Reciprocal heterospecific pollen interference among alien and native species.
Heterospecific pollen interference has recently been proposed as a mechanism contributing to the success of alien invaders, as heterospecific pollen of alien plants can interfere with the reproduction of natives by reducing fruit and seed set. However, no study has looked at the opposite interaction. Moreover, few studies have considered the roles of phylogenetic and floral trait distances between pollen donors and recipients. We did a large multi-species experiment in which we used alien and native species both as pollen recipients and as pollen donors, and included phylogenetic as well as single floral trait distance as explanatory variables. We found that both alien and native recipients suffered from heterospecific pollen from donors of the opposite status in terms of seed and fruit set. Phylogenetic distance did not affect fruit and seed set. However, style-length distance decreased, while pollen-size distance increased heterospecific pollen interference. We conclude that heterospecific pollen interference affects both native and alien recipients, thus indirectly altering community composition. Importantly, we found that heterospecific pollen interference can be a mechanism that increases biotic resistance of natives against invaders.