Nested-subset structure of larval odonate assemblages in the Enoree River basin, USA


Communities have a nested-subset structure if the species found in species-poor assemblages are also found in progressively more species-rich assemblages. This nested-subset structure can be caused by differential colonization rates among species, differential extinction rates among species, or nested niche space. In this study, the assemblages of larval odonates in the Enoree River of South Carolina (USA) and nine of its tributaries were found to have statistically significant nested-subset structure. In addition, the degree of nestedness in these ten streams correlated with several chemical and physical variables. Nestedness was correlated with pH, turbidity, and concentrations of silica, bicarbonate, and calcium; suggesting that differential extinction in response to environmental stress may play a role in structuring these assemblages. However, nestedness also correlated with a crude measure of habitat homogeneity. Drainages with a heterogeneous mix of substrate types (cobbles and sand) maintained different sets of species from site to site, and had the lowest nestedness scores. Drainages with exclusively sandy substrates were dominated by burrowing species at all sites, and showed the strongest nested-subset patterns. As such, nested-subset structure in these assemblages is related to both chemical and physical parameters.

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