While most introduced species never become established, some “have just gone crazy [and] changed, from being nice guys—good citizens coexisting with other species—into these competitive monsters,” according to University of Montana plant ecologist Ragan Callaway. One secret to invasive species' success is a knack for manipulating soil organisms in their adoptive habitat to their own advantage, according to a paper by Callaway and colleagues in the February 19 Nature (Nature, 427:731-733, February 19, 2004).

The “competitive monster” studied by Callaway and colleagues was spotted knapweed (Centaurea maculosa), a European native that has spread to all 50 US states since its introduction in the late 1800s. They took a biogeographic approach, comparing the feedback effects that arise between the plant and soil microbes when it is grown in soil taken from its native versus adoptive habitat.

The authors showed that soil microbes from the plant's home...

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