Landscape management can foster pollinator richness in fragmented high-value habitats

Pollinator diversity is declining due to habitat loss, low habitat quality, limited habitat connectivity and intensification of agriculture in remaining high-value habitats within human-dominated landscapes, such as calcareous grasslands. Options to increase the local area of protected habitats are often limited. Therefore, we asked how local habitat quality as well as agri-environmental schemes (AES) and configuration of the surrounding landscape can contribute to the preservation of pollinator diversity. We sampled bees, butterflies and hoverflies in 40 calcareous grasslands in Germany, and assessed the effects of calcareous grassland area, quality and connectivity, agricultural configuration, and AES on species richness and abundance. While calcareous grassland area was an important predictor for bee and butterfly species richness, with strongest effects sizes for endangered species, local flower resources and nesting sites and landscape characteristics such as small field size, high proportion of organic fields and connectivity with other grasslands significantly enhanced pollinator richness with responses differing among the three studied taxa. In contrast to expectations, AES flowering fields did not benefit pollinator communities in grasslands. We conclude that improving local habitat quality in combination with targeted landscape management are effective measures to promote pollinator richness in highly fragmented protected grassland.