The effect of temporal resource availability on bee diversity and pollination services in a coffee agroecosystem
With current trends of bee declines, the importance of bee conservation research cannot be overstated. A major contributor to declines is habitat destruction, which maintains necessary floral resources for nesting and foraging. Insights into how spatial availability of these resources influences bees is beginning to be understood, but the effects of temporal variability of resources throughout the year on bees is much less studied. This is particularly relevant in the tropics, where the foraging season extends throughout the entire year. Much of the tropical landscape is dominated by agriculture, a dominant crop being coffee. This study seeks to understand the potential for coffee landscapes to support bee diversity. Coffee is particularly relevant as it is naturally grown under shade trees, which offer important resources for bees at various times throughout the year. The following questions were tested: 1.) What better explains bee diversity at a certain time, present resource availability, or consistency in temporal resource availability at that site and is there an interaction between them? 2.) Do sites with greater consistency in temporal resource availability have increased stability in pollination services? Four treatments, with varying availability of floral resources, from always having floral resources to never having floral resources, were examined in a coffee plantation in Southern Mexico. Sites were sampled for bees 2 times during the rainy season and 2 times during the dry season, including when coffee was flowering. Additionally, exclosures were installed on coffee bushes prior to coffee flowering in order to measure the effect of bee pollination on fruit set.
Abundance of bees varied with the percentage of trees in flower and percentage of ground cover in flower at each site throughout the year. The number of individuals of Inga micheliana, a dominant shade tree, was correlated with bee abundance when it is not in flower, but not when it is in flower in the dry season. The number of coffee bushes per site was positively correlated with bee diversity and abundance. These preliminary results indicate that management of coffee with a greater number and diversity of shade trees with flowers, as well as maintaining herbaceous ground cover, is beneficial for bee conservation. Similarly, diversity of bees pollinating coffee have been previously found to increase fruit weight and thus yield; these results may suggest greater stability in pollination services by bees and increases in coffee yields with greater temporal consistency in floral resources.