Resumo:
Questions about how landscape changes affect biodiversity were investigated in the project "Biogeography, forest fragmentation and extinction thresholds: a multi-taxon study in the Atlantic Rainforest of Bahia, Brazil." As part of this project, in this thesis we examine how habitat reduction affects the diversity of flower visiting bees and the structure of plant-pollinator networks. Pollination is a major ecological process deforestation and agricultural intensification. However, there is a lack of empirical evidence that analyzed these effects. This work encompasses three chapters. In the first chapter we review the literature on the effects of natural landscape changes and agricultural intensification on plants, pollinators and plant-pollinator networks. We have seen that changes in landscapes decrease the diversity and availability of pollinators, affect cross-pollination and sexual reproduction of plants. These effects occur, mainly, because habitat isolation and reduction of floral resources and nesting areas. Approximately 50% of the 155 analyzed studies showed negative effects of agricultural intensification, with conversion of natural areas into agricultural uses. We found one study that discussed these effects for plant-pollinator networks. So, there is a gap in knowledge about the effects of changes in landscapes on plant-pollinator networks. In the second chapter we evaluate how habitat loss affects pollinator diversity in the understory of the Atlantic Forest in Bahia. Bees are the main pollinators of flowering plants in the world and are sensitive to changes in the natural habitat. Our results Show that landscapes with a higher proportion of forest are important to bees, even when the forest is highly fragmented. In the third chapter we question how habitat loss affects the structure of plant-pollinator networks in the understory of the Atlantic Rainforest in Bahia. We observed that in less forested landscapes networks are smaller, have fewer species and are more connected and nested, i.e. have more generalist species interacting with each other in a cohesive core, and there are few specialist species interacting with generalists in these networks. We believe that, due to environmental degradation, generalist flower visitor species are better able to remain in the landscapes, maintaining the networks and also the plant populations. In conclusion, studies on interaction networks from the perspective of the landscape and tropical forests can provide important insights for the conservation of plants, pollinators and pollination. Forest habitats are importante for maintaining the diversity of bees, plant-bee networks, and pollination services.
