Energy maximisation strategies of different African herbivores in a fire dominated and nutrient poor grassland ecosystem
- Authors: Brooke, Christopher
- Date: 2018
- Subjects: Grassland ecology -- South Africa -- Eastern Cape , Animals -- Food -- South Africa -- Eastern Cape , Herbivores -- Ecology -- South Africa -- Eastern Cape , Fire ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/21961 , vital:29807
- Description: Fire and herbivory are both major drivers in grassland ecosystems throughout the world. Although these two driving forces act independently from one another the relationship between fire and herbivory may be more significant than either acting on their own. Heterogeneity within the landscape as a result of fire results in herbivores having to adapt their behaviour in space and time. My research focussed on 1) characterising the fire regime on Mkambati Nature Reserve (hereafter Mkambati) and 2) determining the foraging choices and energy maximisation principles displayed by herbivores in relation to the biomass of vegetation and post fire vegetation age. Fire regimes were characterised between 2007-2016 in the low nutrient coastal grasslands of Mkambati in terms of fire season, seasonality of fire-prone weather conditions, fire return interval (FRI) and influence of poaching-related ignitions. Based on these results I then assessed foraging choices in terms of energy maximisation of four large herbivore species. I explored what energy maximisation strategy was employed, i.e. maximisation of daily digestible energy (DDE) (recently burnt low biomass vegetation) or instantaneous digestible energy (IDE) (older high biomass vegetation), by herbivore species with different morpho-physiological traits. Common reedbuck (Redunca arundinum), red hartebeest (Alcelaphus buselaphus subsp. caama), zebra (Equus quagga) and eland (Tragelaphus oryx subsp. oryx) were fitted with GPS satellite tracking collars, and hourly GPS locations (observed) were taken between 2008 and 2016. Using mixed effects models, I compared observed and an associated set of random locations to determine the energy maximisation strategy employed by each species. Our results indicated that fires were concentrated in winter when monthly fire danger weather (FDI) was highest. The mean FRI at Mkambati was <3 years, but varied according to vegetation type, and whether censoring (for open ended FRIs) was applied to estimate mean FRIs. Poachers, with the intention of attracting ungulates, are an important source of ignition at Mkambati. Accordingly FRIs were shorter (approximately 2 years) in areas within 3 km of likely poacher entry points. Although all fires recorded at Mkambati during the study period were of anthropogenic origin, mean FRI still fell within the natural range reported for interior grasslands in South Africa. Based on these findings, underpinned by the fire regime information, I showed that red hartebeest and zebra maximised DDE inside and outside of fire seasons and frequently foraged in low biomass recently burnt grasslands. Eland generally favoured areas where they could maximise IDE outside of the fire season, however during the fire season they switched strategy to maximise DDE. Reedbuck did not maximise IDE or DDE at the same scale (patch scale) as the other species, but at a landscape (broader) scale they maximised both IDE and DDE. Through this research I have shown how regular fire affects the foraging and energy maximisation behaviour of large African herbivores and how morpho-physiological traits affect these decisions. In response to these results I recommend that the management of Mkambati implement a focused monitoring program comparing the frequently and less frequently burnt areas of the reserve in order to understand the complex effects of anthropogenic fire and its subsequent effects on the biota of Mkambati.
- Full Text:
- Date Issued: 2018
- Authors: Brooke, Christopher
- Date: 2018
- Subjects: Grassland ecology -- South Africa -- Eastern Cape , Animals -- Food -- South Africa -- Eastern Cape , Herbivores -- Ecology -- South Africa -- Eastern Cape , Fire ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/21961 , vital:29807
- Description: Fire and herbivory are both major drivers in grassland ecosystems throughout the world. Although these two driving forces act independently from one another the relationship between fire and herbivory may be more significant than either acting on their own. Heterogeneity within the landscape as a result of fire results in herbivores having to adapt their behaviour in space and time. My research focussed on 1) characterising the fire regime on Mkambati Nature Reserve (hereafter Mkambati) and 2) determining the foraging choices and energy maximisation principles displayed by herbivores in relation to the biomass of vegetation and post fire vegetation age. Fire regimes were characterised between 2007-2016 in the low nutrient coastal grasslands of Mkambati in terms of fire season, seasonality of fire-prone weather conditions, fire return interval (FRI) and influence of poaching-related ignitions. Based on these results I then assessed foraging choices in terms of energy maximisation of four large herbivore species. I explored what energy maximisation strategy was employed, i.e. maximisation of daily digestible energy (DDE) (recently burnt low biomass vegetation) or instantaneous digestible energy (IDE) (older high biomass vegetation), by herbivore species with different morpho-physiological traits. Common reedbuck (Redunca arundinum), red hartebeest (Alcelaphus buselaphus subsp. caama), zebra (Equus quagga) and eland (Tragelaphus oryx subsp. oryx) were fitted with GPS satellite tracking collars, and hourly GPS locations (observed) were taken between 2008 and 2016. Using mixed effects models, I compared observed and an associated set of random locations to determine the energy maximisation strategy employed by each species. Our results indicated that fires were concentrated in winter when monthly fire danger weather (FDI) was highest. The mean FRI at Mkambati was <3 years, but varied according to vegetation type, and whether censoring (for open ended FRIs) was applied to estimate mean FRIs. Poachers, with the intention of attracting ungulates, are an important source of ignition at Mkambati. Accordingly FRIs were shorter (approximately 2 years) in areas within 3 km of likely poacher entry points. Although all fires recorded at Mkambati during the study period were of anthropogenic origin, mean FRI still fell within the natural range reported for interior grasslands in South Africa. Based on these findings, underpinned by the fire regime information, I showed that red hartebeest and zebra maximised DDE inside and outside of fire seasons and frequently foraged in low biomass recently burnt grasslands. Eland generally favoured areas where they could maximise IDE outside of the fire season, however during the fire season they switched strategy to maximise DDE. Reedbuck did not maximise IDE or DDE at the same scale (patch scale) as the other species, but at a landscape (broader) scale they maximised both IDE and DDE. Through this research I have shown how regular fire affects the foraging and energy maximisation behaviour of large African herbivores and how morpho-physiological traits affect these decisions. In response to these results I recommend that the management of Mkambati implement a focused monitoring program comparing the frequently and less frequently burnt areas of the reserve in order to understand the complex effects of anthropogenic fire and its subsequent effects on the biota of Mkambati.
