Southwestern South Africa Research Articles

<i>Eremiolirion</i>, a new genus of southern African Tecophilaeaceae, and taxonomic notes on <i>Cyanell</i>a alba

The generic affiliation of Cyanella amboensis Schinz has been uncertain since the species was excluded from the genus Cyanella L. in 1991. The species has two leaves, a divaricately branching inflorescence, ebracteolate pedicels, and acti- nomorphic flowers with monomorphic anthers. It is endemic to the western parts of central and northern Namibia. Other species of Cyanella have several leaves, racemose inflorescences, bracteolate pedicels, zygomorphic flowers with dimor­phic anthers, and are endemic or near-endemic to the winter rainfall region in southwestern South Africa and southern Namibia. These differences are consistent with the recognition of the species as a distinct genus within the family. Phylogenetic analysis of plastid DNA sequences indicates that C. amboensis Schinz is sister to the other species of Cyanella, a relationship that also supports its independent generic status. The monotvpic genus Eremiolirion is according­ly erected to accommodate the species. Minor differences in flower colour and vegetative morphology in Cyanella alba L.f. are shown to correlate with the three disjunct groups of populations in which the species occurs, and these populations are recognized at the level of subspecies.

Black Harrier Circus maurus of the Fynbos biome, South Africa: a threatened specialist or an adaptable survivor?

Black Harrier Circus maurus is a rare southern African endemic that may have lost over 50% of its core breeding habitat in the last century as a result of extensive land transformation by agriculture, invasive alien vegetation and urbanization in the Fynbos biome. We partially surveyed both the western (Swartland) and southern (Overberg) coastal plains of south-western South Africa, over 3 years (2000–2002) for breeding Black Harriers, and found a distinctly polarized distribution. Nests were concentrated either along the coastal strip or inland in montane habitats, and generally absent from heavily cultivated and transformed inland plains areas. Limited evidence (direct observations, prey remains) suggests that harriers forage in cereal croplands but generally do not breed in these modified environments. We recorded breeding success at nests in coastal (Dune Thicket) and montane (Mountain Fynbos) habitats. Harriers bred successfully along the coast and nests were aggregated in loose colonies around wetlands. Harriers in montane environments bred poorly, took a wide range of prey, and were subject to high levels of nest predation. We propose that Black Harriers have been displaced from lowland Renosterveld and Fynbos habitats (characterized by better foraging and nesting opportunities), primarily by the advent and spread of cereal agriculture. The conservation and future research implications of this hypothesis are discussed.

A mixed-feeding Equus species from the middle pleistocene of South Africa

The dietary regime of Equus capensis from the Middle Pleistocene of South Africa is investigated by mesowear analysis. Results indicate that the mesowear signature of this species resembles that of two extant mixed feeders, the Grant's Gazelle (Gazella granti) and the Thomson's Gazelle (Gazella thomsoni), suggesting a mixed feeding dietary strategy for E. capensis. The mesowear signature of a contemporaneous population of Equus mosbachensis from Europe (Arago, France) is also determined for comparative purposes and has a typical grazing signature. In general, all extant species of Equus are believed to be almost exclusively grazers. However, a considerable degree of dietary flexibility is recently reported. The dietary signal of E. capensis is considered to be the result of feeding on the unique fynbos vegetation, which was beginning to establish itself at this time in southwestern South Africa. Grasses are a minor component of this floral kingdom. Our findings thus provide further evidence for the unexpected flexibility in feeding strategies of Equus, the most widely distributed equid taxon in the Quaternary. They highlight the potential use of the attrition"abrasion wear equilibrium as a habitat indicator, by mirroring the availability of food items in mammalian herbivore ecosystems.

Rare earth element behavior in soils and salt pan sediments of a semi-arid granitic terrain in the Western Cape, South Africa

