Biological indicators measure components of the biota and are used to give general information about complex ecosystems in which they occur, playing key roles in conservation planning and management. This study illustrates the impact of habitat change by factors that are extrinsic to the habitats in question and the importance of spider responses in aiding management decisions. The spider responses illustrated existence of environmental change and represent responses of other biota. The conclusions drawn from this study have important management implications for protected areas with grazing herbivores and occurrence of alien invasive plants. Grazed sites showed the highest abundance, diversity and species richness, while ungrazed had the lowest. The implications from this study are that no grazing has negative implications on lower trophic levels, whereas grazing seems to result in favourable conditions for optimal abundance, diversity and species richness. The higher abundance, diversity and species richness associated with grazed sites could result from increased ground cover, greater variation in habitat structure, increased plant diversity and enhanced soil/plant nutrient concentrations. But, ungrazed sites in turn become more monotonous and provide less habitat diversity. However, the characteristic species for each grazing intensity level demonstrates the difficulty in making generalizations for management even for closely related species. The results further opposed the assumption that grazing lawns are a result of overgrazing and thus highly undesirable. This grassland type in comparison to tall bunch grassland displayed the highest spider diversity and species richness. This evidence further supports the conclusion that grazing lawns are steady state communities of their own and not a sub-set of any other grassland type. Therefore, veld management decisions that eradicate grazing lawns are negative for the park as the fauna and flora associated with this grassland type will be lost, leading to cascading effects. Additionally, this study illustrated that habitat modification by invasion of invasive alien plant species has detrimental consequences for the endemic fauna. C. odorata invasion results in a monotonous habitat structure. Consequently, structural heterogeneity is a primary determinant for spider diversity as opposed to abundance of prey, because plant height and architecture drive spider colonization. Therefore, removal of alien invasive weeds results in returning a system to close approximation of its condition prior to disturbance with both structure and function recreated. Assemblage patterns can be selected as endpoints to measure the ecological rehabilitation; thus, the non-significant differences in assemblage patterns of the control versus cleared sites imply that the system is rehabilitating with clearing without further management intervention. This study adds to the limited information on the implications of grazing intensities, grassland types, short and long-term invasion and clearing of an alien invasive plant on spider communities. Copyright / Dissertation (MSc)--University of Pretoria, 2008. / Animal and Wildlife Sciences / unrestricted

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / For the sustainability of integrated crop-livestock systems, the proper management of its components (soil-plant-animal), which are dynamic and interact with each other, are essential to define the system's ability to provide positive or negative carbon balance to system and determine the physical, chemical and biological soil, which can affect the production capacity of agricultural soils. The objective of this study was to characterize the spatial and temporal variability of soybean yield and understand their relationship with the spatial variability of dungs, physical properties and chemical soil, and soil quality in different grazing intensities in integrated crop-livestock system. Chapter I concluded that the soil organic C stocks under different grazing intensities was related to indices of soil quality. The highest C stratification ratio and C pool index were found in the treatment with moderate grazing intensity. The integrated crop livestock system acts as source or sink of atmospheric C depending on the grazing intensity. Under heavy grazing intensity, the system acts as a source (0.04 Mg ha−1yr−1), and under light grazing intensity, it acts as a sink. The value range from 0.25 to 0.37 Mg ha−1yr−1.Pastures managed at 0.20 and 0.40 m sward height had the best balance between CMI and animal daily weight gain. The best balance between C management index and live weight gain per unit area, C management index and economic return, occurred in sward height of 0.20 m. Chapter 2 concluded that the dung supply affects the cycling of the nutrients P and K in the soil, in comparison with sites without supply, and the pasture height of 10 cm treatment had the highest P content in the soil in relation to the treatment of 0.40 m. The average diameter of the aggregates was higher with 0.40 m in relation to the treatment of 0.10 m and soil density was similar between the heights of the pasture. Treatment of sward height 0.10 m, which had a more homogeneous distribution of dungs in the area, showed greater variability of nutrients P and K, and the treatment of 0.40 m, which had the lowest number of dungs with distribution concentrated in attractive points, had the lowest variability of nutrients. In years with severe water restriction, all pasture height treatments were affected, with an average yield reduced by 80% over 2012/13 and 2013/14 crops without water restriction. The main components affected by water stress were the number of pods per plant and the weight of 1000 grains (2011/12). For the year severe water restriction the sward height of 0.40 m treatment, which provided greater coverage contribution dead on the ground, had the highest soybean yield variability. / Para a sustentabilidade dos sistemas de integração lavoura-pecuária, o manejo adequado de seus componentes (solo-planta-animal), que são dinâmicos e interagem entre si, são fundamentais para definir a capacidade do sistema em prover balanço positivo ou negativo de carbono ao sistema, assim como determinar as mudanças físicas, químicas e biológicas do solo, o que pode afetar a capacidade de produção dos solos agrícolas. O objetivo deste trabalho foi caracterizar a variabilidade espacial e temporal da produtividade da soja e compreender sua relação com a variabilidade espacial das placas de esterco, atributos físicos e químicos do solo, e a qualidade do solo em diferentes intensidades de pastejo em sistema de integração lavoura-pecuária. O Capítulo I concluiu que o estoque de carbono no solo sob diferentes intensidades de pastejo foi relacionado aos índices de qualidade do solo. A maior taxa de estratificação do carbono e o maior índice de estoque de carbono foram encontrados para o tratamento com moderada intensidade de pastejo. A integração lavoura-pecuária age como fonte ou como dreno do carbono atmosférico, dependendo da intensidade de pastejo. Sob alta intensidade de pastejo, o sistem age como fonte (0.04 Mg ha-1 ano-1), e sob baixas intensidades de pastejo como dreno, variando de 0.25 to 0.37 Mg ha-1 ano-1. Pastos manejados com altura de pasto 20 e 40 cm possuem o melhor balanço entre o índice de manejo do solo e o ganho de peso diário. O melhor balanço entre o índice de manejo do solo e o ganho de peso por animal por unidade de área e o retorno econômico ocorreu no tratamento 20 cm. Já o Capítulo 2 concluiu que a presença de placas de esterco afetou a ciclagem dos nutrientes P e K no solo em relação a locais sem esterco na pastagem. O tratamento de altura do pasto de 0,10 m apresentou o maior teor de P no solo em relação ao tratamento de 0,40 m. O diâmetro médio ponderado dos agregados foi maior no tratamento de 0,40 m em relação ao tratamento de 0,10 m e a densidade do solo foi semelhante entre as alturas do pasto. O tratamento de altura do pasto 0,10 m, que possuía uma distribuição mais homogênea de placas de esterco na área, apresentou maior variabilidade dos nutrientes P e K, e o tratamento de 0,40 m, que possuía o menor número de placas de esterco com distribuição concentrada em pontos atrativos, apresentou a menor variabilidade dos nutrientes. Em anos com restrição hídrica severa todos os tratamentos de altura do pasto foram afetados, sendo a produtividade média reduzida em 80% em relação as safras 2012/13 e 2013/14 sem restrição hídrica. Os principais componentes afetados pelo estresse hídrico foram o número de legumes por planta e o peso de 1000 grãos (safra 2011/12). No ano com restrição hídrica severa o tratamento de altura do pasto de 0,40 m, que proporcionou maior aporte de cobertura morta sobre o solo, apresentou a maior variabilidade de produtividade de soja.