Marburg, University, Diss., 2004. / Enth. 6 Sonderabdr. aus verschiedenen Zeitschr.

Würzburg, University, Diss., 2001.

Kalaharituber pfeilii (Henn.) Trappe & Kagan-Zur commonly known as the “Kalahari truffle” is a desert truffle species identified from the Kalahari region of southern Africa. Two other species, Eremiomyces echinulatus (Trappe & Marasas) Trappe & Kagan-Zur and Mattirolomyces austroafricanus (Trappe & Marasas) Trappe & Kovacs are also known to occur in other parts of southern Africa. Truffles are hypogeous fruiting bodies of Ascomycetes, important to humans for their nutritional value and medicinal characteristics. These truffles are known as desert truffles as they prefer to occur under arid or semi-arid conditions characteristic of deserts. Truffle development depends on the presence of a mycorrhizal host, associated microorganisms as well as soil and climatic characteristics. It has been suggested that K. pfeilii has a suspected broad plant host range which includes herbaceous to woody trees and shrubs. However, these relationships have not been verified. Indigenous people of the Kalahari believe that truffles are found under grasses. In the Kalahari, truffle fruiting bodies are often found entangled in Stipagrostis ciliata (Desf.) De Winter var. capensis (Trin. & Rupr.) De Winter roots. S. ciliata, also known as the tall bushman-grass, is the most common grass found in the Kalahari. The objective of this study was to provide conclusive evidence that S. ciliata var. capensis is a host of the Kalahari truffle. Truffle fruiting bodies and grass roots from where the truffles were found were collected from Upington, South Africa. The fruiting bodies were identified by observing their morphological characteristics using the ‘Keys of Truffle genera’. All observed physical properties were similar to those of K. pfeilii and further identification was done using molecular techniques. DNA was extracted from the fruiting bodies, mycelial cultures, rhizosheaths and from the S. ciliata var. capensis grass roots, which were then amplified using the specific K. pfeilii specific primers TPF3 and TPR1 and sequenced. The obtained sequence results confirmed that the collected fruiting bodies were those of the K. pfeilii and the molecular techniques also confirmed that K. pfeilii DNA was present in the S. ciliata var. capensis rhizosheath and root cells. Microscopy showed an ectendomycorrhizal association between K. pfeilii and S. ciliata var. capensis. Mycorrhizal resynthesis experiments were conducted to establish this mycorrhizal association in-vitro. They were unsuccessful because of the structure of the grass and the availability of contaminants. And more...

Regensburg, Univ., Diss., 2007

University, Diss., 2002--Potsdam.

Why do animals make false alarms; are false alarms truly deceptive; and if, just as in Aesop's fable 'The boy who cried wolf' , animals can learn to ignore false alarms, why doesn't deception break down? I investigated these questions in a population of habituated and individually recognisable fork-tailed drongos (Dicrurus adsimdis), in the South African Kalahari Desert. Drongos either self-foraged, when they hawked and gleaned small insects, or followed other species stealing large terrestrial prey that hosts excavated. Stealing food from other species enabled drongos to capture prey otherwise unavailable to them and accounted for over 20% of their biomass intake. This was of greatest benefit during the morning and on colder days when payoffs from stealing remained stable while those from self-foraging declined (Chapter 3). Drongos stole food using two strategies, either by physical attack or by producing false alarm calls in response to which hosts fled to cover, enabling drongos to fly down and collect abandoned food. False alarms increased overall success, and were produced when stealing small food items unprofitable to gain by physical attack, or when stealing from larger species more likely to defend food (Chapter 4). Drongos produced both their own alarm calls and mimicked alarm calls of other species in their false alarm repertoire. Playback experiments on two host species, pied babblers (Turdoides bicolor) and meerkats (Suricata suricatta), confirmed that these false alarm calls were deceptive because they were as effective at alerting hosts as true alarms given to approaching predators (Chapter 5). Further playbacks showed that hosts were more likely to be deceived by mimicked false alarm calls, including mimicry of the host species alarms, than by a drongo' s own alarms. In addition, host species habituated to repeated playback of the same alarm but resumed their response when a new alarm call was played, and drongos naturally changed their alarm calls when hosts failed to respond to a previous false alarm. Therefore, by employing vocal mimicry to vary their alarm calls drongos were both more likely to deceive hosts, and to maintain deception. Consequently drongos evaded the frequency dependent constraints which typically limit payoffs from deception when species produce only one signal (Chapter 6). The drongos sophisticated communication strategy raises questions for future research regarding the mechanisms leading to the production of complex behaviour.

