POSITIVE EFFECTS ON GAME SPECIES OF TOP PREDATORS BY CONTROLLING SMALLER PREDATOR POPULATIONS - AN EXAMPLE WITH LYNX, MONGOOSES, AND RABBITS

Top predators have often been persecuted because of their supposed neg ative effects on species of economic concern on which they feed. In so me cases, however, they may actually benefit their prey through intrag uild predation on other smaller predators that share the prey. In each of two representative situations, in one of which lynx were present a nd in the other absent, we (1) estimated gross numbers of rabbits take n by lynx and Egyptian mongooses (smaller predators that are themselve s preyed upon by lynx); (2) simulated size-structured rabbit populatio ns of different densities, taking into account the reproductive value of the individuals taken by predators; and (3) estimated actual rabbit densities. Numbers of rabbits taken by predators during a year were f ound to be between 4.8 and 9.5 times greater when lynx were not presen t. After a year, rabbit population growth for an initial rabbit densit y of 15/ha was between 12% and 22% lower when lynx were not present. F or lower initial rabbit densities, the positive effect of lynx presenc e on rabbits was greater. Actual rabbit densities in the areas used by lynx were 2-4 times higher than in areas not used by lynx, even thoug h these areas were similar or identical in habitat composition. These results support the suggestion that removal of top predators may somet imes have a negative effect on prey populations of human economic conc ern.