Elephants and water provision: what are the management links?

In a recent paper we demonstrated that elephant bull groups and mixed herds exhibited spatial and resource segregation across the Kruger National Park. It was found, inter alia , that both bull groups and mixed herds occurred more frequently closer to rivers than expected if they were randomly distributed, but that only bull groups occurred more frequently closer to the artificial waterholes. Although Chamaillé-Jammes et al. (2007 ) accepted these results, they disagreed with our interpretation regarding the potential effect that closure of artificial waterholes might have. Here we address some of the specific concerns expressed and provide a broader context regarding water provision and elephant management. Although water provision can influence elephant density and distribution, we argue that the effectiveness of surface-water manipulation as a management tool will depend on (1) natural surface-water availability, (2) forage quality, (3) elephant densities, (4) position of a population on its growth trajectory, and (5) management objectives. Even though elephants are water-dependent, the effectiveness of water provision as a management tool will therefore be area- and population-specific and will depend on management objectives.     

Effects of body size on the diurnal activity budgets of African browsing ruminants

We compared the diurnal activity budgets of four syntopic species of African browsing ruminant that differ widely in body size. These were concurrently studied through all phases of the seasonal cycle, in the same area, using the same methods. We tested five predictions from the literature on how body size is expected to influence the behaviour of tropical ungulates: the smallest members of the browsing ruminant guild exhibit (1) the lowest allocation of diurnal time to activity; (2) the greatest hour-to-hour variation in activity and resting time; (3) the greatest reduction in activity time during the hottest days; (4) the least change between wet and the dry seasons in the ratio of feeding: ruminating time; and (5) the greatest time budget allocation to vigilance. Prediction 1 was supported in that the smaller species spent less time being active during the day. Prediction 2 was also supported in that the smaller species were more variable in their relative allocations of time to activity and resting through successive hours of the day. Contrary to Prediction 3, however, the greatest reduction in activity with increasing temperature was found for the largest guild member. The smaller species can achieve their daily food intake requirements by feeding at night and in the cool hours of the day, while the larger species have to feed during all hours of the day and are thus more susceptible to thermoregulatory constraints on foraging. Prediction 4 was partially upheld in that the largest species (giraffe) displayed the widest variation in feeding: ruminating time through the seasonal cycle. Prediction 5 was not supported, indicating that multiple factors interact with body size in determining vigilance behaviour.     

Roan (Hippotragus equinus) population decline in Kruger National Park, South Africa: influence of a wetland boundary

Effective management of grazers requires understanding of the mechanisms influencing population declines. Roan antelope, a specialist grazer, has declined in population numbers within Kruger National Park, South Africa. The most widely accepted hypothesis is that habitat deterioration throughout the entire northern plains landscape is responsible for declines in this species. Observations suggest, however, that on the northern plains of Kruger National Park, roan antelope grazes at the boundary between ephemeral wetland and the savanna matrix. The boundary is characterized by nutrient-rich soil and forage, and thus attracts grazing from both generalist and specialist species. We hypothesize that competition for resources at this ecotone, and not at other places in the landscape, is responsible for the observed declines in roan antelope. Changing management strategies to be more cognizant of patchiness and savanna heterogeneity, i.e. more spatially informed, will improve the likelihood that management will result in increasing roan population numbers.     

Hominins, sedges, and termites: new carbon isotope data from the Sterkfontein valley and Kruger National Park

Stable carbon isotope analyses have shown that South African australopiths did not have exclusively frugivorous diets, but also consumed significant quantities of C4 foods such as grasses, sedges, or animals that ate these foods. Yet, these studies have had significant limitations. For example, hominin sample sizes were relatively small, leading some to question the veracity of the claim for australopith C4 consumption. In addition, it has been difficult to determine which C4 resources were actually utilized, which is at least partially due to a lack of stable isotope data on some purported australopith foods. Here we begin to address these lacunae by presenting carbon isotope data for 14 new hominin specimens, as well as for two potential C4 foods (termites and sedges). The new data confirm that non-C3 foods were heavily utilized by australopiths, making up about 40% and 35% of Australopithecus and Paranthropus diets respectively. Most termites in the savanna-woodland biome of the Kruger National Park, South Africa, have intermediate carbon isotope compositions indicating mixed C3/C4 diets. Only 28% of the sedges in Kruger were C4, and few if any had well-developed rhizomes and tubers that make some sedges attractive foods. We conclude that although termites and sedges might have contributed to the C4 signal in South African australopiths, other C4 foods were also important. Lastly, we suggest that the consumption of C4 foods is a fundamental hominin trait that, along with bipedalism, allowed australopiths to pioneer increasingly open and seasonal environments.     

Relative pollen productivity and fall speed estimates for southern African savanna taxa

Understanding the characteristics of pollen dispersal and deposition of different plant taxa is crucial to accurately reconstructing past landscapes using fossil pollen data. Quantitative reconstruction of past landscapes from pollen data using the Prentice-Sugita approach requires estimates of fall speed and relative pollen productivity for all taxa modelled. This study presents estimates of pollen productivity and fall speeds for key southern African savanna taxa, providing a basis for the improved interpretation of fossil pollen records from this extensive and heterogeneous biome. The work was carried out in 5 steps. (1) Modern pollen assemblages from 34 surface sediment samples were analysed. (2) Vegetation around each sampling site was surveyed in concentric circles to a radius of 50 m, and data from existing park surveys were analysed to extend the survey distance to 5 km. (3) Fall speeds for the main pollen taxa were estimated using Stoke’s Law of particle settling velocity. (4) Vegetation data were weighted using three different distance-weightings, one incorporating the different particle fall speeds. (5) Extended R-Value analysis was carried out on the pollen and distance-weighted plant abundance datasets using HUMPOL software to estimate relevant source area and relative pollen productivity for the main pollen taxa present. Results showed the Relevant Source Area of Pollen surrounding the sites to be 600–900 m radius, and Poaceae/Cyperaceae were found to be twice as productive (PPE 2.03) as the arboreal taxa analysed (PPE 0.50–0.99). The problems encountered in calculating pollen productivity estimates in savanna environments are discussed and improvements for future studies are suggested.     

Thresholds of potential concern as benchmarks in the management of African savannahs

In the Kruger National Park (KNP), South Africa, ecosystem managers use a series of monitoring endpoints, known as thresholds of potential concern (TPCs), to define the upper and the lower levels of accepted variation in ecosystems. For woody vegetation, the current TPC suggests that woody cover should not drop by more than 80% of its 'highest ever' value. In this paper, we explore the utility of palaeoecological data in informing TPCs. We use calibrated fossil pollen data to explore variability in vegetation at two sites over the past 5000 years, to provide a long-term record of changes in woody vegetation cover and a context for interpreting more recent vegetation change. The fossil pollen data are calibrated using studies of modern pollen and vegetation from KNP; arboreal pollen percentage was simulated using pollen-landscape modelling software for savannah landscapes of varying woody vegetation cover, and the relationship between vegetation and pollen data was quantified using nonlinear regression. This quadratic equation was then applied to fossil pollen data in order to estimate woody vegetation cover from arboreal pollen percentages. Our results suggest that the TPCs have not been exceeded during the period represented in the pollen record, because estimated woody vegetation cover has remained above 20% of its highest ever value. By comparing the fossil pollen data with TPCs, our study demonstrates how palaeoecological data can be presented in a form that is directly relevant to management objectives.