Goat browsing does not induce physical defences but reduces leaf size in Vachellia trees
- Authors: Nzimande, Amanda , Mgqatsa, Nokubonga , Kraai, Unathi M , Tsvuura, Zivanai , Kraai, Manqhai
- Date: 2022
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/462624 , vital:76320 , xlink:href="https://doi.org/10.1016/j.actao.2022.103818"
- Description: One aspect of plant-herbivore interactions in African savannas is the browsing impact of mammalian herbivores on plants, which may result in induced physical defences (spines) and changes in leaf morphology in trees experiencing intensive browsing. In these savannas, spinescence is considered to have evolved in response to herbivore pressure from large mammals. We assessed the impact of free-ranging domesticated goats on the spines and leaves of Vachellia karroo, V. nilotica and V. tortilis in Msinga, South Africa. We predicted that there would be fewer and smaller leaves, and longer spines occurring below compared to above 1.5 m for all tree species. We further predicted that the outer parts of the tree canopy would have smaller and fewer leaves, as well as more and longer spines compared to the inner part of the canopy. To determine the response of these trees to goat herbivory, 35 trees of each Vachellia species were selected, the number of leaves and spines found on two randomly selected branches below 1.5 m and one above 1.5 m were measured. We found that leaves were fewer and smaller below compared to above 1.5 m. Interestingly, we found the reduced leaf size to be equal to the size of spines below 1.5 m. We also found that V. karroo had more spines below 1.5 m compared to V. tortilis and V. nilotica. Along the branch segments, we found that spines were longer in the most accessible parts of the branch, the outer canopy. This study showed that browsing by goats, unlike wild herbivores, do not induce plant physical defences but rather limit available foliage. We also showed that physical defences (spine density) of Vachellia trees vary. This has implications for management and ecology of rangelands browsed by domestic mammals.
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- Date Issued: 2022
White rhinoceros populations in the Eastern Cape: distribution, performance and diet
- Authors: Kraai, Manqhai
- Date: 2010
- Subjects: Rhinoceroses -- South Africa -- Eastern Cape , Rhinoceroses -- Habitat -- South Africa -- Eastern Cape , Rhinoceroses -- Behavior -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10692 , http://hdl.handle.net/10948/1297 , Rhinoceroses -- South Africa -- Eastern Cape , Rhinoceroses -- Habitat -- South Africa -- Eastern Cape , Rhinoceroses -- Behavior -- South Africa -- Eastern Cape
- Description: White rhino populations did not occur historically in the Eastern Cape, South Africa (Skead 2007). They have, however, been introduced into a number of reserves within the Eastern Cape for reasons such as conservation, ecotourism and hunting. Based on the literature on the species, it was hypothesized that white rhinoceros would have been introduced in grass-rich habitats, as they are bulk grazers. White rhinoceros populations were further assessed in terms of population establishment by outlining their distribution and performance since introductions and this was done by extracting intercalving intervals from the literature of native populations and comparing such to the Eastern Cape intercalving intervals, extracted from data obtained from landowners. Finally, the diet of white rhinoceros was quantified, in order to identify plant species potentially at risk from white rhino herbivory using Shamwari Private Game Reserve as a study site. The distribution of white rhino in the Eastern Cape varies in terms of habitat and vegetation types. The majority (62%) of white rhino are located in grass-poor habitats and are primarily there for ecotourism purposes with only a small percentage kept for conservation purposes in the state reserves. Limited data for intercalving intervals of the white rhino in Eastern Cape are comparable to those of populations in the natural range. The ex situ conservation of white rhino in the Eastern Cape proved to be a success as population numbers have increased markedly since the first survey was conducted (Buijs 1999). The diet section of this study showed that white rhino are highly selective grazers even in a grass-limiting habitat which is dominated by browse. Twenty-five principal dietary items were identified in their diet, with only six being preferred in autumn. These are thus the plant species that could be the most vulnerable to white rhino herbivory. Supplementary food provision plays a big part of the feeding scheme of white rhino in Shamwari Private Game Reserve during the winter season, revealing the little confidence that the management has on natural resource availability to the animals at this time. These findings support the value of the Eastern Cape for ex situ conservation of white rhino, and highlight plant species potentially at risk. There is a need for further research on the population performance of these animals, and the plants identified here need to be monitored to assess white rhino impact on the vegetation
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- Date Issued: 2010