The Diversity and Ecology of Spiders in Coffee Agroecosystems in the Soconusco Region, Chiapas, Mexico.

Agricultural landscapes are globally distributed and can function as refuges for biodiversity. My research focuses on elucidating the factors that influence predators and their ecological interactions in agricultural landscapes. I studied patterns of richness and abundance of a predator group, spiders, to understand its response to local factors (agricultural management, presence of aggressive ants) and landscape factors (distance to forest) in a coffee landscape composed of forest remnants (6%) and coffee farms (94%). First, I examined the patterns of ground dwelling spider diversity associated with coffee management intensification as well as the response of spider diversity to canopy cover, slope of the terrain, litter biomass, and distance to forest. Findings show that local spider richness and abundance were generally higher in simplified agroecosystems. Distance to forest had a mild correlation with spider abundance; in contrast local spider richness and abundance had a strong negative correlation with slope. Second, I examined the response of tree-trunk dwelling spider diversity and biomass to Azteca instabilis ants, tree characteristics, canopy cover and distance to forest. Results show that local spider richness was positively correlated with tree diameter, whereas spider abundance and biomass were positively correlated with tree diameter, and A. instabilis. Third, I examined spiders in coffee plants and their response to A. instabilis in contrasting coffee agroecosystems. Results show that spider richness and abundance were higher in the intensified sites and in the presence of A. instabilis. Potential mechanisms for the spider-ant association were prey availability and protection against predators. Fourth, I examined the abundance of the most abundant spider genus in coffee plants, Pocobletus, in relation to coffee branchiness and ants presence. Results show that Pocobletus is positively associated with coffee branchiness and the presence of A. instabilis and P. synanthropica ants. Evidence suggested that the positive association Pocobletus-ants was due to prey abundance and enemy-free space. In sum, ground and coffee dwelling spiders were locally more diverse and abundant in the intensified agroecosystems, whereas tree-trunk dwelling spiders were more sensitive to coffee intensification. Spiders were positively associated with aggressive ants. Distance to forest was not an important predictor of spider diversity.PhDNatural Resources and EnvironmentUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102421/1/lmarin_1.pd