Many, many more pollinators needed Numerous studies have shown that biodiversity is necessary for ecosystem function. The majority of these, however, have taken place at relatively small experimental scales. Winfree et al. looked across more than 3000 square kilometers for relationships between biodiversity and crop pollination (see the Perspective by Kremen). The number of wild bee species required for successful pollination rapidly increased with spatial scale, largely owing to variation in the species present across sites and the degree to which the most abundant species played a role. In the end, more than an order of magnitude more species than predicted by smaller-scale experiments were required for full ecosystem functioning. Science , this issue p. 791 ; see also p. 741