DISEASE REVEALS THE PREDATOR - SARCOPTIC MANGE, RED FOX PREDATION, AND PREY POPULATIONS

An epizootic of sarcoptic mange was prevalent among Scandinavian red f oxes (Vulpes vulpes) during the late 1970s and 1980s. By substantially reducing the population density of foxes, the epizootic created a nat ural experiment on the importance of fox predation for prey density. T he fox population started to recover during the late 1980s. We monitor ed the populations of the fox and its prey [voles (Cricetidae), mounta in hare (Lepus timidus), European hare (L. europaeus), Capercaillie (T etrao urogallus), Black Grouse (T. tetrix), Hazel Grouse (Bonasa bonas ia), and roe deer (Capreolus capreolus)] throughout the event, on a lo cal (10(1)-10(2) km(2)), a regional (10(4) km(2)), and a national scal e. Methods included den counts, snap-trapping, pellet/dropping counts, counts of displaying birds, young/adult ratio from incidental observa tions of deer, regional questionnaires, and national hunting records. The study revealed red fox predation as a crucial factor in limiting t he numbers of hares and grouse as well as fawns per doe of roe deer in autumn, and in conveying the 3-4 yr cyclic fluctuation pattern of vol es to small game. The classical view, that predators take but a ''doom ed surplus'' of their prey, was false for these species in Scandinavia .