The Nature and Consequences of Indirect Effects in Ecological Communities

mutualism. interaction. Abstract Indirect effects occur when the impact of one species on another requires the presence of a third species. They can arise in two general ways: through linked chains of direct interactions, and when a species changes the interactions among species. Indirect eff ects have been uncovered largely by experimen tal studies that have monitored the response of many species and discovered unexpected results, although some studies have looked for specific indirect effects predicted from simple models. The char acteristics of such approaches make it likely that the many indirect effects remain uncovered, but the appli­