Diversity and function of leaf litter ants in Colombian coffee agroecosystems.

Abstract

The loss of biodiversity and associated functions in managed ecosystems is one of the most critical issues for conservation because it affects the long-term sustainability of the planet. This dissertation investigates causes and effects of agricultural intensification on the structure and function of ant assemblages in coffee plantations and forest patches of Andean Colombia. Coffee intensification significantly reduced vegetation complexity and increased management index values, as measured from 14 habitat variables. Using a leaf-litter sampling protocol I found that less intensified coffee farms harboured significantly higher ant species richness. Ant communities in polygeneric shaded coffee were significantly more similar to forest patches than any other management type. Additionally, significant positive associations among ant communities and the number of species involved in ant mosaics dropped sharply with intensification. I carried out nesting resource augmentation experiments to examine how the quantity and quality of nesting resources affect ant biodiversity. Ants responded quickly to the addition of nesting resources across the intensification gradient. In the quality resources experiment, the diversity of ants nesting in multi-species groups of twigs was significantly higher than in monoespecific groups across all scales. These results suggest that bottom-up mechanisms are important for ant species loss throughout the technification process although other biotic and abiotic factors such as microhabitat and competition might also play a role. Finally, ant predation in shaded vs. unshaded coffee plantations was studied in the field and laboratory. Exclosure experiments demonstrated that ant communities prey on the coffee berry borer (<italic>Hypothenemus hampei</italic>) in both shaded and unshaded coffee plantations, but this function increased with shade in the wet season, when most infestation takes place. Ants were more effective predators in laboratory conditions than in the field. Predation in the field fluctuated between 2%--27% of borer adults. My studies strongly support the conclusion that the structure and function of ant biodiversity are negatively affected by intensification of coffee agriculture. I recommend that immediate action be taken to stop the destruction of traditional coffee practices and prevent further biodiversity loss in hotspots of tropical biodiversity.