Canadian Forest Service Publications
Ecological and evolutionary diversification within the genus Carex (Cyperaceae): consequences for community assembly in subarctic fens. 2016. Waterway, M.J.; Martins, K.T.; Dabros, A.; Prado, A.; Lechowicz, M.J. Systematic Botany 41(3):558-579.
Issued by: Northern Forestry Centre
Catalog ID: 37250
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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 to co-occur than expected by chance using 1) a probabilistic method to test the significance of pairwise co-occurrence patterns of species, and 2) linear mixed modeling to relate these patterns to phylogenetic relationships and ecological tolerances along gradients of substrate pH and rooting level in relation to the water table. The results also indicate that suites of species with significant mutual pairwise co-occurrence belong to distant lineages within the Cariceae-Dulichieae-Scirpeae clade of Cyperaceae and have stabilizing niche differences. We suggest that niche differentiation during the evolution and diversification of a clade of wetland Carex species over the past few million years, especially during the dynamic glacial cycles of the Pleistocene, has resulted in diverse sedge communities that share space and resources in harsh northern peatland habitats.
Plain Language Summary
In ecology, the concept of limiting similarity predicts that the more closely related species are, the less likely they are to occur together. Closely related species would ordinarily compete for many of the same resources, so they might have developed different life strategies to reduce the likelihood of direct competition. As a result, over millions of years their niches might have diverged. We tested whether this theory applies down to the scale of interactions between neighbouring individuals by comparing the co-occurrence of sedge species in more than 2000 small (0.25 m2) plots distributed across 29 subarctic fens in the central Labrador Peninsula. We used DNA analyses to estimate how closely the plants we sampled were related. We found that closely related sedge species are less likely to co-occur than expected by chance. For example, a pair of very closely related species might have a differing preference for a rooting depth, with one species occurring along the fen shores and the other rooting in deeper water away from the shore. Our results suggest that niche differentiation during the evolution and diversification of wetland sedge species over the past few million years has resulted in diverse sedge communities that efficiently share space and resources in harsh northern peatland habitats. The information obtained in this study about species distribution in natural habitats may be helpful in understanding why certain species may or may not be well suited to growing close to each other. This may be relevant when plans are being made to revegetate areas that have been disturbed by industrial activity.