Michael H. Knight

Desertification of subtropical thicket in the Eastern Cape, South Africa : are there alternatives ?

The Eastern Cape Subtropical Thicket (ECST) froms the transition between forest, semiarid karroid shrublands, and grassland in the Eastern Cape, South Africa. Undegraded ECST forms an impenetrable, spiny thicket up to 3 m high consisting of a wealth of growth forms, including evergreen plants, succulent and deciduous shrubs, lianas, grasses, and geophytes. The thicket dynamics are not well understood, but elephants may have been important browsers and patch disturbance agents. These semiarid thickets have been subjected to intensive grazing by domestic ungulates, which have largely replaced indigenous herbivores over the last 2 centuries. Overgrazing has extensively degraded vegetation, resulting in the loss of phytomass and plant species and the replacement of perennials by annuals. Coupled with these changes are alterations of soil structure and secondary productivity. This rangeland degradation has largely been attributed to pastoralism with domestic herbivores. The impact of indigenous herbivores differs in scale, intensity, and nature from that of domestic ungulates. Further degradation of the ECST may be limited by alternative management strategies, including the use of wildlife for meat production and ecotourism. Producing meat from wildlife earns less income than from domestic herbivores but is ecologically sustainable. The financial benefits of game use can be improved by developing expertise, technology, and marketing. Ecotourism is not well developed in the Eastern Cape although the Addo Elephant National Park is a financial success and provides considerable employment benefits within an ecologically sustainable system. The density of black rhinoceros and elephant in these thickets is among the highest in Africa, with high population growth and the lowest poaching risk. The financial and ecological viability of ecotourism and the conservation status of these two species warrant expanding ecotourism in the Eastern Cape, thereby reducing the probability of further degradation of ECST.

Energy, Water, and Food Use by Springbok Antelope (Antidorcas marsupialis) in the Kalahari Desert

Field-metabolic rates and water-influx rates (both measured via doubly-labeled water) and diet composition (rumen contents, plant sample analyses) were measured in free-ranging male springbok antelope ( Antidorcas marsupialis ) during the three seasons of the Kalahari. Results from springbok that did not drink water during the hot, dry season indicate that they can achieve water balance without drinking if they can obtain plant food containing at least 67% water. Springbok may accomplish this by selecting flowers, seeds, and leaves of shrubs (mainly Acacia mellifera and A. hebeclada ) before dawn, when these foods are most succulent. Springbok ate mostly grass during the hot seasons if drinking water was available, but, in the cold, dry season, their selection of succulent shrub leaves (mainly A. mellifera ) apparently made them independent of drinking water. During the rut, males had high energy and water requirements and lost weight because they did not eat enough food to maintain balance. During most of the year, springbok used water and energy at comparatively low rates, in common with other desert-adapted mammals. Their water-economy index also was low, indicating a conservative water metabolism. We estimated that an adult male springbok consumes ca. 504 kg (dry matter) of food/year and that the population of springbok consumed ca. 76% of the annual grass productivity within the important, dry riverbed habitats. Competition with other large grazers, and particularly with those restricted to foraging in close proximity to drinking water, probably existed during the dry years of this study.

Seasonal and circadian energetic patterns in an arboreal rodent, Thallomys paedulcus, and a burrow-dwelling rodent, Aethomys namaquensis, from the Kalahari Desert

Abstract 1. 1. Thermal energetic profiles as a function of the maximum range of ambient air temperatures ( T a ) over which normothermia could be maintained, were measured in an arboreal rodent, Thallomys paedulcus , and a burrow-dwelling rodent, Aethomys namaquensis , during the rest- and activity-times, and in summer- (LD 16:8, 30°C) and winter-acclimated (LD 8:16, 20°C) animals. 2. 2. Both species had minimal wet thermal conductances ( C min ) ca 42% of expected values, and thermoneutral resting metabolic rates (TRMR) 54–64% of expected values. It is proposed that the low C min s are required to maintain thermal balance at the lowest daily T a s, whereas the low TRMRs are required to avoid hyperthermia induced by high daily T a s and the low C min values. 3. 3. Burrowing behaviour did not seem to influence the selection of these low parameters per se , but did require large seasonal fluctuations in the endothermic temperature range—the maximum range of T a over which the animal maintained normothermia below thermoneutrality. 4. 4. It is suggested that a continuum may exist between the water-economy hypotheses and our endothermic temperature range hypothesis, dependent upon the refugia used, diet, water availability, and heat tolerance.

