The role of local and landscape level factors in determining bumblebee abundance and richness

Abstract

Wild bees are important contributors to the pollination ecosystem service, but they are especially vulnerable to agricultural intensification which causes the loss and fragmentation of natural habitats. We monitored bumblebee populations (Bombus spp.) in 14 grassland patches incorporated into the agricultural habitat mosaic in the Mezőfold region, Hungary. We asked how bumblebee populations were affected by local vegetation quality and the presence of various landscape elements, including fields in agri-environmental schemes, at various spatial scales. A stratified analysis revealed that vegetation quality, especially the lack of weeds, was the most important local factor that positively affected both bumblebee abundance and species number. We found no significant landscape scale effects between 50–250 m. Between 500–1000 m grassland area in the landscape had consistently significant positive effect on species richness. At the 2 km scale the extent of arable fields had a negative impact on both abundance and richness. A higher percentage area of arable fields in the landscape participating in agri-environmental schemes had no positive effect on bumblebee abundance or species richness. Considering all local and landscape effects and their possible interactions, model selection and variance partitioning revealed that local factors were the most important determinants of bumblebee richness and abundance. Local and landscape factors had high shared variance but did not interact with each other. The present study indicated that small scale landscape composition had the lowest importance, but larger scale landscape composition was significant, most likely because bumblebees can forage far from their nests. If we are able to provide good quality grassland patches incorporated into the agricultural habitat mosaic, then we can build on the strong spill over propensity of bumblebees and can expect their contribution to the pollination of various crops.