The question has become more important in recent years as scientists campaign to preserve the planet's biodiversity, focusing on areas with the largest concentration of species, or attempt to restore native habitats and native species in the face of dramatic increases in the number of non-native invaders. Paradoxically, while many studies have shown that more diverse communities are better at resisting invaders, surveys of diverse ecosystems show they contain the highest number of exotic, non-native species. In a series of experiments reported in Science, Jonathan Levine, a graduate student in integrative biology, shows clearly that both are true. Small communities with high diversity are better at resisting invading species, but at larger scales, invaders are more likely to get established in diverse ecosystems.
Places are diverse for a reason.
So, you can't rely on biodiversity alone to prevent invasion. You have to keep exotic species from getting a foothold in the first place. Levine and one of his faculty advisers, Carla D'Antonio, associate professor of integrative biology, wrote a review article for the ecological journal Oikos last year that questioned the theoretical foundation and scientific support for the claim that diversity reduces susceptibility to invasion. People want to believe that, if we have more diversity in the ecosystem, it will be more resistant to invasion. Restoration ecologists want to create invasion-resistant communities.