Interacting effects of farming practice and landscape context on bumble bees

The populations of farmland birds in Europe declined markedly during the last quarter of the 20th century, representing a severe threat to biodiversity. Here, we assess whether declines in the populations and ranges of farmland birds across Europe reflect differences in agricultural intensity, which arise largely through differences in political history. Population and range changes were modelled in terms of a number of indices of agricultural intensity. Population declines and range contractions were significantly greater in countries with more intensive agriculture, and significantly higher in the European Union (EU) than in former communist countries. Cereal yield alone explained over 30% of the variation in population trends. The results suggest that recent trends in agriculture have had deleterious and measurable effects on bird populations on a continental scale. We predict that the introduction of EU agricultural policies into former communist countries hoping to accede to the EU in the near future will result in significant declines in the important bird populations there.

Ecosystem services are critical to human survival; in selected cases, maintaining these services provides a powerful argument for conserving biodiversity. Yet, the ecological and economic underpinnings of most services are poorly understood, impeding their conservation and management. For centuries, farmers have imported colonies of European honey bees (Apis mellifera) to fields and orchards for pollination services. These colonies are becoming increasingly scarce, however, because of diseases, pesticides, and other impacts. Native bee communities also provide pollination services, but the amount they provide and how this varies with land management practices are unknown. Here, we document the individual species and aggregate community contributions of native bees to crop pollination, on farms that varied both in their proximity to natural habitat and management type (organic versus conventional). On organic farms near natural habitat, we found that native bee communities could provide full pollination services even for a crop with heavy pollination requirements (e.g., watermelon, Citrullus lanatus), without the intervention of managed honey bees. All other farms, however, experienced greatly reduced diversity and abundance of native bees, resulting in insufficient pollination services from native bees alone. We found that diversity was essential for sustaining the service, because of year-to-year variation in community composition. Continued degradation of the agro-natural landscape will destroy this "free" service, but conservation and restoration of bee habitat are potentially viable economic alternatives for reducing dependence on managed honey bees.