Atop a windswept sea cliff at Bodega Marine Laboratory, UC Davis ecologists are learning about population dynamics from a moth-eaten patch of lupine bushes. The hardy plants are the unfortunate hosts to an outbreak of western tussock moth caterpillars. About an acre of bushes has been stripped of leaves; some bushes feed a thousand caterpillars. Yet all around, virtually identical lupines flourish unmunched. Susan Harrison, an associate professor of environmental studies, has studied the caterpillar outbreak for six years. Early on, she established that while the caterpillars are eating the lupines, something else is eating the caterpillars -- tiny flies and wasps called parasitoids that devour the caterpillars' eggs, larvae and pupae. In her newest study, reported in the Nov. 28 issue of the journal Science, Harrison and Davis postdoctoral researcher John Maron determined that the parasitoids are also the key to controlling the spread of the caterpillars. They discovered that parasitoids emanating from the outbreak suppress the caterpillars within a 200-yard "death zone." "For over 20 years, theoretical models have predicted that predators interacting with their prey could create patchy populations in continuous habitats," Harrison says, "but this study is the first to show it in a natural population."