Invasion ecology: Origin and biodiversity effects

The history of invasion ecology, with respect to its mid-19 th century beginning and its extended relationship with island biogeography, has not been investigated. In fact, most historical accounts begin with the publication of Charles Elton’s book in 1958. Since that time, the field has undergone a phenomenal growth until it has become a major specialty area related to ecology, biogeography, and macroecology. Over the years, invasion studies have made significant contributions to knowledge in the areas of colonization, adaptation, biodiversity, evolution, and species relationships. But also, many ecologists became convinced that invasive species were responsible for native extinctions and the loss of biodiversity. However, new studies, based upon documented extinctions and their causes, have shown that invaders are rarely implicated. Instead, successful (colonizing) invaders are almost invariably accommodated by the native species that occupy the necessary habitat. Accommodation results in a gain in species diversity of the invaded area. Diversity gain generally results in a more stable system with higher productivity and a greater resistance to invasion. Furthermore, as the fossil data indicate, invasions may eventually result in additional speciation that adds to global biodiversity. These data provide evidence of a dynamic, global system consisting of successful invasions that extend from high species diversity centers outward to where diversity is less and the competition weaker.