Observations by local people in the Mier area, southern Kalahari, South Africa, indicated that degraded rangeland does not recover within a time frame acceptable to landowners. Pristine vegetation in this linear dune system consists largely of a herbaceous layer dominated by perennial grasses. Woody vegetation is sparse on dunes and interdunes in good condition. The dunes and interdunes react differently to disturbance, probably because of differences in substrate stability, soil particle size distribution and consequent differences in soil nutrient distribution and moisture content. Degraded dunes are devoid of any vegetation, except for Stipagrostis amabilis, a rhizomatous grass which remain in small clumps, and the tree Acacia haematoxylon. The latter increases in numbers probably due to the high moisture content in degraded dunes. Moisture content in degraded dunes remain high even during prolonged dry periods. Interdunes are more susceptible to degradation and are invaded by the long-lived shrub Rhigozum trichotomum and the annual grass Schmidtia kalahariensis. Both these species compete with perennial grasses for moisture. Additionally, depleted seed banks and increased seed predation by ants (Messor capensis) may also affect the re-establishment of perennial grasses in the interdunes. The main conclusion from this study is that degraded southern Kalahari rangeland cannot recover spontaneously at the landscape scale because of a negative feedback mechanism that prevents establishment and growth of seedlings. The hypothesis put forward is that rangeland ceases to react to rainfall as an ecosystem driver as it becomes degraded. Once degraded, wind controls the dynamics of the system and recovery, irrespective of rainfall, is almost impossible. In contrast, detailed studies at the level of small isolated populations of S. amabilis and S. ciliata on degraded dunes indicate high rates of population growth. The scales at which these processes exist are contradictory and may not be contradicting. Rangeland managers should take cognisance of the influence of the spatial and temporal scale at which they operate, and on which they base their decisions. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2000.

No description available.

Ph.D. - Geology / Geophysical, borehole and mapped data from the Kalahari Basin were used to create maps of the sub-Kalahari geology, isopachs of the Kalahari Group and basal gravels and a sub-Kalahari topographical surface. These are the first basin-wide maps of this type to be produced. These new data were interpreted with the aid of an extensive literature review as well as data gathered at three localities in the southern part of the Kalahari Basin and enabled several conclusions to be made regarding the tectonic evolution of the area. The sub-Kalahari Geological Map shows that rocks dating from the Archaean to present are exposed on the edges of the basin as well as covered by the Kalahari Group sedimentary rocks. Many of the rocks shown on the sub-Kalahari geological map record a history of rifting and subsequent collision, with the NE and SW trending structures appearing to have been reactivated at various times in the geological past. The extent of Karoo Supergroup rocks is greater than previously thought and Karoo sedimentary and volcanic rocks cover a large percentage of the sub-Kalahari surface. The Karoo Supergroup lithologies have been intruded by dolerite dykes and sills and the massive Botswana Dyke Swarm is shown on the sub-Kalahari map extending in a northwest direction across Botswana. The subtraction of the thicknesses of Kalahari Group sediments from the current topographical digital elevation model (DEM) of Africa in order to prepare a DEM of the sub-Kalahari topographical surface and the preparation of an isopach map of the basal gravels gives some indication of the courses followed by Mid-Cretaceous rivers. Topographic profiles along the proposed courses of these rivers show that the floor of the Kalahari Basin has a particularly low elevation in certain areas suggesting that downwarp of the interior of the basin rather than adjacent uplift was the driving force behind Kalahari Group sedimentation. When down-warp of the Kalahari Basin began in the Late Cretaceous these rivers were back-tilted into the newly formed basin and deposition of the Kalahari Group sediments began. The basal unit of the Kalahari Group consists of gravels deposited by the Cretaceous rivers as well as on scree slopes. As down-warp of the basin continued, so more gravels were deposited as well as the sand and -iifiner sediment carried by the rivers. Thick clay beds accumulated in the lakes that formed by the back-tilted rivers, with sandstone being deposited in braided streams interfingering with the clays and covering them in some areas as the shallow lakes filled up with sediment. During the Mid-Miocene there was a period of tectonic stability that saw the silcretisation and calcretisation of older Kalahari Group lithologies. At the end of the Miocene there was some uplift along the eastern side of southern Africa as well as along certain epeirogenic axes in the interior. In general this uplift was fairly gentle. Later more significant uplift in the Pliocene possibly elevated Kalahari Group and Karoo Supergroup sedimentary rocks above the basin floor and exposed many of them to erosion. The eroded sand was washed into the basin and reworked into dunes during drier periods. This uplift occurred along epeirogenic axes and was greater than the Miocene uplift. The development of the East African Rift System (EARS) in the Late Eocene or Oligocene has had a significant influence on the Kalahari Basin. Reactivation of older NE-SW trends by SWpropagating rifts extending from the main EARS is evident by recent movement along faults along the Damara Belt and those that were associated with Karoo sedimentation and post-Karoo graben formation. The propagating rifts have resulted in uplifting, faulting and in some cases, graben formation. In some cases lakes have formed in the grabens or half-grabens themselves and in other cases they have been formed between the uplifted arches related to parallel rifts. The propagating rifts have had a strong influence on the drainage patterns and shape of the Kalahari Basin, in particular in the middle parts of the basin where they have controlled the formation of the Okavango Delta and the Makgadikgadi pans