The rare earth element (REE) contents of soils and pan sediments of the Darling Hills granitic terrain of southwestern South Africa were determined to study the behavior of REE during weathering in a semi-arid, Mediterranean climate. The P-rich, S-type bedrock granite has a middle REE (MREE) enrichment relative to post-Archean Australian sedimentary rocks (PAAS) that primarily reflects the REE content of feldspar and accessory apatite. Initial chemical weathering of the granite results in the loss of REE, particularly Ce, Eu and the heavy REE (HREE). The enrichment of REE in soils relative to bedrock granite corresponds to clay mineral and amorphous Fe oxide content in the case of the light REE (LREE) and precipitation of pedogenic calcite in the case of the HREE. Quartz sand dilutes the REE content, and concentration of K-feldspar produces positive Eu anomalies. Cerium is rapidly precipitated during weathering and retained in clayey, upper soil horizons as insoluble CeO 2. Most pan sediments have a bowl-shaped REE pattern that is derived from the accumulation of eroded catchment soils modified by precipitation of evaporative carbonates. REE enrichment, particularly LREE, and the large negative Ce anomaly of oxidized basal pan sediment relative to the bedrock granite suggest that REE entering the pan by groundwater flow are sorbed onto amorphous Fe oxides. In contrast, goethite-rich nodules from the pan have a low REE content and show HREE enrichment relative to the granite. Precipitation of pedogenic calcite and evaporative pan carbonates greatly increases the retention of the HREE in these semi-arid soils. Diagenetic pan dolomite has a REE pattern similar to pedogenic and evaporative calcite, but with a significantly lower REE content. The REE patterns indicate that, although most abundant in the bedrock granite, the MREE are least retained by soils during weathering. The LREE are generally retained by clayey and amorphous Fe-oxide-rich soils and sediments, whereas HREE are retained by precipitation of soil and pan carbonates.

ENSO‐like decadal variability and South African rainfall

Decadal to multidecadal ‘ENSO‐like’ SST and circulation patterns in joint EOFs of global SST and MSLP, may be linked to South African rainfall variability. For eastern/northern South Africa (summer rainfall), the average of the 9–13 year and 18–39 year bandpass filtered EOFs tracks the rainfall well for 1903–1998. Higher (lower) pressure, warmer (cooler) SST in the Pacific and Indian Oceans and offshore (onshore) winds characterise the positive (negative) EOF signal and decreased (increased) rain. For southwestern South Africa (winter rainfall), the average of the 13–18 and 18–39 year filtered EOFs tracks the rainfall well from 1903–1982 with the 9–13 year EOF working better from 1983–1998. The suggested mechanism involves shifts in the upper level jet and in the strength of the subtropical high pressure belt and circumpolar trough.

Space-time diversification of Androcymbium Willd. (Colchicaceae) in western South Africa

We examined patterns of cpDNA RFLP variability using 21 restriction endonucleases in 21 populations of Androcymbium that represent 12 endemic species distributed in the winter rainfall areas of South Africa to explore the diversification of the genus in its area of maximum species diversity. Our results are supportive of a diversification landscape characterized by continued opportunistic short-range invasion, naturalization, and rapid speciation, in which the selective action of the different environments where Androcymbium species occur determined their colonization success and subsequent short-range geographic expansion. The historical presence of fire, the constraint imposed by the low concentration of nutrients throughout southwestern South Africa and the different reproductive capabilities of Androcymbium species have also likely stimulated species' diversification. Our divergence time estimates bolster the view that speciation of South African Androcymbium initiated in the late Eocene, intensified in the Oligocene and proceeded more sporadically during the Miocene. These chronological estimates also substantiate the previous hypothesis that most lineages of Androcymbium in South Africa are much more ancient than their North African relatives, whose diversification began in the late Miocene-early Pliocene.

UPb SHRIMP and SmNd age constraints on the timing and sources of the Pan-African Cape Granite Suite, South Africa

Geochemical and isotopic UPb SHRIMP and SmNd studies in three granitic plutons from the Pan-African Neoproterozoic/Cambrian Saldania Mobile Belt, southwestern South Africa supports differences in the sources and timing of emplacement of the main plutons related to the Cape Granite Suite as established by previous researchers. The Phase I, early syn-tectonic Darling Batholith Granitoid reflects an overall peraluminous chemical signature compatible with derivation mainly from melts extracted from paraderived crustal sources (Sa1 association). The Phase II, late to post-tectonic Robertson Pluton, reflects affinities to the Australian l-type granites (1a association). Despite the good structural constraints on the syn- and post-tectonic origin, the UPb ages point to a broadly synchronous crystallisation episode at 547±6 Ma and 536±5 Ma, respectively. In addition to UPb, Nd isotopic studies were also carried out for both plutons, as well as for the Riviera Granite, another phase II (1a association) pluton. The initial ε Nd (550 Ma) based on a depleted mantle model range from −3.5 (Darling), to −3.1 (Robertson) and to −2.6 (Riviera). The Nd mean crustal residence ages are 1559 Ma for Darling, 1626 Ma for Robertson and 1243 Ma for Riviera. Despite the small databank, a dominant Mesoproterozoic (∼ 1600 Ma) crust may be seen as the best candidate to explain the model T DM ages obtained. All the data largely overlap with others recently obtained for other plutons within the Cape Granite Suite and cast doubts on the current correlation between Saldania and the southeastern Brazilian, Dom Feliciano Belts.

