Bienen, Wespen und deren Parasitoide in traditionellen Kaffee-Agroforstsystemen: Lebensgemeinschaftsmuster und Ökosystemdienstleistungen

Abstract

In 22 traditional highly diverse coffee agroforests biodiversity patterns at multiple spatial and temporal scales and the importance of biodiversity for ecosystem functioning were analyzed. Additionally an ecosystem service, which is important for humanity, was economically evaluated.In the first part the relation of coffee flower-visiting bees to floral resources at different spatial scales, and the economic value of bee pollination to coffee production were investigated. On a field scale, bee density decreased, with increasing availability of coffee flowers, showing a dilution effect. Conversely on a shrub and on a branch scale bee density increased with increasing availability of floral resources, showing a concentration effect. The results show that bees respond contrastingly to floral resource availability at different spatial scales and indicate that the number of bees available for pollination may be limited at the field scale. Coffee yield (kg/ha) was positively related to the density of coffee flower-visiting bees. Consequently, revenues and net revenues also increased with bee density. Based on these linear relationships it was estimated that yield can increase twofold and net revenues even tenfold with a fivefold increase in bee density. There fore the monetary value of bee pollination for an important cash crop may be emphasised.In the second part seasonal and vertical diversity patterns in solitary hymenoptera and the effect of diversity on an ecosystem function, parasitism, and its temporal stability were analysed by using the community of trap nesting solitary bees and wasps and their parasitoids. Bee species richness was significantly higher at a height of 0.5 m than at 1.5 m, but wasp species richness did not differ between heights. Species number of both solitary bees and wasps was significantly higher in the rainy than in the dry season. The results underline the importance of vertical and seasonal variation in diversity patterns and to differentiate between guilds, as these patterns might be resource generated. Parasitism rates of solitary bees and wasps increased with increasing parasitoid diversity; additionally, wasp parasitism rate decreased with increasing diversity of wasp hosts, thus diversity appeared to provide resistance against consumption. Temporal variability of parasitism rates in bees and wasps decreased with increasing parasitoid diversity, and only for wasps, also decreased with decreasing temporal variability of parasitoid diversity. Thereby evidence is provided that a high and stable parasitoid diversity can enhance and stabilize parasitism rates.To encourage important ecosystem services such as pollination, predation and parasitism, which can be critical for human welfare, a high diversity and abundance of bees, wasps and parasitoids enemies should be conserved. Conservation of nesting sites such as dead wood, large trees or adjacent forest fragments, and food resources, such as a high quantity and quality of flowers can help to maintain a diverse and abundant community of Hymenoptera