Invasion status and phylogenetic relatedness predict cost of heterospecific pollen receipt: implications for native biodiversity decline

Abstract

Understanding the mechanisms by which invasive species affect native plants is a central challenge. Invasive plants have been shown to reduce pollinator visitation to natives and increase pollen quantity limitation. However, visitation and conspecific pollen delivery are the only two components of the pollination process; post-pollination interactions on the stigma (heterospecific pollen [HP] receipt) could intensify pre-pollination responses to invasion. Here, we used meta-analysis to test the hypotheses that invasive plants are more detrimental as HP donors than natives ones and that HP donors that are closely related to the recipients have stronger effects on fruit and seed production compared to distantly related ones. Invasive HP donors reduced fruit and seed production of recipients to a greater degree than native ones, and this was more intense for HP donors closely related to natives. Related donors were more detrimental overall. Synthesis. These results suggest that the total effect of invasive plants on native plant reproductive success could be greater than what is inferred from visitation and conspecific pollen transfer alone. Furthermore, these results indicate that invasive species can reduce reproductive success of native species even if pollinator visitation rates remain unaltered. Thus, we highlight the need to evaluate pre- and post-pollination processes in order to fully understand the potential effects of invasive species on the reproductive success and maintenance of native plant populations.