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Predicting fungal community dynamics requires methods combining theory with experiments. Different elements of spatial competition influence interaction outcomes, and consequently community dynamics. Despite the literature on such elements, no theoretical study has tested the predictability of dynamics with models incorporating these elements. We aimed to develop a method for predicting dynamics, to be tested first under laboratory conditions. Six spatial competition elements were quantified for three basidiomycete species on agar. We found: constant extension; extension unaffected by other mycelia; faster replacement of younger mycelial regions; faster replacement of smaller mycelia; uniform distribution of mycelial competitive ability across the boundary with heterospecifics; and additive effects of competition. We developed a lattice model, and found that incorporation of all experimentally quantified elements was necessary for accurate prediction of dynamics. Our study provides a methodological basis for prediction of fungal dynamics, and hence of ecosystem processes in which filamentous fungi are key players.

Community dynamics are mediated by species interactions, and within communities spatial heterogeneity and intransitive relationships promote coexistence. However, few experimental studies have assessed effects of heterogeneity on the interactions of competing individuals. Wood decay basidiomycete fungi are ideal for studying community structure and dynamics because they are easy to manipulate in laboratory microcosms, and communities resolve themselves rapidly. Most studies have only used simplistic pair-wise interactions in a 2-D plane, but here we investigate a three-species community in an environmentally realistic novel 3-dimensional system. We show how spatial heterogeneity and patch size dynamics are important for coexistence, and how competitive interactions change over different spatial dimensions. Emergent properties arose with increased spatial heterogeneity: the weakest competitor co-occurred with the community when its territory was less fragmented, and interactions became intransitive.