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Local adaptation can influence how species affect community composition, yet data quantifying the relative importance of local adaptation compared with species presence is lacking. To address this, we followed the dynamics of a natural bacterial soil (compost) community exposed to elevated temperatures over two months where adaptation and presence per se of a focal species was manipulated. Specifically, we inoculated the natural compost community with either: 1) the ancestral bacterium Pseudomonas fluorescens SBW25; or 2) SBW25 that had been locally adapted to these conditions for 48 days (apparent from a large fitness increase and correlated genomic changes); or 3) no SBW25. We detected large differences in community composition between treatments, with the effect of adaptation as great as the effect of the presence of SBW25 per se. Local adaptation, however, had a much smaller relative effect than species presence on community population dynamics, and neither treatments significantly affected community diversity metrics. These affects were robust to strong additional selection pressures imposed on the focal species, with the magnitude of effect of SBW25 on the community little affected when its densities were reduced by the presence of lytic virus. Our results show that contemporaneous adaptive evolution can play as great a role as species presence in structuring natural microbial communities. Our conclusions are likely to be particularly relevant to situations where a few species may have an evolutionary head start following colonisation of novel habitats or large perturbations, including the plant rhizosphere in agricultural systems and the gut microbiome exposed to antibiotics. |