Evaluating population persistence of censused and unmanaged herbivore populations from the Kruger National Park, South Africa

Abstract The application of the Dennis et al. (Ecol. Monogr., 61, 1991) model to data from 12 herbivore populations from the Kruger National Park, South Africa, introduces ‘risk assessment’ procedures into the conservation management of free-ranging species. The model enables one to predict the probability of reaching an arbitrarily defined threshold population size using census figures from censused and unmanaged populations. It also provides an objective evaluation of population persistence based on past performance. Of the 12 species investigated, five (impala Aepyceros melampus, blue wildebeest Connochaetes taurinus, zebra Equus burchelli, white rhinoceros Ceratotherium simum, giraffe Giraffa camelopardalis) appear to be secure, four (kudu Tragelaphus strepsiceros, waterbuck Kobus ellipsiprymnus, warthog Phacochoerus aethiopicus, sable antelope Hippotragus niger) are vulnerable and three species (tsessebe Damaliscus lunatus, eland Taurotragus oryx, roan antelope Hippotragus equinus) are at risk of declining by an order of magnitude within 100 years. Therefore, within data limitations, the KNP appears not to offer sufficient suitable habitat for a number of herbivore species despite its considerable size, and a metapopulation approach may be required for the effective conservation of some species. The model also allows the principle of ‘complementarity’ to be extended beyond that of species composition. Objective evaluations of population persistence, of censused and unmanaged populations, as demonstrated here, mean that the principle of ‘population viability’ can help the design of efficient regional reserve networks.

Conservation targets for viable species assemblages

Estimates of minimum areas required for effective biodiversity conservation differ substantially. Scientific reserve design and placement procedures indicate that between 30 and 75% of any region may be required to sample biodiversity features. These estimates do not routinely incorporate measures for sampling viable populations of species or explore the area requirements of sampling viable populations of species assemblages. To determine the area requirements for sampling viable populations of a herbivore assemblage, spatially explicit abundance data from the Kruger National Park, South Africa, were analyzed. Area requirements were consistently above 50% and were unaffected by selected target population sizes. In addition, area requirements appeared to be insensitive to selection unit size (analytical grain), habitat quality, the coarseness of the land classification system used or the presence of low-density species. Thus, traditional conservation area targets of 10–15% appear inadequate for representing viable populations of a herbivore assemblage from African savanna regions. This suggests that conservation targets of at least 50% of land classification units may represent a more appropriate conservation rule of thumb, or alternatively, that the use of data independent conservation targets may need to be abandoned.

Comparative field energetics of a kalahari skink (Mabuya striata) and gecko (Pachydactylus bibroni)

Many diurnal lizards maintain comparatively high body temperatures by means of behavioral thermoregulation. They should have higher daily integrated body temperatures, and hence higher daily energy and food requirements than nocturnal lizards, which have lower body temperatures when active. We tested this hypothesis with a diurnal skink and a nocturnal gecko, both of which are arboreal insectivores. Doubly labeled water measurements indicate that field metabolic rates (FMR), water flux rates, and feeding rates do not differ between these two sympatric Kalahari lizards. Our results suggest that geckos: 1) may have higher body temperatures during the daytime; 2) may be more active while abroad; 3) may be abroad longer each day; and, 4) may have different thermal effects on their energy metabolism than previously thought.

Evaluating herbivore extinction probabilities in Addo Elephant National Park, South Africa

Population extinction evaluations, based on the model developed by Dennis et al. (1991) that did not take density dependence into account and that were based on census data, suggest that many of the herbivore species in Addo Elephant National Park (AENP) are vulnerable to local extinction. As a result of low abundance, grysbok and bushpig populations are likely to become extinct within the next ten years. Species such as the common duiker, eland, buffalo, ostrich and bushbuck are likely to go extinct within the next 60 years, whereas populations such as the black rhino, kudu and red hartebeest appear less vulnerable and display an insignificant probability of local extinction. This conclusion was supported by the absence of discernible density-dependence effects in all but one of the species included in the analyses. In addition, population variance parameters (F2 of herbivore species from AENP, were larger than those recorded from the Kruger National Park and various elephant populations from South Africa. These data suggest that strict adherence to the management objectives, by managing for increasing mega-herbivore populations (elephant, black rhino) in AENP may have been responsible for increasing the risk of local extinction of other herbivore populations. Consequently, should the objectives of AENP be amended to incorporate broader biodiversity objectives, the recent extension of AENP, which increased habitat heterogeneity in the Park, may prove timely.