The phrase "invasive plant species" typically evokes negative images such as broad swaths of kudzu smothered trees along the highway or purple loosestrife taking over wetlands and clogging waterwaysand as such, invasive plants are largely viewed as major threats to native biodiversity. However, research has shown both that invasive species may be one of the most important threats to biodiversity and that plant invasions are rarely the cause for native species extinctions. How can these conflicting pieces of evidence be reconciled?
Kristin Powell, from Washington University, MO, was interested in determining whether some of the differences in the effects that invasive plant species had on biodiversity was in fact due to the spatial scales at which they were studied.
"Biological invasions are often thought to be one of the leading threats to global biodiversity," Powell comments. "However, recent studies and popular literature have begun to question this view, especially in the context of invasive plants, asking 'Are invasive species really that bad?' For example, invasive plants have never been implicated as the sole cause in driving a native plant extinct."
To tackle this apparent conundrum, Powell and her co-authors took a two-prong approach; first, they conducted a meta-analysis to synthesize results from as many previous studies on the subject as they could find, and then they developed a model to investigate mechanisms that might explain their results. They published their findings in the recent Biodiversity Special Issue of the American Journal of Botany (http://www.amjbot.org/cgi/reprint/98/3/539).
Powell and her colleagues found 57 studies containing information on average species richness with and without invaders. They used a meta-analysis because it is a powerful tool that allows each study to be used as a separate data set, to some degree. B
|Contact: Richard Hund|
American Journal of Botany