Invasion of exotic plants in disturbed sites is one of the most common observations in invasion biology. Given that many common exotics are ruderal, i.e. plants adapted to disturbed conditions, it is not surprising that they thrive in those sites. According to Grime’s plant strategy theory, ruderals should overcome plants with alternative strategies such as stress tolerant and competitive species in disturbed sites. It is less clear, however, how exotic ruderal species also overcome native ruderals in disturbed sites. One explanation for exotic ruderals success is that these species are adapted to disturbances that are novel for native species. For example, exotic ruderals from habitats with a longer history of human disturbance may overcome ruderal native species because they have been selected to perform well under disturbed conditions. Here, we studied the response of exotic and native ruderal species to natural and human disturbance in central Argentina, a region with a diverse ruderal community. Specifically, we conducted plant surveys in sites disturbed by natural disturbances such as fire and in sites disturbed by human activities such as road side plowing and grazing by domestic animals, and evaluated whether the origin of the ruderal community differs between these types of disturbances.

Results/Conclusions

The number of exotic ruderal plants in sites disturbed by road side plowing was more than ten and three times greater than that in sites disturbed by fire and domestic grazing, respectively. In turn, there were no differences in exotic ruderal invasion between fire and grazing.  In sharp contrast, the number of native ruderal plants in sites disturbed by fire and grazing doubled that in sites disturbed by road side plowing, and again no differences were detected between fire and grazing. These results suggest that exotic ruderal species perform better than native ruderals only under highly disturbed conditions, partially supporting the idea that exotics are adapted to disturbances that are novel to the recipient plant community.  The nature of this purportedly differential adaptation is, however, unknown and further research is needed to understand the pattern of ruderal distribution documented in this study.