1. The ecological dynamics of co-flowering communities are largely mediated by pollinators. However, current understanding of pollinator-mediated interactions primarily relies on how co-flowering plants influence attraction of shared pollinators, and much less is known about plan-plant interactions that occur via heterospecific pollen (HP) transfer. Invaded communities in particular can be highly affected by the transfer of alien pollen, but the strength, drivers, and fitness consequences of these interactions at a community scale are not well understood.
2. Here we analyze HP transfer networks in nine coastal communities in the Yucatan Mexico that vary in the relative abundance of invasive flowers to evaluate how HP donation and receipt varies between native and alien plants. We further evaluate whether HP donation and receipt are mediated by floral traits (e.g. display, flower size) or pollinator visitation rate. Finally, we evaluated whether post-pollination success (proportion of pollen tubes produced) was affected by alien HP receipt and whether the effect varied between native and alien recipients.
3. HP transfer networks exhibit relatively high connectance (ca. 15%), suggesting high HP transfer within the studied communities. Significant network nestedness further suggests the existence of species that predominantly act as HP donors or recipients in the community. Species-level analyses showed that natives receive 80% more HP compared to alien species, and that alien plants donate 40% more HP than natives. HP receipt and donation were mediated by different floral traits and such effects were independent of plant origin (native or alien). The proportion of alien HP received significantly affected conspecific pollen tube success in natives, but not that of alien species.
4. Synthesis. Our results suggest that HP transfer in invaded communities is widespread, and that native and alien species play different roles within HP transfer networks, which are mediated by a different suite of floral traits. Alien species, in particular, play a central role as HP donors and are more tolerant to HP receipt than natives—a finding that points to two overlooked mechanisms facilitating alien plant invasion and success within native co-flowering communities.

In nine coastal communities, 3-4 styles per plant for all plants present within 10 plots were collected  (average per species 48.5 ± 68.95, ± SD). A total of 4500 styles were collected (average per site 498.22 ± 348.32, ± SD) corresponding to 1273 individual plants. Styles were collected from senesced flowers in the afternoon (» 1500 hrs), after pollinator activity had ceased, and were stored in formalin-acetic alcohol (FAA). For each style collected, the number of conspecific pollen (CP) and heterospecific pollen (HP) grains on stigmas, and the number of pollen tubes at the base of the style were scored with a fluorescence microscope (Nikon e2010).

To identify CP and HP pollen grains from plot-collected styles/stigmas, a pollen library was first created from mature floral buds (3-5) collected from each species present in the community. Pollen grains were photographed with an optical microscope equipped with a digital camera that allowed for the morphological characterization of pollen grains (Motic BA310). This pollen library was then used as a reference to identify pollen loads on stigmas and to record CP and HP abundance on each stigma.