MSc (Botany) / Department of Botany / The overall aim of this study was to determine the population biology of Sclerocarya birrea (A Rich) Hochst., subspecies caffra (Sond) at Nylsvley Nature Reserve, Limpopo, South Africa. Sclerocarya birrea is a keystone plant species which is rated as one of the most highly valued indigenous trees because of its multiple uses. It is identified as a key species to support the livelihood of rural communities and it is central to various commercial activities. Sclerocarya birrea is also widely used by game in protected areas and by humans in communal areas for its fruit, wood and medicinal properties. Understanding the population biology for this key stone species is important as there are many environmental factors that are affecting its population structure. The study found that the population of S. birrea at Nylsvley Nature Reserve is fairly healthy and is mainly comprised of seedling and adult trees. Evidence of predators feeding on the seeds of Sclerocarya birrea was also recorded in this study. Additionally, disturbance, such as fire and cutting do not have negative impact on S.barrea

In South Africa, the unsustainable use of natural resources by domestic livestock has led to resource depletion and serious land degradation. Rangeland degradation, especially bush encroachment and soil erosion, is particularly acute in the North-West Province, where all districts show signs of desertification and a loss of biodiversity resulting in a deterioration of human and animal health. This has a major impact on livestock productivity and the economic viability of livestock farming with serious consequences for the livelihoods of pastoral communities. It is important to recognise ecological change before irreversible changes occur. The aim of this study, which falls within the Global Environmental Facility Desert Margins Programme (GEF-DMP), was to investigate to what extent vegetation in combination with ant communities can be used as indicators of ecosystem change due to anthropogenic human induced land-use patterns and how can this information be used in land degradation management and biodiversity conservation in the semi-arid western rangelands of Southern Africa. Sites, representing a degradation gradient (relative poor and relative good rangeland condition extremes) within each of three Tribal-, three Commercial- and three Reserve areas, were surveyed. The impacts of these land uses on the herbaceous species composition, woody-, soil- and ant components were evaluated. Both the woody and herbaceous species components reflected the existence of a rangeland condition/degradation gradient across the larger study area. The herbaceous species composition reflected similar degradation tendencies within the Commercial and Reserve land uses, with sites being associated with low rangeland as well as high rangeland condition scores. The tendencies differed between these two land uses based on the woody degradation gradient. The entire Tribal herbaceous- and woody species components showed a transitional shift towards another state, which differed significantly from the Commercial and Reserve land uses. Both the Tribal herbaceous and woody components were associated with low to intermediate rangeland condition ranges, with no significant rangeland condition gradient existing within the Tribal land use. Understanding and quantification of the soil-vegetation dynamics hold important implications for rangeland degradation management. This study provided criteria for selecting the most appropriate measures when incorporating the soil parameters as additive data in the multivariate analyses with the vegetation, ant and nominal environmental data. Different land use practices resulted in different soil patterns, with significant gradients pertaining to the soil stratum and openness/woodiness groups. There was a significant though neglectable difference pertaining to the rangeland condition/degradation gradient based on the soil component. Ants have been extensively used as bio-indicators, also with regard to the monitoring of the environmental effects of rangeland pastoralism. Ant species compositional patterns and functional groups displayed congruent clustering and diversity patterns as those of the vegetation and soil components. In contrast to the vegetation components, ant assemblages did not reflect a degradation gradient, but rather reflected environmental changes (modifications) to the habitat structure and - heterogeneity as a result of different land use disturbances. Both vegetation and ant diversity measures were mainly associated with the Tribal land use. These diversity indices were indicators of habitat complexity, heterogeneity and moderate disturbance, rather than indicators of a rangeland condition/degradation gradient. The diversity patterns are best described by a dichotomy between the humped-shaped productivity/diversity and the habitat complexity/heterogeneity models. Vegetation and ant diversity measures for this study should be considered as environmental indicators of habitat disturbance rather than as biodiversity indicators. It is suggested that vegetation, soil and ant patterns are best described by the state-and-transition model, which encompasses both equilibrium and non-equilibrium systems. The resilient nature of these rangelands, typical of non-equilibrium systems, was reflected by the low to intermediate differences between land uses with regard to the herbaceous, woody, soil and ant components. However, densitydependent coupling of herbivores to key resources resulted in transitional shifts and modification of the vegetation composition and structure within and between land uses, displaying the equilibrium dynamics pertaining to these rangelands. Small disturbances in these rangelands may result in detrimental “snowball” interactive biotic-biotic /abiotic cascades. Spatial heterogeneous patterns within and between land uses as displayed by the vegetation, soil and ant parameters, necessitate that monitoring and management at patch, paddock and landscape scale should be conducted, cautioning against the extrapolation and over simplification of management strategies across all land uses. Because these arid rangelands are linked socio-ecological systems, it is not possible to address biophysical issues associated with land degradation without including the human dimensions. A “Key assessment matrix” is provided for monitoring and management purposes pertaining to land degradation and diversity aspects within and between the different land uses, and can be used by the land user, extension officer and scientist. / Thesis (Ph.D. (Botany))--North-West University, Potchefstroom Campus, 2007.

