collected on the flowers are listed. The species composition and geographical affinities of the community of aculeate wasps and of bees in relation to those of four sites in the Karoo Biome (in Namaqualand, in the southern Great Karoo, in the Little Karoo and in the easternmost extension of the Nama Karoo) are discussed briefly.

AN ECOLOGICAL PERSPECTIVE OF LARK (ALAUDIDAE) DISTRIBUTION AND DIVERSITY IN THE SOUTHWEST-ARID ZONE OF AFRICA

Summary Dean, W. R. J. & Hockey, P. A. R. 1989. An ecological perspective of lark (Alaudidae) distribution and diversity in the southwest-arid zone of Africa. Ostrich 60:27-34. The southwest-arid zone of Africa comprises the Succulent, Karoo, Nama Karoo and Desert. The region Has a wide diversity of climate, land form, soils and vegetation. Most of the southwest-arid zone receives less than 250 mm mean annual rainfall. The larks are well presented in the southwest-arid zone and 19 species occur in this region. On the basis of movement patterns, the arid-zone larksMaybe divided into resident (n = 9) and nomadic (n = 8) species. The residents are characterized by their larger body size, mainly insectivorous diets and limited movements: these species occur in pairs or small groups, Mayhold territories throughout the year and are characteristic of the southern and southwestern Karoo. The nomads are smaller, predominantly granivorous, and occur frequently in very large groups which make extensive movements. These species are characteristic of the northern and northwestern Karoo. The larksMayalso be differentiated on the basis of colour match with soil type, with “grey” species predominating in the southern Karoo, and “red” species in the Nama Karoo and on Kalahari Sands.

Apple by-products as stock foods

The Hantam-Tanqua-Roggeveld subregion is situated in an area where the Fynbos, Succulent Karoo and Nama Karoo biomes meet. Life form spectra were compiled at a species richness and vegetation cover level in order to determine the affinities of the vegetation of the subregion with respect to its Succulent Karoo, Fynbos and Nama Karoo Biome status. A percentage succulence was also calculated for both species richness and cover. Comparisons of life form spectra and succulence were made across the eight vegetation associations found in the area and across three broad vegetation groups, i.e., Mountain Renosterveld, Winter Rainfall Karoo and Tanqua Karoo. Mountain Renosterveld vegetation was characterised by high chamaephyte, cryptophyte and therophyte species contributions. Compared to the other broad vegetation groups, the Mountain Renosterveld group showed phanerophyte contributions at the vegetation cover level to be highest, but the degree of succulence was low. Winter Rainfall Karoo vegetation was co-dominated by high levels of chamaephyte, cryptophyte and therophyte species with chamaephytes dominating the vegetation cover. Succulent contributions to species richness and cover values were higher than for Mountain Renosterveld vegetation. Tanqua Karoo vegetation was dominated by chamaephyte species or co-dominated by chamaephyte and cryptophyte species with therophyte species contributions lowest of all vegetation groups. Contributions by succulent species to richness and vegetation cover were high in the Tanqua Karoo. Life form spectra of the Mountain Renosterveld associations compared poorly to other sites in the Fynbos Biome. However, the low level of succulence in the Mountain Renosterveld associations also precludes its inclusion into the Succulent Karoo Biome. The large contribution of succulent species at a species and vegetation cover level in Winter Rainfall Karoo and Tanqua Karoo associations confirms that these two groups belong to the Succulent Karoo Biome. Affinities to the Nama Karoo Biome were indicated by the low level of succulence at a vegetation cover level in one of the Winter Rainfall Karoo associations (Roggeveld Karoo).