This study has focused on hydrogeological and hydrochemical settings of the Northern Namibian Kalahari Catchment which is the Namibian part of the Makgadikgadi-Kalahari-Catchment. Recharge has been the subject of process-understanding, quantification and regionalisation. Within the semiarid study area a bimodal surface constitution is prominent: hardrocks areas allow for fast infiltration along karsts and joints, whereas areas covered by unconsolidated sediments receive minor diffuse recharge and locally some preferred flow path recharge develops along shrinkage cracks and rootlets. Five substratum classes have been soil physically studied: Pans and vleis, brown to red soils, dune sand, soil with an aeolian influence, and calcrete. Aeolian sands are most promising for the development of direct diffuse recharge. Recharge by preferred flow might occur in all soil classes either due to joints in calcrete or structures and rootlets in soils. All soil classes contribute to indirect recharge because even the dune sand allows, albeit very locally, the generation of runoff. The occurrences of recharge through the unconsolidated soil and the hardrocks have been confirmed by hydrograph interpretation and by a study of hydrochemical data which identified groundwater of flood water and flood water after soil passage composition. Other prominent hydrochemical processes in the Kalahari are associated with the carbonate-equilibrium-system, mixing with highly mineralised water that is either sulphate (central area) or chloride dominated (fringe area) and development of sodium hydrogencarbonate water types. The latter is mostly generated by feldspar weathering. Variations of the hydrochemical compositions were observed for shallow groundwaters. They do not only reflect the recharge amount but also the recharge conditions, e.g. a wetter year is allowing more vegetation which increases the hydrogencarbonate content. Inverse determination of recharge by the chloride mass balance method gives recharge amounts between 0.2 and locally more than 100 mm/a. The least favoured recharge conditions are found for Kalahari covered areas, the largest amount occurs in the Otavi area. The distribution of recharge areas within the catchment is rather complex and regionalisation of recharge for the entire catchment was done by a forward approach using satellite images and by an inverse approach using hydrochemical data. From the inverse hydrochemical approach a basin-wide balanced recharge amount of 1.39 mm/a is achieved. The forward approach gave a basin-wide figure of 0.88 (minimum assumption) to 4.53 mm/a (maximum assumption). A simplistic groundwater flow model confirmed the results from the minimum recharge regionalisation by satellite images and the result from the hydrochemical approach. Altogether a mutually verified basin-wide recharge figure of ca. 1 mm/a turns out. / Diese Studie hat sich mit den hydrogeologischen und hydrochemischen Gegebenheiten im nordnamibischen Kalahari-Einzugsgebiet befaßt. Dabei sind Prozeßverständnis, Quantifizierung und Regionalisierung für die Grundwassserneubildung erarbeitet worden. Das semiaride Arbeitsgebiets ist durch eine bimodale Oberflächenbeschaffenheiten gekennzeichnet: Festgesteinsgebiete erlauben schnelle Infiltration entlang von Klüften und Karsthohlräumen, während Gebiete die mit Lockersedimenten überdeckt sind, wenig Neubildung über die Matrix erfahren und Makroporen nur lokal eine schnellere Neubildung erlauben. Fünf Bodenklassen sind bodenphysikalisch untersucht worden: Pfannen und Vleis, Rote und Braune Böden, Dünensande, Böden mit äolischem Einfluß und Kalkkrusten. Äolische Sand sind am vielversprechendsten für die Entwicklung von direkter Neubildung über die Matrix. Alle Bodenklassen tragen zur indirekten Neubildung bei, da sie -lokal allerdings sehr begrenzt- zum oberflächlichen Abfluß beitragen. Durch die Interpretation von Grundwasserganglinien und hydrochemischer Daten ist die Neubildungserscheinung bestätigt worden. Die dominanten hydrochemischen Prozesse in der Kalahari stehen im Zusammenhang mit dem Kalk-Kohlensäure-Gleichgewicht, der Mischung mit stärker mineralisierten Wässern (im zentralen Einzugsgebiet sulfatreich, am Rand eher chloridreich) und der Entwicklung von Natriumhydrogenkarbonatwässern (häufig durch Feldspatverwitterung). Die zeitlichen Variationen der hydrochemischen Parameter in flachen Grundwasser spiegeln nicht nur die Neubildungsmenge, sondern auch die Neubildungsbedingungen wider; in relative niederschlagsreichen Jahren steigt der Hydrogenkarbonatgehalt deutlich an in folge der üppigeren Vegetation. Die inverse Bestimmung der Grundwasserneubildung mit der Chloridbilanzmethode ergibt Neubildungswerte zwischen 0,2 und 100 mm/a. Die geringsten Werte treten dabei in Kalahari-Lockersedminet bedeckten Bereichen auf, die größten Werte treten im Otavi-Gebiet auf. Die Verteilung der Neubildung innerhalb des Arbeitsgebiets ist sehr komplex. Die Regionalisierung erfolgte mit einem fernerkundlichen und einem hydrochemischen Ansatz. Die Ergebnisse liegen für den hydrochemischen Ansatz bei 1,39 m/a und der fernerkundliche Ansatz gibt eine einzugsgebietsweite Neubildung von 0,89 (Minimumansatz) bis 4,53 mm/a (Maximumansatz). Ein vereinfachtes Grundwasserströmungsmodell bestätigt die Ergebnisse der hydrochemischen Regionalisierung und des minimalen fernerkundlichen Ansatzes. Daraus ergibt sich abschließend eine Gebietsneubildung von ca. 1 mm/a für das Arbeitsgebiet.