In South Africa, the unsustainable use of natural resources by domestic livestock has led to resource depletion and serious land degradation. Rangeland degradation, especially bush encroachment and soil erosion, is particularly acute in the North-West Province, where all districts show signs of desertification and a loss of biodiversity resulting in a deterioration of human and animal health. This has a major impact on livestock productivity and the economic viability of livestock farming with serious consequences for the livelihoods of pastoral communities. It is important to recognise ecological change before irreversible changes occur. The aim of this study, which falls within the Global Environmental Facility Desert Margins Programme (GEF-DMP), was to investigate to what extent vegetation in combination with ant communities can be used as indicators of ecosystem change due to anthropogenic human induced land-use patterns and how can this information be used in land degradation management and biodiversity conservation in the semi-arid western rangelands of Southern Africa. Sites, representing a degradation gradient (relative poor and relative good rangeland condition extremes) within each of three Tribal-, three Commercial- and three Reserve areas, were surveyed. The impacts of these land uses on the herbaceous species composition, woody-, soil- and ant components were evaluated. Both the woody and herbaceous species components reflected the existence of a rangeland condition/degradation gradient across the larger study area. The herbaceous species composition reflected similar degradation tendencies within the Commercial and Reserve land uses, with sites being associated with low rangeland as well as high rangeland condition scores. The tendencies differed between these two land uses based on the woody degradation gradient. The entire Tribal herbaceous- and woody species components showed a transitional shift towards another state, which differed significantly from the Commercial and Reserve land uses. Both the Tribal herbaceous and woody components were associated with low to intermediate rangeland condition ranges, with no significant rangeland condition gradient existing within the Tribal land use. Understanding and quantification of the soil-vegetation dynamics hold important implications for rangeland degradation management. This study provided criteria for selecting the most appropriate measures when incorporating the soil parameters as additive data in the multivariate analyses with the vegetation, ant and nominal environmental data. Different land use practices resulted in different soil patterns, with significant gradients pertaining to the soil stratum and openness/woodiness groups. There was a significant though neglectable difference pertaining to the rangeland condition/degradation gradient based on the soil component. Ants have been extensively used as bio-indicators, also with regard to the monitoring of the environmental effects of rangeland pastoralism. Ant species compositional patterns and functional groups displayed congruent clustering and diversity patterns as those of the vegetation and soil components. In contrast to the vegetation components, ant assemblages did not reflect a degradation gradient, but rather reflected environmental changes (modifications) to the habitat structure and - heterogeneity as a result of different land use disturbances. Both vegetation and ant diversity measures were mainly associated with the Tribal land use. These diversity indices were indicators of habitat complexity, heterogeneity and moderate disturbance, rather than indicators of a rangeland condition/degradation gradient. The diversity patterns are best described by a dichotomy between the humped-shaped productivity/diversity and the habitat complexity/heterogeneity models. Vegetation and ant diversity measures for this study should be considered as environmental indicators of habitat disturbance rather than as biodiversity indicators. It is suggested that vegetation, soil and ant patterns are best described by the state-and-transition model, which encompasses both equilibrium and non-equilibrium systems. The resilient nature of these rangelands, typical of non-equilibrium systems, was reflected by the low to intermediate differences between land uses with regard to the herbaceous, woody, soil and ant components. However, densitydependent coupling of herbivores to key resources resulted in transitional shifts and modification of the vegetation composition and structure within and between land uses, displaying the equilibrium dynamics pertaining to these rangelands. Small disturbances in these rangelands may result in detrimental “snowball” interactive biotic-biotic /abiotic cascades. Spatial heterogeneous patterns within and between land uses as displayed by the vegetation, soil and ant parameters, necessitate that monitoring and management at patch, paddock and landscape scale should be conducted, cautioning against the extrapolation and over simplification of management strategies across all land uses. Because these arid rangelands are linked socio-ecological systems, it is not possible to address biophysical issues associated with land degradation without including the human dimensions. A “Key assessment matrix” is provided for monitoring and management purposes pertaining to land degradation and diversity aspects within and between the different land uses, and can be used by the land user, extension officer and scientist. / Thesis (Ph.D. (Botany))--North-West University, Potchefstroom Campus, 2007.

