Search

This study investigates the Mid-Pleistocene paleoenvironment and dietary behaviour of ancient herbivores in the South African central interior, today part of the semi-arid Kalahari savanna. Analyses were undertaken of carbon (δ13C) and oxygen (δ18O) stable isotopes in tooth enamel carbonate of twelve fossil herbivore species from Layers 4b and 4a, associated with Earlier Stone Age (ESA) and transitional ESA-Middle Stone Age (Fauresmith) industries respectively, at the archaeological site of Kathu Pan 1. The data are compared with other Eearly to Mid-Pleistocene herbivore assemblages located in the central interior, namely Cornelia-Uitzoek, Wonderwerk Cave and the Florisbad Spring. Results indicate that the median δ13C values for all ungulate taxa at Kathu were >-4‰, indicating predominantly C 4 based diets, although in certain taxa, some individuals included a significant C 3 component in their diet. The δ18O values of most species at Kathu were relatively low, suggesting a cooler and/or wetter climate. Carbon isotope evidence for C 4 dominated habitats at Kathu, but with a larger C 3 component amongst grazers than today, resembles the other Early to -Mid-Pleistocene assemblages in the region. Similarly, δ18O values for Kathu supplement existing evidence that the region was substantially wetter than in modern times. [ABSTRACT FROM AUTHOR]

The balance between trees and grasses is a key aspect of savanna ecosystem functioning, and so far, believed to be regulated by resource availability, fire frequency and consumption by mammalian herbivores. Herbivores, however, also impact plant communities through the deposition of growth‐limiting nutrients in their dung and urine. Little attention has been paid to the fact that savanna herbivores produce dung containing different concentrations of nutrients and it remains unknown what the effect of this variation is on tree–grass interactions.Here, we investigate if stoichiometric differences in dung from browsers and grazers from an African savanna are large enough to influence competitive interactions between N2‐fixing trees and grasses. We performed a competition experiment with seedlings of three common N2‐fixing tree species and three common C4 grass species from a Kenyan savanna. Plants were grown in mesocosms as monocultures or mixtures with dung from either zebra (grazer) or giraffe (browser).We show that variation in dung nitrogen (N) to phosphorus (P) ratio between these herbivores was large enough to drive the competitive outcome between tree seedlings and grasses. Under zebra dung with a low N:P ratio (3.5), tree seedlings had an advantage due to increased nodulation and N2 fixation. Under giraffe dung with a high N:P ratio (6.4), grasses suppressed nodulation and tree seedling growth.Synthesis. We identify another potentially important mechanism by which mammalian herbivores can stimulate ecosystem stability, namely through the N:P ratio of their dung. This illustrates how connected browsing and grazing herbivores are in African savannas, through the forage quality they consume, the N:P stoichiometry of their dung and subsequent effects on plant competition. [ABSTRACT FROM AUTHOR]

Although dung of mammalian herbivores is an important pathway for nutrient return in savanna ecosystems, differences in dung decomposition rates among species have been little studied., We measured the rates of dung deposition and decomposition for various herbivores in a moist Tanzanian savanna and the related differences among species to nutrient concentrations and the activities of soil macrofauna (e.g. different mesh sizes of decomposition bags, or presence and absence of dung beetles)., Dung C : N : P stoichiometry varied widely among species, which could in part be explained by differences in feeding strategy (browsers vs. grazers) and digestive physiology (ruminants vs. non-ruminants). Rates of both decomposition and nutrient release were influenced by the C : N : P stoichiometry of dung, with lower relative losses of the least abundant nutrient in the dung. Surprisingly, soil macrofauna increased the relative losses of the least abundant nutrient, thereby stabilizing the ratio of N loss to P loss. Dung beetles increased rates of N and P release from wildebeest dung significantly and also increased N availability in the soil., We conclude that rates of nutrient return in dung depend not only on where herbivores deposit their dung, but also on its C : N : P stoichiometry, the activity of soil macrofauna and interactions between these factors. These factors may therefore influence the relative availabilities of N and P in the soil and hence the functioning of savanna ecosystems. [ABSTRACT FROM AUTHOR]

Bluetongue (BT) is a non-contagious, infectious, arthropod transmitted viral disease of domestic and wild ruminants that is caused by the bluetongue virus (BTV), the prototype member of the Orbivirus genus in the family Reoviridae. Bluetongue was first described in South Africa, where it has probably been endemic in wild ruminants since antiquity. Since its discovery BT has had a major impact on sheep breeders in the country and has therefore been a key focus of research at the Onderstepoort Veterinary Research Institute in Pretoria, South Africa. Several key discoveries were made at this Institute, including the demonstration that the aetiological agent of BT was a dsRNA virus that is transmitted by Culicoides midges and that multiple BTV serotypes circulate in nature. It is currently recognized that BT is endemic throughout most of South Africa and 22 of the 26 known serotypes have been detected in the region. Multiple serotypes circulate each vector season with the occurrence of different serotypes depending largely on herd-immunity. Indigenous sheep breeds, cattle and wild ruminants are frequently infected but rarely demonstrate clinical signs, whereas improved European sheep breeds are most susceptible. The immunization of susceptible sheep remains the most effective and practical control measure against BT. In order to protect sheep against multiple circulating serotypes, three pentavalent attenuated vaccines have been developed. Despite the proven efficacy of these vaccines in protecting sheep against the disease, several disadvantages are associated with their use in the field. [ABSTRACT FROM AUTHOR]

A wide range of bioenergetic, production, life history and ecological traits scale with body size in vertebrates. However, the consequences of differences in community body-size structure for ecological processes have not been explored. We studied the scaling relationships between body mass, shoulder height, hoof area, stride length and daily ranging distance in African ungulates ranging in size from the 5 kg dik-dik to the 5,000 kg African elephant, and the implications of these relationships on the area trampled by single and multispecies herbivore communities of differing structure. Hoof area, shoulder height and stride length were strongly correlated with body mass (Pearson's r >0.98, 0.95 and 0.90, respectively). Hoof area scaled linearly to body mass with a slope of unity, implying that the pressures exerted on the ground per unit area by a small antelope and an elephant are identical. Shoulder height and stride length scaled to body mass with similar slopes of 0.32 and 0.26, respectively; larger herbivores have relatively shorter legs and take relatively shorter steps than small herbivores, and so trample a greater area of ground per unit distance travelled. We compared several real and hypothetical single- and multi-species ungulate communities using exponents of between 0.1 and 0.5 for the body mass to daily ranging distance relationship and found that the estimated area trampled was greater in communities dominated by larger animals. The impacts of large herbivores are not limited to trampling. Questions about the ecological implications of community body-size structure for such variables as foraging and food intake, dung quality and deposition rates, methane production, and daily travelling distances remain clear research priorities. [ABSTRACT FROM AUTHOR]