Influence of endemic versus cosmopolitan species on the local assembly of ectomycorrhizal fungal communities.

An enduring question of community ecology is how remarkably speciose communities can coexist, particularly in light of competitive exclusion (Hutchinson, 1961). Ectomycorrhizal fungal (EMF) communities are no exception to this paradox; in a survey of old-growth Pseudotsuga menziesii stands, Kranabetter et al. (2018) reported a metacommunity (γ diversity or regional species pool) of approximately 360 EMF species on mesotrophic sites across a single watershed. Efforts to experimentally test EMF species interactions and community assembly can be insightful, but also hampered by the sheer number of taxa and difficulties in culturing an obligatory symbiosis under laboratory conditions (Kennedy, 2010; Branco, 2019). Similarly, the quantification of key morphological traits related to species distribution patterns, such as spore size and shape, can be instructive but inconclusive (Halbwachs et al., 2015; Kilvin, 2020). Given the challenges involved in an inductive approach, it may be advisable to employ perspectives from broader theoretical models to better understand the assembly of this ecologically important group. In this essay we describe how distinctions in geographical range for EMF species (regional to continental) can be used to better understand spatial processes governing local community assembly.