Do endemic mushrooms on oceanic islands and archipelagos support the theory of island biogeography?

Abstract

Aim Terrestrial plant species on islands have a long history of study to determine how they evolved and what explains their levels of endemicity, but studies on fungi are lacking. Here, we examine: (1) how percent endemism of non‐lichenized class Agaricomycetes; hereafter, ‘mushrooms’ compares to angiosperms, ferns, bryophytes and lichens from oceanic islands/archipelagos; (2) whether endemic mushrooms evolved from an ancestor diversifying into multiple species after island colonization (cladogenesis) or over time evolved into a single endemic species unique from its ancestral mainland counterpart (anagenesis); and (3) if mushroom percent endemism and cladogenesis are correlated to geographic variables that help explain these phenomena in other species groups. Location Hawaiʻi, Galápagos, Canary Islands, Madeira, Azores, Cabo Verde, Christmas Island. Taxon Mushrooms, angiosperms, ferns, bryophytes, lichens. Methods Checklists of mushrooms and other species groups from seven oceanic islands/archipelagos were compared. Having multiple endemic congeners from a single island/archipelago was used to infer cladogenesis versus anagenesis in endemic mushrooms. Pearson's correlation coefficients were calculated between an island/archipelago's percent endemism and percent cladogenesis, and their distance to the nearest mainland, area, maximum elevation and latitude from the equator. Results Hawaiʻi has the highest mushroom endemicity at 83%, of which 50% are potentially derived from cladogenesis. Considering mushrooms on all islands/archipelagos, speciation by cladogenesis leads to fewer endemic species (37%) than anagenesis (63%). We find positive and statistically significant relationships between distance to mainland and island area with percent endemism among mushrooms, and cladogenesis is positively and significantly correlated with island size and maximum elevation. Main conclusions Mushrooms show greater percent endemism on larger, more isolated islands/archipelagos. However, they display the lowest percent species derived from cladogenesis among the organismal groups examined. Both the lack of data and unreliability of data are impediments to studying fungal endemism on islands, making drawing decisive conclusions challenging.

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