Streams in Mediterranean Climate Regions: Abiotic Influences and Biotic Responses to Predictable Seasonal Events

▪ Abstract Streams in mediterranean-climate regions (areas surrounding the Mediterranean Sea, parts of western North America, parts of west and south Australia, southwestern South Africa and parts of central Chile) are physically, chemically, and biologically shaped by sequential, predictable, seasonal events of flooding and drying over an annual cycle. Correspondingly, aquatic communities undergo a yearly cycle whereby abiotic (environmental) controls that dominate during floods are reduced when the discharge declines, which is also a time when biotic controls (e.g. predation, competition) can become important. As the dry season progresses, habitat conditions become harsher; environmental pressures may again become the more important regulators of stream populations and community structure. In contrast to the synchronous input of autumn litterfall in forested temperate streams, riparian input to mediterranean-type streams is more protracted, with fall and possibly spring peaks occurring in streams in the Northern Hemisphere and a summer peak existing in their Southern Hemisphere counterparts. We present 25 testable hypotheses that relate to the influence of the stream hydrograph on faunal richness, abundance, and diversity; species coexistence; seasonal changes in the relative importance of abiotic and biotic controls on the biotic structure; riparian inputs and the relative importance of heterotrophy compared to autotrophy; and the impact of human activities on these seasonally water-stressed streams. Population increases in mediterranean-climate regions (particularly in fertile regions) result in an intensification of the competition for water among different users; consequently, water abstraction, flow regulation, increased salinity, and pollution severely limit the ability of the streams to survive as sustainable, self-regulated systems.

Where, why, and to what extent have rangelands in the Karoo, South Africa, desertified

We used simple questionnaire surveys to obtain rough categorical information on the status of semiarid and arid rangelands in the Karoo, South Africa. We sent questionnaires to extension officers of the Department of Agricultural Development, asking them to rank the condition of the rangeland in their extension districts (usually about 500 farms) on a three- or five-point scale. The questionnaire also sought information on the possible reasons for changes in the condition of the rangelands; vegetation types most at risk on mismanaged rangelands; and changes in the status of plants, birds, and mammals. Extension officers rated 35% of the semiarid rangelands in southwestern South Africa (the Karoo and southern Kalahari Desert) as being in poor condition. There was some congruency between the perceived condition of the agricultural extension district and the percentage that the stocking rate had decreased. Rangeland condition in more arid areas tends to be poor. Stocking rates have decreased disproportionately more in arid areas than in the more mesic areas of southwestern South Africa. Grasses were rated as the most threatened group of plants, and succulents the least threatened group. Overgrazing in the past was considered to be the most important cause of present-day rangeland condition, followed by present overstocking of rangelands. Antelope were considered more threatened by rangeland management than mammalian carnivores. Avian raptors and bustards, gamebirds, and tortoises were all perceived to be threatened by rangeland mismanagement.

Convergence and non‐convergence of plant traits in climatically and edaphically matched sites in Mediterranean Australia and South Africa

Abstract This paper compares the occurrence of plant traits in five edaphically matched sites at the Barrens, southwestern Australia and the Agulhas Plain, southwestern South Africa. The two regions are very closely matched in terms of their Mediterranean‐type climates, landforms, soil types and disturbance regimes. On both continents, matched sites on all substrata (siliceous sand, quartzite, laterite, limestone and calcareous sand) support sclerophyllous shrublands with a similar mix of growth forms. Soils from all substrata in both Australia and South Africa are extremely nutrient‐poor except for the calcareous sands where high levels of phosphorus were recorded. Contrary to expectations, Australian soils are not generally less fertile than their South African counterparts. The frequency of species in different leaf consistence categories was similar on the two continents, as was the leaf specific mass of overstorey shrubs from all substrata. Woody plants with leaf spines are significantly more frequent on Australian nutrient‐poor substrata. Among woody plants, species with canopy‐stored seed are significantly more frequent on Australian nutrient‐poor sites, whereas species with bird‐dispersed fruits and inter‐fire germination are significantly more frequent on South African limestone and calcareous sand. There was good evidence for convergence between the two continents in the frequency of other seed biological traits. The study indicates strong convergence between Australian and South African shrublands in the frequency of a wide range of traits relating to plant form and function. Examples of non‐convergence are probably due to regional and historical processes rather than differences in the contemporary physical environments of the two study areas.

