Successful plant invaders adapt to the pollination spectra of native flora but differ in diversity of pollinators

Background/Question/Methods

Mode of pollination is an important reproductive characteristic, assumed to play a role in species invasiveness. We asked whether (i) alien and native species differ in frequency of pollination modes, and (ii) whether the modes of pollination affects the invasion success of two groups of aliens, differing in their residence time in Central Europe: archaeophytes (introduced during several millenia since the beginning of Neolithic agriculture to the end of Medieval) and neophytes (introduced after 1500 A.D.). The analysis was carried using 2817 species occurring in the Czech Republic (1596 native, and 1221 aliens consisting of 331 archaeophytes and 890 neophytes). Data were analysed using general linear models, and classification and regression trees.

Results/Conclusions

Following introduction to a new region, alien species occurring as casuals harbour a high diversity of pollinators (higher than native species) and rely mainly on pollination by insects. However, the pollination spectrum found in casual neophytes gradually changes during the process of naturalization, becoming more similar to that of native species, and eventually, at the stage of invasion it reaches the structure typical of native species; at this stage there is no difference in frequency of the modes of pollination between invasive neophytes and native species. This implies that during invasion, alien species adapt to pollinator assemblages that are typical for the invaded region, and reflected by pollinator spectra of native flora. The role of self-pollination increases from casual to naturalized to invasion stage and proves to be, in terms of pollination mode, the best strategy for a successful invasion; self-pollination in neophytes leads to wider distribution in terms of the number of grid cells occupied than any other mode of pollination. The diversity of insect pollinator species harboured by plants of different status is determined by the range of habitats they occupy; the number of grid cells only plays role in co-determining the number of pollinator functional groups. In native species and invasive archaeophytes, accumulation of pollinator species with increasing range of habitats occupied proceeds faster than in other groups of aliens that arrived more recently. This indicates that groups of plants that have been provided with enough time to sample habitats more effectively than recently arriving alien species co-evolved more associations with pollinator species occurring in those habitats.