There is a significant positive association between exotic plant species richness of an area and the human population size of that area. This association is notable not only for its high correlation (r2 = 0.69) but also because it spans five orders of magnitude for human population size. The correlation is apparently caused by the introduction of increasing numbers of exotic species as human population size grows. As population grows, so does exotic propagule importation and habitat disturbance. The regression is clearly asymptotic, indicating that per capita rates of exotic species introductions decline as human population continues to increase. A main implication for exotic species control is that efforts to limit exotic species will be most effective and least costly in areas (at many scales) where human population size is still relatively small. Another implication is that because human population size will continue to increase in many areas, educating the general public about harmful exotic species may be the only way to reduce rates of introduction, i.e., the slope of the regression.
Additional index words: Introduced species, exotic, weeds, human.
