From Nature:
Ecologists are divided over whether the predators inhabiting an ecosystem are a good guide to its total biodiversity. The debate may lead conservationists to reassess how they prioritize their efforts and design nature reserves.
Conservationists have long sought groups of species whose diversity reflects the total biodiversity in an area. Such indicators can help identify the places most in need of protection.
Based on their analyses of birds of prey, Fabrizio Sergio, at the Doñana Biological Research Station in Spain, and his colleagues have argued that top predators could be just such indicators. Working in the Italian Alps, they have found that the number of birds of prey in a place is a good reflection of other species living there.
More here.