RESOURCE UTILIZATION BY 2 INSULAR ENDEMIC MAMMALIAN CARNIVORES, THE ISLAND FOX AND ISLAND SPOTTED SKUNK

We compared resource utilization of two insular endemic mammalian carn ivores, the island spotted skunk and island fox, along niche dimension s of space, food, and time on Santa Cruz Island. We predicted that res ource use by foxes and skunks would differ along one or more niche dim ensions, and that both species would have broader niches or higher den sities compared with mainland relatives. Island foxes and island spott ed skunks differed to some extent in habitat use, diets, and circadian activity, which may account for their long-term coexistence. Nonethel ess, substantial overlap between skunks and foxes in spatial, dietary, and temporal dimensions suggests that competition between the two spe cies does occur. Moreover, competition may be asymmetric, affecting sk unks more than foxes. Compared with mainland foxes, island foxes have smaller body size, smaller home range, increased population density, i ncreased diurnal activity, and behavior that is more highly inquisitiv e and less flight-prone - all common features of insular faunas. Islan d skunks, however, apparently have not developed these changes, perhap s due to asymmetric competition with foxes in conjunction with severe ecosystem disturbances caused by feral sheep.