Browsing by Author "Vetter, Susanne"
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- ItemOpen AccessInvestigating the impacts of donkeys on a communal range in Namaqualand: how much does a donkey "cost" in goat units?(1996) Vetter, Susanne; Bond, William J; Hoffmann, TimmDonkeys are used extensively in Namaqualand and other rural areas in South Africa for pulling carts, carrying loads, ploughing and threshing grain. There is, however, an ongoing debate among farmers, agriculturalists and the wider population about the implications of keeping donkeys, particularly on communal lands. Donkeys are reported to cause more damage to the veld than other animals, and it is commonly said that one donkey eats as much as seven goats. This project was initiated as a case study to investigate the impacts of donkeys in a communal area in the succulent shrublands of Namaqualand, and to generate suggestions for the management of donkey populations. The degree of competition between goats and donkeys was investigated by predicting daily food intake using a model based on ruminant and non-ruminant digestion, which takes into account the animal's body weight and digestibility characteristics of its diet. The ratio predicted food intakes is discussed in the light of the degree of dietary and habitat overlap, which were obtained from field observations. Habitat use was scored using dung frequency transects, and feeding was directly observed. It was found that in the wet season, one donkey eats as much as 5 / 7.6 goats (donkey weight set at 200 and 250 kg respectively). In the dry summer, this ratio increases to 7.6 / 8.6 because in ruminants, the passage of food through the gut slows down as the digestibility of the diet decreases. Habitat overlap is concentrated in the riverine areas and sandy pediments, which make up 15 % of the landscape and are strongly favoured by donkeys. No significant differences were found to exist between the intensities of goat use of the different habitats. The botanical composition of the diets of donkeys and goats were found to be similar, but there is a great difference in the quality of the diet consumed by each species as goats are able to select plant parts of a higher quality. The implications of this are that whereas a donkey takes in as much dry matter as 5 - 8.6 goats, the diet of this food is not high enough to satisfy the dietary requirements of goats, and hence fewer goats than predicted can be supported for every donkey that is eliminated. Donkeys are commonly reported to have destructive feeding habits; little of this was directly observed, but donkeys were found to bite deeper into the wood of shrubs, which may damage the plants in the long term. There are two main management measures that should be applied. The feral donkey population in Paulshoek, estimated at 50-100 animals, must be eliminated - even at a conservative estimate, these animals could be replaced with 250 goats. However, one must look beyond the number to the processes taking place to make management effective. Even if one donkey can be replaced with fewer than 5 goats, the vegetation is relieved of the indirect effects donkeys have through their feeding habits. Control of working donkeys should focus on the riverine and flat, sandy areas, as they are potentially of high nutritional importance (especially the riverine areas which support grass throughout the year), and which are also the most susceptible to erosion due to their sparse vegetation cover. These areas are small and valuable, and plans should be made to protect some areas through the growing season.
- ItemOpen AccessThe potential of Grateloupia filicina (Lamouroux) J. Agardh. for mariculture: culture experiments and observations on shore phenology(1996) Vetter, Susanne; Bolton, John J; Anderson, Robert JGrateloupia filicina is a carrageenophytic red alga which is in demand as a carrageenan raw material and for use in food. There is therefore interest in developing a technique for mariculturing this species. Since vegetative propagation from thallus fragments has not been successful, the present study was initiated to determine suitable conditions for spore liberation and growth of G. filicina from spores. It was also attempted to propagate G. filicina sporelings from crust and thallus fragments. In addition, the proportions of plants in different life history phases were determined in August and September to test for seasonal differences in shore phenology, and whether G. filicina is monoecious or dioecious, since there is disagreement on this in the literature. Spore release was easy to achieve, even without stressing the parent plant. Growth of crusts was found to be fastest at 50 μM.m⁻².s⁻¹ and at 20°C. Carposporelings (i.e. young tetrasporophytes) grew slightly but significantly faster than tetrasporelings (i.e. young carposporophytes). Crust fragments were able re-attach to the substrate and gave rise to new upright thalli within 1-2 weeks, compared to 4-5 weeks between spore release and thallus initiation. Attachment was weak, however, and only a small proportion of the crust fragments placed into culture regenerated. Thallus regeneration was not successful. There were seasonal differences in shore phenology during the study period: while two thirds of the plants collected in August were carposporophytes, only tetrasporophytes were found in September. No male gametophytes or spermatangia were found. It did not emerge from this study whether G. filicina in an annual, or what phenotypic differences are found throughout the year. Information of this kind is important for mariculture as it affects the supply of parent plants (and therefore spores) and the growth of young plants on ropes if these are released into the sea. The culturing experiments look promising; techniques (seeding ropes directly with spores or using regenerated crust fragments) still need to be refined.
- ItemOpen AccessWhat are the cost of land degradation to communal livestock farmers in South Africa : the case of the Herschel District, Eastern Cape(2003) Vetter, Susanne; Bond, William J; Trollope, WinstonA more recent approach to communal rangelands argues that this traditional view has ignored communal farmers' objectives, which are to maximise stock numbers rather than offtake in the form of sales and slaughter, and challenges the view that communal rangelands are necessarily degraded. Long-term livestock records in many former homeland districts of South Africa have shown no appreciable long-term decline in animal numbers. This has led several influential researchers and policy makers to conclude that no loss in productivity has occurred and that these systems are sustainable in fulfilling the objectives of the land users. The aim of this study is to assess the costs of degradation in terms of land users' objectives using a case study in a communal rangeland area in South Africa.