Wind is a primary driver of fungal dispersal across a mainland-island system

1. Dispersal is one of the main processes shaping ecological communities. Yet, for species-rich communities in natural systems, the role of dispersal in community assembly remains relatively less studied compared to the role of other processes. This is especially the case for fungal communities, for which predictable knowledge about where and how the dispersal propagules move across space is largely lacking. 2. We sampled fungal communities at their dispersal stage in a mainland-island system, using a regular grid of 18 x 18 km, including sites on the mainland, islands, and over the water. Fungal communities were screened by applying DNA barcoding to air samples collected by cyclone samplers at the ground level. 3. To assess the factors determining fungal dispersal, we modeled aerial fungal communities with a joint species distribution model, including spore traits, weather-related predictors, and spatial predictors. We then built scenario simulations to predict how fungal species richness and spore size varied along the mainland-island connectivity gradient depending on wind speed conditions. 4. We found that the probability of occurrence of most species (and consequently species richness) was lower in low-connectivity sites (water and island) compared to high-connectivity sites (mainland). There was a high phylogenetic signal in how the fungal species responded to connectivity, indicating that some taxonomic groups are more dispersal limited than others, although such responses were not structured by their trophic guilds. Furthermore, wind speed influenced how species with different spore sizes responded to connectivity: in low-connectivity sites species with large sexual spores were detected especially when wind was high, whereas in low-connectivity sites they were detected especially when wind was low. 5. Synthesis. We show that fungi can be dispersal limited even at small spatial scales, and that fungal dispersal depends on the interaction between spore size and wind speed. This study demonstrates that fungal dispersal might be more predictable than previously considered and contributes to the mechanistic understanding of fungal air dispersal.