Made available in DSpace on 2016-06-02T19:32:01Z (GMT). No. of bitstreams: 1 4244.pdf: 1071959 bytes, checksum: 6ba82849d82a8316bf2d47e4273770cb (MD5) Previous issue date: 2011-03-02 / Euterpe edulis is a very important palm tree from the Brazilian Atlantic Forest due to its ecological and economic role. However, due to the indiscriminate overexploitation its populations has been reducing greatly. This study aimed to characterize the conservation status of a E. edulis population in a fragment of Atlantic Forest at Southern Bahia. We monitored this population along 5 running years in a 0.8 hectare. Environmental variables were also collected to test which factors could affect plant development and projection matrices analysis were performed to estimate the population growth rate and sensibility. The results showed that population s density is lower if compared with others studies. We verified a decrease in the seedling s recruitment over years, which were attributed to fragmentation side-effects, such as microclimate changes and / or reproductive isolation or inbreeding depression. We also observed that the low rate of transition from stages 1 to 2, represents a bottleneck for the population growth. These results emphasize the urgency of more long-term studies on the population ecology and genetic of E. edulis and also management strategies to promote the sustainability of such natural populations. / Euterpe edulis é uma das espécies de maior importância ecológica e econômica na Mata Atlântica brasileira. Apesar de a espécie possuir características que favorecem o manejo sustentável, a exploração predatória gerou um cenário de populações naturais severamente reduzidas. Este estudo procurou caracterizar o atual estado de conservação de uma população no sul da Bahia. Para tanto foi definido um bloco amostral 0,8 hectare, onde foi monitorada uma população de E. edulis, dividida em seis estágios de desenvolvimento. Foram geradas matrizes de projeção para verificar a tendência atual de conservação da população e variáveis ambientais foram analisadas para inferir sobre como tais fatores podem afetar o desenvolvimento da espécie. Os resultados mostraram que a densidade da população encontrada nesse estudo é menor que a relatada em outros estudos já realizados com a espécie. Verificou-se também a diminuição abrupta no recrutamento de plântulas a cada ano, o que foi atribuído a algum efeito colateral da fragmentação florestal, tal como alterações microclimáticas, e/ou efeitos do isolamento reprodutivo, como a depressão endogâmica. A lenta transição do estágio jovens 1 para jovens 2 se mostrou como principal gargalo ao crescimento populacional, o que sugere a necessidade de estudos sobre a redução na fecundidade. Ambientes com maior homogeneidade de dossel propiciaram maior crescimentos em jovens 2. Propõe-se que a produção e manutenção de mudas em viveiros até a idade de um ano, seguida de plantio em áreas próximas às bordas de clareiras, possa diminuir a mortalidade dos estágios iniciais e garantir maior êxito na perpetuação das populações de Euterpe edulis no sul da Bahia.

