Abstract
Plant colonization of islands may be limited by the availability of symbionts, particularly arbuscular mycorrhizal (AM) fungi, which have limited dispersal ability compared to ectomycorrhizal and ericoid (EEM) as well as orchid mycorrhizal (ORC) fungi. We tested for such differential island colonization within contemporary angiosperm floras worldwide. We found evidence that AM plants experience a stronger mycorrhizal filter than other mycorrhizal or non-mycorrhizal (NM) plant species, with decreased proportions of native AM plant species on islands relative to mainlands. This effect intensified with island isolation, particularly for non-endemic plant species. The proportion of endemic AM plant species increased with island isolation, consistent with diversification filling niches left open by the mycorrhizal filter. We further found evidence of humans overcoming the initial mycorrhizal filter. Naturalized floras showed higher proportions of AM plant species than native floras, a pattern that increased with increasing isolation and land-use intensity. This work provides evidence that mycorrhizal fungal symbionts shape plant colonization of islands and subsequent diversification.
Highlights
Plant colonization of islands may be limited by the availability of symbionts, arbuscular mycorrhizal (AM) fungi, which have limited dispersal ability compared to ectomycorrhizal and ericoid (EEM) as well as orchid mycorrhizal (ORC) fungi
We test for differences in the strength of the mycorrhizal filter across plant species associating with the three major mycorrhizal types: arbuscular mycorrhizal (AM) fungi, the most common type of mycorrhizae, ectomycorrhizal and ericoid mycorrhizal (EEM)
We found support for dispersal limitation of native angiosperm plant species that associate with AM fungi (Figs. 1a and 2a, c, supplementary tables 1–6)
Summary
Plant colonization of islands may be limited by the availability of symbionts, arbuscular mycorrhizal (AM) fungi, which have limited dispersal ability compared to ectomycorrhizal and ericoid (EEM) as well as orchid mycorrhizal (ORC) fungi. We tested for such differential island colonization within contemporary angiosperm floras worldwide. Individual fungal species of other types of mycorrhizae, EEM, have adaptations for aerial dispersal of spores[13,14] and can grow independently of their host through saprophytic activity[12,15,16,17,18,19,20] (but see Lindahl et al.[21]). We expect EEM and ORC fungi to be better able to establish on islands prior to their hosts compared to AM fungi, and EEM and orchid plant species to be less impacted by the mycorrhizal filter than AM plant species[22]
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