- Full Text:
- Date Issued: 2018
Patterns and determinants of species richness in mesic temparate grasslands of South Africa
- Authors: Hoare, David Barry
- Date: 2009
- Subjects: Grassland ecology -- South Africa -- Eastern Cape , Plant diversity -- South Africa -- Eastern Cape , Vegetation and climate
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10613 , http://hdl.handle.net/10948/1275 , Grassland ecology -- South Africa -- Eastern Cape , Plant diversity -- South Africa -- Eastern Cape , Vegetation and climate
- Description: The aim of this study is to gain a predictive understanding of the patterns and determinants of plant biodiversity in temperate, mesic grasslands of South Africa with a primary focus on the geographical area of the Eastern Cape. From a review of the literature on hypotheses explaining diversity (Chapter 2) it was possible to formulate a number of hypotheses that could be tested to explain species richness patterns in Eastern Cape grasslands. This thesis is organised so that each main chapter deals with a specific body of theory concerning the explanation of diversity patterns. A detailed description of the study area is provided (Chapter 3), including environmental variation and a description of major vegetation patterns. A summary is provided of grassland plant community patterns, as determined by phytosociological studies in the study area. A multivariate analysis of environmental variables was undertaken to determine which variables contributed the most towards explaining environmental variation in the study area and to determine whether any variables co-vary, a possible problem for any multivariate analysis in later chapters. Altitude produced one of the strongest gradients in the study area. There were a number of variables that were correlated with altitude, most notably temperature. Rainfall co-varied partially with altitude, but there was also a strong rainfall gradient perpendicular to the altitude gradient. A description of species richness, diversity and evenness patterns at the plot scale within different grassland plant communities of the Eastern Cape is provided in Chapter 4. To determine whether the environment acts differently on different growth forms, the contribution to species richness by different major growth forms is analysed. Furthermore, since the majority of literature attempts to explain diversity in terms of environmental factors, it was necessary to analyse the relationship between species richness and various environmental variables. The results indicate that there is high variation in species richness both within and among grassland communities. Forbs make the most significant contribution to overall species richness per 100 m2, followed by grasses. Variance in richness of all species together is not significantly related to environmental variables in mesic grasslands, but is significantly related to environmental variables in semi-arid grasslands. The result of greatest interest from this chapter is the fact that richness amongst different life-forms in the same place is explained by different environmental factors, indicating that the environmental factors that affect coexistence of species have a different effect on different life-forms. A classification of all the species of the dataset into plant functional types using a multivariate approach based on functional traits was conducted (Chapter 5). The grass species were classified into 16 functional types and the forbs into 14 functional types. The functional type classification provided the opportunity for undertaking analyses to develop an understanding of 8 the contribution by niche differentiation towards promoting species richness (Chapter 6). The results provide evidence of niche differentiation in the grasslands of the study area and also that niche differentiation promotes species richness in the grasslands of the study area. It was found that higher rainfall grasslands are less structured by niche differentiation than semi-arid grasslands. A regional / historical analysis is undertaken (Chapter 7) to investigate the relationship between the regional species pool and local richness, and the relationship between local richness and phytochorological diversity. Regional richness appears to have little effect in promoting local richness in grassland plant communities of the study area except at sites where there is high local richness. This provides an indication that regional richness only promotes local richness in the absence of local limiting factors. Phytochorological diversity promotes local richness, but mostly through diversity amongst species with narrow distribution ranges. Some theories ascertain that seasonal uncertainty may provide opportunities to species that would otherwise be outcompeted and thereby promote local richness. The degree to which seasonal uncertainty and seasonality promote local richness in the Eastern Cape grasslands was therefore investigated (Chapter 8). A weak relationship exists between these variables and local species richness in grassland communities of the study area, indicating that they do not promote niche differentiation to a significant degree in the study area. It is clear that in the grasslands of the Eastern Cape, environmental limiting factors are more important in semi-arid grasslands and species interactions are more important in mesic grasslands for structuring plant communities (Chapter 9, Discussion). Regional processes do not appear to be important in structuring local communities, but the analysis undertaken in this study shows that they may be significant when factors operating at the other two levels are overcome (species interactions and environmental limiting factors.
