Successful invaders co-opt pollinators of native flora and accumulate insect pollinators with increasing residence time

Abstract

Pollination mode is an important reproductive characteristic, often assumed to play a considerable role in plant species invasiveness. We asked (1) whether alien and native species differed in the frequency of pollination modes (insect pollination, self-pollination, wind pollination, water pollination), (2) whether the pollination modes affected the invasion success of two groups of aliens, differing in their residence time in Central Europe: archaeophytes (introduced before 1500) and neophytes (introduced more recently), and (3) whether there were differences in the diversity of insect pollinators of native species, and of alien species at different stages of invasion and with different residence time. The analysis was carried out using 2817 species occurring in the Czech Republic (1596 native and 1221 alien, the latter comprising 331 archaeophytes and 890 neophytes). Data were analyzed using generalized linear models. The alien flora introduced to Central Europe contained a higher proportion of insect-pollinated species than did the Central European native flora and linked to a higher diversity of pollinators per species. However, the frequency of pollination modes in the introduced alien flora gradually changed during the process of naturalization, becoming more similar to that of native species, and eventually, the naturalized species that became invasive did not differ in their frequency of pollination modes from native species. The frequency of self-pollination increased from casual through naturalized to invasive alien species. This suggests a remarkable role for pollination mode in successful invasions; indeed, self-pollination tends to support spread of neophytes more than any other mode of pollination. The range of habitats occupied by plants of different invasion status affected the diversity of insect pollinator species. In contrast, regional commonness of plant species only affected the number of pollinator functional groups. In native species and archaeophytes, there was a steeper accumulation of pollinator species with increasing habitat range than in neophytes. This indicates that groups of plants that have been provided with longer time to sample a wider range of habitats than recently arriving alien species have formed more associations with native pollinator species occurring in those habitats.