Subramanian, S. K.; Bolnick, D. I.

Eco-evolutionary theory predicts that local adaptation should influence community assembly and performance, yet empirical tests of these predictions remain limited, particularly at microgeographic scales where gene flow is expected to constrain adaptation. Using yeast communities in apple orchards as a model system, we tested whether local adaptation of a dominant species affects community composition and performance through reciprocal transplant experiments across eight Connecticut orchards and three apple varieties. The dominant yeast Hanseniaspora uvarum varied dramatically in abundance (4.3-97.5%) and exhibited significant local adaptation and maladaptation patterns across orchard-variety combinations. Critically, H. uvarum local adaptation strongly predicted community composition: locally adapted populations achieved higher abundance while suppressing competitors. However, local adaptation had no effect on community-level performance in apple decomposition. Communities dominated by locally adapted H. uvarum performed equivalently to diverse assemblages, indicating functional redundancy among species. These results demonstrate that rapid evolutionary change can decouple community composition from performance, suggesting that functional redundancy can maintain community performance despite dramatic compositional shifts driven by local adaptation.