- Full Text:
- Date Issued: 2009
- Authors: Hoare, David Barry
- Date: 2009
- Subjects: Grassland ecology -- South Africa -- Eastern Cape , Plant diversity -- South Africa -- Eastern Cape , Vegetation and climate
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10613 , http://hdl.handle.net/10948/1275 , Grassland ecology -- South Africa -- Eastern Cape , Plant diversity -- South Africa -- Eastern Cape , Vegetation and climate
- Description: The aim of this study is to gain a predictive understanding of the patterns and determinants of plant biodiversity in temperate, mesic grasslands of South Africa with a primary focus on the geographical area of the Eastern Cape. From a review of the literature on hypotheses explaining diversity (Chapter 2) it was possible to formulate a number of hypotheses that could be tested to explain species richness patterns in Eastern Cape grasslands. This thesis is organised so that each main chapter deals with a specific body of theory concerning the explanation of diversity patterns. A detailed description of the study area is provided (Chapter 3), including environmental variation and a description of major vegetation patterns. A summary is provided of grassland plant community patterns, as determined by phytosociological studies in the study area. A multivariate analysis of environmental variables was undertaken to determine which variables contributed the most towards explaining environmental variation in the study area and to determine whether any variables co-vary, a possible problem for any multivariate analysis in later chapters. Altitude produced one of the strongest gradients in the study area. There were a number of variables that were correlated with altitude, most notably temperature. Rainfall co-varied partially with altitude, but there was also a strong rainfall gradient perpendicular to the altitude gradient. A description of species richness, diversity and evenness patterns at the plot scale within different grassland plant communities of the Eastern Cape is provided in Chapter 4. To determine whether the environment acts differently on different growth forms, the contribution to species richness by different major growth forms is analysed. Furthermore, since the majority of literature attempts to explain diversity in terms of environmental factors, it was necessary to analyse the relationship between species richness and various environmental variables. The results indicate that there is high variation in species richness both within and among grassland communities. Forbs make the most significant contribution to overall species richness per 100 m2, followed by grasses. Variance in richness of all species together is not significantly related to environmental variables in mesic grasslands, but is significantly related to environmental variables in semi-arid grasslands. The result of greatest interest from this chapter is the fact that richness amongst different life-forms in the same place is explained by different environmental factors, indicating that the environmental factors that affect coexistence of species have a different effect on different life-forms. A classification of all the species of the dataset into plant functional types using a multivariate approach based on functional traits was conducted (Chapter 5). The grass species were classified into 16 functional types and the forbs into 14 functional types. The functional type classification provided the opportunity for undertaking analyses to develop an understanding of 8 the contribution by niche differentiation towards promoting species richness (Chapter 6). The results provide evidence of niche differentiation in the grasslands of the study area and also that niche differentiation promotes species richness in the grasslands of the study area. It was found that higher rainfall grasslands are less structured by niche differentiation than semi-arid grasslands. A regional / historical analysis is undertaken (Chapter 7) to investigate the relationship between the regional species pool and local richness, and the relationship between local richness and phytochorological diversity. Regional richness appears to have little effect in promoting local richness in grassland plant communities of the study area except at sites where there is high local richness. This provides an indication that regional richness only promotes local richness in the absence of local limiting factors. Phytochorological diversity promotes local richness, but mostly through diversity amongst species with narrow distribution ranges. Some theories ascertain that seasonal uncertainty may provide opportunities to species that would otherwise be outcompeted and thereby promote local richness. The degree to which seasonal uncertainty and seasonality promote local richness in the Eastern Cape grasslands was therefore investigated (Chapter 8). A weak relationship exists between these variables and local species richness in grassland communities of the study area, indicating that they do not promote niche differentiation to a significant degree in the study area. It is clear that in the grasslands of the Eastern Cape, environmental limiting factors are more important in semi-arid grasslands and species interactions are more important in mesic grasslands for structuring plant communities (Chapter 9, Discussion). Regional processes do not appear to be important in structuring local communities, but the analysis undertaken in this study shows that they may be significant when factors operating at the other two levels are overcome (species interactions and environmental limiting factors.
- Full Text:
- Date Issued: 2009
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