Life on Earth is experiencing its sixth major extinction event. This event differs from previous ones because it is caused by human activity. There is increasing scientific and public concern over the massive loss in biodiversity (all aspects of biological diversity, including species richness, ecosystem complexity, and genetic variability). Convincing evidence since the 1960s shows that ecosystem functioning is dependent on attributes of individual species. Only recently have ecologists examined how species diversity affects ecosystem processes. The importance of ecosystem complexity and genetic variability remains largely unexplored.