BRITT, E.J.*; HICKS, J.W.; BENNETT, A.F.; University of California, Irvine; University of California, Irvine; University of California, Irvine: The energetic consequences of prey specialist and generalist populations of three species of garter snake (Thamnophis elegans, T. couchii and T. ordinoides).

North American garter snakes (Thamnophis spp.) represent a unique study system because of their diverse diets and habitats, both within and among species. For example, the Western Terrestrial garter snake, T. elegans, exists in two geographically isolated populations in northern California: a coastal population with a specialized diet of slugs and an inland population with a generalized diet of fish, anurans, mice and leeches. The difference in prey preferences between the two populations is congenital, heritable, and ontogenetically stable. To test whether or not the coastal slug eaters have an energetic advantage over the inland generalists when digesting slugs, we have shown that the snakes from the specialized coastal populations assimilate more energy from a slug diet than do the generalist snakes. Recently, we have included an interspecific comparison between garter snake species considered to be dietary specialists on slugs (T. ordinoides) and fish (T. couchii). We have designed similar feeding experiments with these species as for the two populations of T. elegans. Using the inland population of T. elegans as the dietary generalist, we tested the hypothesis that dietary specialization of garter snakes is accompanied by increased assimilation efficiency when digesting specialized prey types compared to that of generalist garter snakes. This study was supported by NSF grant IBN 9727762 to A.F.B and J.W.H. and by NSF grant IOB 0445680 to J.W.H.