BEE DIVERSITY AND SEED SET IN FRAGMENTED HABITATS

Effects of habitat fragmentation on plant-pollinator interactions were studied by analyzing abundance and diversity of bees as well as seed set of two self-incompatible plants on a landscape scale. We experimentally established 40 small patches of Sinapis arvensis and Raphanus sativus at increasing distances from eight species-rich chalk grasslands. Both number and diversity of flower-visiting bees declined for S. arvensis with increasing distance from the nearest chalk grassland whereas the number of visitors belonging to other groups of insects remained constant. Number of seeds per pod as well as pods per plant declined significantly in both species with increasing distance from the nearest chalk grassland. The fruit/flower ratio of R. sativus was halved at a distance of 490 m. Number of seeds per plant was halved at a distance of approximately 1000 m for S. arvensis and at a distance of 260 m for R. sativus. Thus habitat fragmentation affected plant-pollinator interactions at a relatively small scale.