Submitted by FABIANA DA SILVA FRANÇA (fabiana21franca@gmail.com) on 2018-02-23T17:33:04Z No. of bitstreams: 1 Arquivo Total.pdf: 2718770 bytes, checksum: 9378d34888dfcacdd356cf58ac71eaa8 (MD5) / Made available in DSpace on 2018-02-23T17:33:04Z (GMT). No. of bitstreams: 1 Arquivo Total.pdf: 2718770 bytes, checksum: 9378d34888dfcacdd356cf58ac71eaa8 (MD5) Previous issue date: 2017-03-22 / The Rufford Foundation / Understanding the ecological role of species within an ecosystem depends largely on knowledge of its trophic relations. Such relations and the position of species within a foodweb are a central step in understanding the dynamics of the communities and the impacts that each species has on the trophic network compartments. The knowledge on the diet of the South American freshwater stingrays has increased considerably over the last years,but still, little is know about their ecological role. Thereby, the aim of this research is to evaluate the importance of the stingray Potamotrygon magdalenae in the structure of a freshwater food web. The feeding habits and the trophic ecology of this species were evaluated using stomach content analysis in combination with stable isotopes of carbon and nitrogen from samples collected in the middle Magdalena river basin, Colombia, and its ecological importance from topological analyzes of trophic networks. Potamotrygon magdalenae showed a specialized diet, feeding primarily on insects. No significant differences of δ13C and δ15N were observed in the muscle of the species between the hydrological periods of high and low waters. The species isotopic niche was intermediate. In terms of ecological importance, it played an intermediary role in the dispersion of indirect effects through the system, due to its intermediate values of centrality and topological importance. These results provide a starting point for further ecological studies about the South American freshwater stingray species, in order to assess their role in the ecosystem. On the other hand, theycomplement the existing studies of Potamotrygon magdalenae. / Compreender o papel ecológico das espécies no ecossistema depende amplamente do conhecimento de suas relações tróficas. Conhecer tais relações e a posição das espécies em umarede é um passo crucial para entender a dinâmica das comunidades e os impactos quecada espécie tem sobre os demais compartimentos. Oconhecimento sobre adieta das espécies de raias de água doce de América do Sul tem aumentado consideravelmente ao longo dos últimos anos, porém, é muito pouco o que se sabe sobre o papel ecológico das espécies nos seus respectivos ecossistemas. Assim, oobjetivo deste trabalho foi avaliar a importânciaecológica da raia Potamotrygon magdalenae na estrutura da rede trófica de um ecossistema de águas continentais. Foram avaliados os hábitos alimentares e a ecologia trófica da espécie através da análise de conteúdos estomacais e isótopos estáveis de carbono e nitrogênio a partir de amostras coletadas na bacia do médio rio Magdalena, Colômbia; e sua importância ecológica a partir de análises topológicas de redes tróficas. A espécie foi considerada um predador especialista de nível trófico intermediário, com preferência pelos insetos.Não foram observadas diferenças significativas de δ13C e δ15N na espécie entre os períodos hidrológicos de cheia e de águas baixas. O seu nicho isotópico foi intermediário. Em relação à importância ecológica, a espécie desempenhou um papel intermediário na dispersão de efeitos indiretos através do sistema, devido aos seus valores intermediários de centralidade e importância topológica. Estes resultadosconstituem um ponto de partida para novos estudos ecológicos das espécies de raias de água doce da América do Sul, que visem avaliar seu papel nos ecossistemas, e complementam os estudos existentes de Potamotrygon magdalenae.

