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Ecological theory suggests that a host organism's internal spatial structure can promote the persistence of mutualistic microbes by allowing for the turnover of tissue occupied by non-beneficial or cheating microbes. This type of regulation, whereby a host preferentially rewards tissue occupied by beneficial members of its microbiome but sanctions tissue occupied by non-beneficial cheaters, is expected to generate a competition–extinction trade-off by allowing beneficial microbes to experience a lower extinction rate than competitively dominant cheaters. Using an adaptive dynamics approach, we demonstrate that although ecologically stable, microbial regulation via sanctioning is not stable in any evolutionary sense, as each individual host will be under pressure to reduce the costs incurred from cheater suppression in order to maximize its own fitness at the expense of the rest of the host population. However, increasing the diversity of non-beneficial cheaters in the host population metamicrobiome can lead to an increase in the relative fitness of hosts that actively sanction non-performing tissue, thus facilitating the evolutionary emergence and persistence of such strategies in host-microbial systems. These counter-intuitive results demonstrate how diversity at multiple levels of biological organization and spatiotemporal scales can interact to facilitate the establishment and maintenance of mutualistic relationships. [ABSTRACT FROM AUTHOR]

1. Dispersal ability can influence the importance of dispersal relative to other processes organizing metacommunities, such as species sorting among habitats along environmental gradients. 2. We compare plants with different dispersal modes and habitat affinities, evaluating the roles of environmental and spatial controls on plant community composition in 128 wetlands within 10 km2 of old-growth maple-beech forest in southern Québec, Canada. 3. We address two hypotheses. First, we ask whether species with short-distance dispersal mechanisms are more dispersal-limited than species with adaptations for long-distance dispersal. Second, because wetland habitats are more fragmented than upland habitats in this forested area, we test the hypothesis that wetland species are more dispersal-limited than upland species growing in the same wetlands (e.g. on hummocks within a swamp). 4. Variation partitioning based on constrained ordinations showed that the distributions of species with short-distance dispersal mechanisms related more strongly to spatial factors than the distributions of long-distance dispersers, supporting the interpretation that these species are more dispersal-limited. The distributions of short-distance dispersers also showed finer-scale spatial patterns than the distributions of long-distance dispersers. 5. Distributions of wetland species related more strongly to environmental conditions than the distributions of upland species growing in the same wetlands, suggesting that wetland species are actually less dispersal-limited than upland species. Wetland and upland species had similar patterns of spatial variation in community composition. 6. Synthesis. The processes of dispersal limitation and species sorting along environmental gradients have differential importance to plants that grow within the same communities, but differ in dispersal ability and habitat affinity. This result emphasizes the impact of dispersal ability on the organization of metacommunities. [ABSTRACT FROM AUTHOR]