A University of California, Davis, scientist has been named a winner of a prestigious Guggenheim Fellowship for 1992. Thomas W. Schoener, a professor of zoology and environmental studies at UC Davis, is among 149 artists, scholars and scientists chosen this year as fellows by the John Simon Guggenheim Memorial Foundation. Fellows are appointed on the basis of unusually distinguished achievement in the past and exceptional promise for future accomplishment. Among his other honors, Schoener, 48, was one of the youngest members accepted into the National Academy of Sciences eight years ago. Schoener will use his award to expand his studies of the ecology of subtropical islands. The award will fund a research expedition this fall to islands off the northeastern coast of Australia, including the Great Barrier Reef. Specifically, Schoener hopes to describe the populations and ecological relationships of birds and lizards, as well as web-weaving spiders and other organisms as time permits. The Australian islands have similar physical characteristics to those of the Caribbean islands that Schoener has been studying for about 15 years. Although the islands' climate, altitude and vegetation height might be similar, scientists do not know if lizards will have as profound an effect on spiders and herbivores in the food web. The Australian island research promises to be a valuable step in extending the knowledge gleaned from the well-studied Bahamas to other ecological systems around the globe. Although Charles Darwin is credited for first focusing biological attention on islands because of their well-defined borders, recent parallels have been drawn to the remaining patches of wildlife habitats on large continents that appear nearly as ecologically insulated as islands.