 As with any predator at or near the top of its food chain , the cougar impacts the population of prey species . <unk> by cougars has been linked to changes in the species mix of deer in a region . For example , a study in British Columbia observed that the population of mule deer , a favored cougar prey , was declining while the population of the less frequently preyed @-@ upon white @-@ tailed deer was increasing . The Vancouver Island <unk> , an endangered species endemic to one region of dense cougar population , has seen decreased numbers due to cougar and gray wolf predation . Nevertheless , there is a measurable effect on the quality of deer populations by puma predation . 
