Abstract
Two alien species in Europe, Impatiens glandulifera and I. balfourii, are closely related, have similar growth rates and reproductive capacities, and are very attractive to pollinators. Nevertheless, only I. glandulifera is a highly invasive alien species in Europe, while I. balfourii is non-invasive. We assumed that the varying levels of invasiveness are driven by differences in the floating ability of their seeds, which may determine the invasion success of riparian alien plants, such as the Impatiens species. By mimicking two types of aquatic conditions, we determined seed floating ability for each species from younger and older populations. We also analyzed four seed traits: seed viability, surface, shape and coat structure. Seeds of the non-invasive I. balfourii float less well than seeds of the invasive I. glandulifera. We also found that the seeds of I. balfourii from the younger population have a higher floating ability in comparison with that of the seeds from the older population. The results for I. glandulifera were the opposite, with decreased floating ability in the younger population. These differences were associated with seed surface, shape and coat structure. These results indicate that the floating ability of I. balfourii seeds may increase over time following its introduction into a given area, while in the case of I. glandulifera, this ability may gradually decrease. Therefore, the former species, currently regarded as a poor disperser, has the potential to become invasive in the future, whereas the latter does not seem to benefit from further investments in the floating ability of its seeds.
Highlights
Identifying the factors that determine the invasive behaviors of species introduced to new areas is an increasingly important task both for theoretical aspects of ecology and for practical implications in nature conservation and economics (Vazquez and Morales 2011)
The differences between the species were greater when the seeds were derived from older populations than when they were derived from younger populations
We showed that the ability of seeds to float may promote the invasiveness of alien plant species
Summary
Identifying the factors that determine the invasive behaviors of species introduced to new areas is an increasingly important task both for theoretical aspects of ecology and for practical implications in nature conservation and economics (Vazquez and Morales 2011). Previous comparative studies of I. balfourii and I. glandulifera demonstrated that they are similar in terms of their photosynthetic capacities, growth rates (Ugoletti et al 2011), attractiveness to pollinators, self-compatibility, high reproductive capacity (Jacquemart et al 2015; Ugoletti et al 2011) and lack of inbreeding depression (Jacquemart et al 2015). It is thought that invasion by this species may still be in a lag phase, as it was introduced 60 years later than its invasive counterpart (Adamowski 2009). Neither of these two hypotheses has ever been verified
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