Made available in DSpace on 2014-07-29T16:21:22Z (GMT). No. of bitstreams: 1 Dissertacao Ronny Jose de Morais.pdf: 2115544 bytes, checksum: 03e8e5ddfa9ad11a524561cb60350796 (MD5) Previous issue date: 2010-03-25 / In this study trophic interactions and flows of energy/matter of three lagoons in the Pantanal (MS) submitted to the annual flood pulse - Baia da Onça, Braço Morto Acima and Braço Morto Abaixo - were analyzed with models of mass balance constructed using the Ecopath software. Thus, the objectives were: (i) to describe the mechanisms that control the dynamics of trophic webs, (ii) to identify the major groups that act as keystone, (iii) to identify information gaps for these environments, (iv) to quantify the ecotrophic community and assess the degree of development of the ecosystem. In addition to several fish compartments in other groups were inserted to compose the models, such as phytoplankton, macrophytes, zooplankton, aquatic insects, terrestrial insects, birds, reptiles and mammals. The data from fish compartments were collected in 1988-1990 and the other compartments were taken from literature. To identify the groups that act as keystone an index that is based on the trophic impact matrix of each model was used. The results indicate that in the three models, biomass and number of species concentrated between trophic levels 2 and 3, suggesting that within these levels there is greater stability, allowing the coexistence of species. In the three models, the most effective contribution of the energy flow is observed from the detritus compartment to the trophic level II, highlighting the role of detritivores in the systems. The trophic impact matrix obtained for the three models confirms the participation of detritus and some compartments found in lower trophic levels (aquatic insects and zooplankton) over most of the groups in the models, suggesting a bottom up control system. However, the presence of top predators and their strong relationships with other groups suggest the presence of top-down effect. This is verified by analysis of the index of keystone, which in the three models is greater for detritus, Hoplias malabaricus, Serrasalmus spp, birds and mammals. So, there are in the three lagoons a matched control (bottom-up and top-down) with the acting of primary producers and higher trophic levels. The analysis of some ecosystem attributes, such as PP/R, Ascendency, Overhead and Ratio Schödinger show that the three systems are mature and have high resilience. This study is considered an initial step in the synthesis of ecological interactions about the Pantanal lagoons (MS) for that there are no studies with this approach to this ecosystem. / Neste trabalho, as interações tróficas e os fluxos de energia/matéria de três lagoas marginais do Pantanal (MS) submetidas ao pulso de inundação anual - Baía da Onça, Braço Morto Acima e Braço Morto Abaixo - foram analisados com modelos de balanço de massas elaborados no software Ecopath. Assim, os objetivos foram: (i) descrever os mecanismos que controlam a dinâmica das teias tróficas; (ii) identificar os principais grupos que atuam como espécie-chave; (iii) identificar as lacunas de informação para estes ambientes; (iv) quantificar a comunidade ecotrófica e avaliar o grau de desenvolvimento do ecossistema. Além dos diversos compartimentos peixes, foram inseridos outros grupos para compor os modelos, como fitoplâncton, macrófitas, zooplâncton, insetos aquáticos, insetos terrestres, aves, répteis e mamíferos. Os dados dos compartimentos peixes foram coletados em 1988-1990 e dos outros compartimentos foram retirados da literatura. Para identificar os grupos que atuam como espécie-chave foi utilizado um índice que se baseia na matriz de impacto trófico de cada modelo. Os resultados indicam que nos três modelos, a biomassa e o número de espécies concentrou-se entre os níveis tróficos 2 e 3, sugerindo que dentro destes níveis ocorre uma maior estabilidade, o que permite a coexistência de espécies. Nos três modelos a contribuição mais efetiva do fluxo de energia é observada do compartimento de detritos para o nível trófico II, evidenciando o papel da detritivoria nos sistemas. A matriz de impacto trófico obtida para os três modelos corrobora a participação dos detritos e de alguns compartimentos presentes em níveis tróficos inferiores (insetos aquáticos e zooplâncton) sobre a maioria dos grupos nos modelos, sugerindo um controle bottom-up no sistema. No entanto, a presença de predadores de topo e suas fortes relações com os demais grupos sugerem ainda a presença do efeito top-down. Isto é verificado pela análise do índice de espécie-chave, que nos três modelos é maior para detritos, Hoplias malabaricus, Serrasalmus spp, aves e mamíferos. Portanto, há nas três lagoas um controle combinado (bottom-up e top-down) com a atuação dos produtores primários e dos níveis tróficos superiores. A análise de alguns atributos ecossistêmicos, como PP/R, Ascendência, Overhead e Razão de Schödinger mostram que os três sistemas são maduros e possuem alta resiliência. Este estudo é considerado um passo inicial na síntese das interações ecológicas sobre as lagoas marginais do Pantanal (MS) haja vista que não há trabalhos com esta abordagem para este ecossistema.