Ongoing plant invasion: increasing dispersal ability during range expansion

Invasive populations within the invaded range are often regarded as a homogeneous group in the studies of invasive plants. However, since invasive plants can evolve very rapidly and there may be lots of differences between old and young invasive populations, the homogeneous group may fail to tell us the complete evolutionary story behind the invasive populations, which motivated us to conduct studies on the evolution of invasive populations during range expansion within the invaded range.

In our study, now publihed Early View in Oikos, "Rapid evolution of dispersal-related traits during range expansion of an invasive vine Mikania micrantha", we were mostly concerned with the dispersal ability of the invasive populations. Although the results of the previous studies suggested that dispersal ability increases during range expansion, little is known on whether dispersal trends are genetically based or solely phenotypic in invasive plants. Using Mikania micrantha H.B.K. (Asteraceae), a highly invasive vine in southern China, we explored the spatial pattern of dispersal traits during range expansion. We asked whether the pattern, if any, was genetically based and whether it was driven by within-population pressures. The results showed that the dispersal ability of M. micrantha was selected for during range expansion. Interestingly, while dispersal traits in natural conditions decreased with increased distance from the source population, the same traits exhibited a significant humped trend against percent field cover in controlled conditions. These results suggested that the dispersal-related traits were under genetic control and that this evolutionary process was partially driven by intraspecific competition.

  This study suggested that plant species under spatial nonequilibirum can exhibit substantial trait differences along the invasion routes. We would have probably missed something in the evolution of invasive populations if they had been treated as a homogeneous group. Furthermore, our study can also provide hints about the fate of spatially fluctuant populations in the context of climate change.

Mikania micrantha in the field. M. micrantha usually forms dense canopies over the native plants, thus reducing light availability.

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