Mechanisms for enhancing nutrient uptake in plants, with particular reference to mediterranean South Africa and Western Australia

The major constraints to nutrient uptake by vascular plants in mediterranean South Africa and Western Australia are: very infertile soils, relatively low temperatures when water availability is high, and hot, dry summers. These constraints are partly overcome through increased efficiency of uptake, tapping novel sources of nutrients, and prolonging water uptake. Absorptive area per unit “cost” may be enlarged directly through increased fineness of the root system and proliferation of long root hairs. This reaches its greatest development in the root clusters of the Proteaceae (proteoid roots), Restionaceae (“capillaroid” roots) and Cyperaceae (dauciform roots). Absorptive area is increased indirectly through fungal hyphae which extend from hairless rootlets into the soil. Two major groups can be recognised: general (VA mycorrhizas) and host-specific (ericoid, orchid and sheathing mycorrhizas). Mycorrhizas are the most widespread specialised modes of nutrition and are probably universal in such major taxa here asPodocarpus, Acacia, Fabaceae, Poaceae, Asteraceae, Rutaceae, terrestrial orchids, Ericales and Myrtaceae. General mycorrhizas are the least drought-adapted of mechanisms for maximising absorptive area. All have been implicated in enhancing P uptake through increasing access to inorganic P, solubilisation and shortening the diffusion path. However, selective uptake of other nutrients, especially N, by host-specific mycorrhizas may be equally important. Included under novel sources of nutrients are free N2 (utilised by N2-fixing nodules), small-animal prey (carnivorous leaves) and persistent leaf bases (aerial roots ofKingia australis). Both legume and non-legume N2-fixing species are well-represented in these two regions, with stands of individual species in southwestern Australia estimated to contribute 2–19 kg N/ha/yr to the ecosystem. Free nitrogen fixation requires additional nutrients, especially Mo and Co, but is enhanced following fires and by supplementary uptake mechanisms, especially VA mycorrhizas. Southwestern Australia is particularly rich in carnivorous species. Nitrogen, P, K and S are important nutrients absorbed, with digestion aided by enzymes provided by bacteria and the glands. Parasitic plants both tap novel sources of nutrients and capitalise on any efficient water and nutrient uptake mechanisms of the hosts. Root parasites are better represented than stem parasites in mediterranean South Africa and Western Australia. Phosphorus and K in particular are absorbed preferentially by the haustoria, but much remains to be known about their modes of operation. Maximum activity of all uptake mechanisms, except those attached to some deep-rooted plants, is restricted to winter-spring. Most new seasons’s rootlets and specialised roots are confined to the uppermost 15 cm of soil, especially in or near the decomposing litter zone. Nutrient uptake is further enhanced by the tendency for the rootlets to cluster, trapping water by capillary action and prolonging nutrient release. As an early product of decomposition, N tends to be available as NH4 (rather than NO3) and it is absorbed preferentially by almost all specialised modes of nutrition. Microorganisms are required in the formation and/or functioning of all these structures, except haustoria. Uptake mechanisms which are optional to the plant reach their peak contribution to the root system at soil nutrient levels well below those required for greatest plant growth, when they may be absent altogether. It is only over the narrow range of nutrient availability, where shoot content of a nutrient is greater in the presence of the mechanism than in its absence (other factors remaining constant), that specialised modes can be termed nutrient-uptake “strategies.” For all specialised modes of nutrition, the component genera are better represented in these two regions than in the surrounding more fertile, arid to subtropical regions of much greater area. Endemism of species with each mode exceeds that for the two floras overall (75%). This is taken as preliminary evidence that specialised modes of nutrition are best represented in nutrient-poor soils. While they serve to limit nutrient loss from the ecosystem, their proliferation is therefore not necessarily a response to increasing “leaks” in the system. A hierarchical scheme of the functional/structural relationships between the various mechanisms is presented, starting with the rootless, VA-mycorrhizal plant as the most primitive condition. Taxa with many of the specialised modes of nutrition at present in southwestern South Africa and Western Australia have been evident in the pollen record since the early Tertiary Period. The absence of ectomycorrhizal forests in mediterranean South Africa, in marked contrast to Western Australia, can be traced to differences in their paleohistory. In both regions, the combination of fluctuating, but essentially diminishing, nutrient and water availability that began with the first mediterranean climate < 5 million years ago resulted in decimation of the less-tolerant rainforest ancestors on the one hand, and remarkable rates of speciation of the pre-adapted sclerophyll nucleus on the other.