Ecological and evolutionary diversification within the genus Carex (Cyperaceae): consequences for community assembly in subarctic fens

The concept of limiting similarity predicts that closely related taxa are less likely to co-occur than expected by chance. The degree to which the phylogenetic relatedness in plant communities is in accord with limiting similarity has been little tested at the scale where the consequences of adaptive differentiation during speciation should be most evident: the scale of neighboring, congeneric plants within a community. To quantify species co-occurrence patterns in relation to environment, we sampled sedge species, their rooting level relative to the water table, and the water pH in 2,124 0.25 m² quadrats distributed across 29 subarctic fens in the central Labrador Peninsula. We estimated phylogenetic relationships using four DNA regions (ETS, ITS, matK, trnL-trnF) for all species of Carex (42), Eriophorum (6), and Trichophorum (2) in the region, of which 21, four, and two, respectively, occurred in the sampled fens. We demonstrate that closely related species of Carex are less likely t...