Bates observed that many Heliconid species are accompanied by other species (Pierids), which mimic them, and often cannot be distinguished from them in flight. They fly in the same parts of the forest as the model (Heliconid) and often in company with them. Local races of the model are accompanied by corresponding races or species of the mimic. So a scarce, edible species takes on the appearance of an abundant, noxious species. Predators, Bates supposed, learn to avoid the noxious species, and a degree of protection covers the edible species, no doubt proportional to its degree of likeness to the model. These testable hypotheses about warning signals and mimicry helped to create the field of evolutionary ecology.