However, establishment on islands could also be limited by biotic drivers, such as the absence of symbionts. Most plants, for example, form symbioses with mycorrhizal fungi, whose limited dispersal to islands could act as a colonization filter for plants. An international team of researchers, among them Franz Essl from the Department of Botany and Biodiversity tested this hypothesis using global-scale analyses of ~1.4 million plant occurrences, including ~200,000 plant species across ~1,100 regions. They found evidence for a mycorrhizal filter (that is, the filtering out of mycorrhizal plants on islands), with mycorrhizal associations less common among native island plants than native mainland plants. Furthermore, the proportion of native mycorrhizal plants in island floras decreased with isolation, possibly as a consequence of a decline in symbiont establishment.

Delavaux CS, Weigelt P, Dawson W, Duchicela J, Essl F, van Kleunen M, König C, Pergl J, Pyšek P, Stein S, Winter M, Schultz P, Kreft H & Bever JD (2019) 'Mycorrhizal fungi influence global plant biogeography. Nature Ecology and Evolution. DOI: http://dx.doi.org/10.1038/s41559-019-0823-4.