PARENT SESSION
Oral Session 142: Mammalian Ecology.
Presiding: S Vignieri and D Berteaux
Friday, August 6, 8:30 AM to 12:00 PM, Meeting Room F 151.
The evolution of mammalian body mass on Santa Cruz Island, California.
Bakker, Victoria*,1, Van Vuren, Dirk1, Garcelon, David2, Crooks, Kevin3, Woodroffe, Rosie1, Aschehoug, Erik4, 1 University of California, Davis, CA2 Institute for Wildlife Studies, Arcata, CA3 Colorado State University, Fort Collins, CO4 The Nature Conservancy, Ventura, CA
ABSTRACT- The evolution of smaller body sizes by large mammals (>100 g) on islands is well documented ("the island rule"). We examined the body masses of two large mammals with disparate evolutionary histories on Santa Cruz Island, California–island spotted skunks (Spilogale gracilis amphiala) and feral sheep (Ovis aries). We also investigated changes in pelage traits, which are under strong selection in both species. The colonization history of skunks is unknown but apparently exceeds 400 years. Sheep inhabited the island for approximately 130 years in a wild or semi-wild state prior to their eradication beginning in 1979. A small sample of island sheep was raised by mainland farmers, allowing examination of environmental influences on body mass. We collected body masses of skunks from live trapped individuals and museum specimens. We obtained sheep body mass data from fresh carcasses of culled island sheep and live weights of farmed sheep. We compared both taxa to body mass data from the literature. Island spotted skunks did not appear smaller than mainland subspecies, presenting an exception to the island rule. In contrast, adult island sheep were significantly smaller than purported founder breeds, suggesting rapid evolution after release from artificial selection. Growth curve models for feral and farm-raised island sheep differed for males only, indicating that males possessed more plasticity in body size, which may result from the alpha male breeding system in wild sheep.
Key words: body size, Ovis aries, island rule, Spilogale gracilis amphiala