Alien species pool influences the level of habitat invasion in intercontinental exchange of alien plants
We hypothesize that the level of plant invasion at the scale of vegetation plots is affected by the different sizes of regional species pools of alien plants adapted to particular habitats. We test these species-pool effects in the context of alien species exchange between analogous habitats on two continents.
North and South Carolina, and the Czech Republic (both as native and invaded range).
We identified native and alien vascular plant species within 6059 vegetation plots from 27 habitats of eastern North America and Central Europe. We compared the habitats’ level of invasion, expressed as the proportion of alien species in a representative sample of vegetation plots from each habitat, with the contribution of each habitat to the alien species pool, calculated as the proportion of species of this habitat that are native to one continent and donated as aliens to the other.
A habitat's level of invasion on one continent increases with the proportion of alien species donated to its regional species pools by analogous habitats on the other continent, i.e. the more of its native species a habitat contributes as aliens, the more of them establish in analogous recipient habitats (direct species-pool effect). The habitat's level of invasion on the same continent also increases with the proportion of native species that those habitats themselves donate to regional species pools on the other continent, i.e. a habitat that gives many aliens also receives many aliens (reciprocal species-pool effect).
We demonstrate that when a habitat on one continent donates more of its native species to the alien species pool, the analogous habitat on the recipient continent also contains a greater number of aliens. The same donor habitat is itself also the recipient of more alien species invading from the analogous habitats of other continents.