2021, Malecore, Eva M., Berthelot, Sylvie, van Kleunen, Mark, Razanajatovo, Mialy

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.

2019-03, Malecore, Eva M., Dawson, Wayne, Kempel, Anne, Müller, Gregor, van Kleunen, Mark

1.The phylogenetic distance of an introduced plant species to a resident native community may play a role in determining its establishment success. While Darwin's naturalization hypothesis predicts a positive relationship, the preadaptation hypothesis predicts a negative relationship. Rigorous tests of this now so‐called Darwin's naturalization conundrum require not only information on establishment successes but also of failures, which is frequently not available. Such essential information, however, can be provided by experimental introductions.

2.Here, we analysed three datasets from two field experiments in Germany and Switzerland. In the Swiss experiment, alien and native grassland species were introduced as seeds only with and without disturbance (tilling). In the German experiment, alien and native grassland species were introduced both as seeds and as seedlings with and without disturbance (tilling), and with and without fungicide application. For the seedling introduction experiment, there was an additional herbivore‐exclusion treatment.

3.Phylogenetic distance affected establishment in the three datasets differently, with success peaking at intermediate distances for the seed datasets, but decreasing with increasing distances in the seedling dataset. Disturbance favoured seedling survival, most likely by weakening the resident community.

4.Synthesis: By analysing experimental introductions, we show that the relationship between phylogenetic distance and establishment, at least for seedling emergence, may actually be non‐linear with an optimum at intermediate distances. Therefore, Darwin′s naturalization hypothesis and the preadaptation hypothesis need not be in conflict. Rather, the mechanisms underlying them can operate simultaneously or alternately depending on the life stage and on the environmental conditions of the resident community.