Biodiversity has long been touted as important for staving off extinction. The more kinds of critters you have, in other words, the less likely any one of them—or a whole bunch of them—will disappear forever. The trouble is, no one has ever really demonstrated this idea in a lab setting. Until now. In a study published this month in Proceedings of the National Academy of Sciences, Dirk Sanders of the University of Exeter in the United Kingdom and his coauthors show that when you remove a species from a simple community—that is, a community with fewer overall species—it can trigger extinctions in other species.