Macroecological Patterns of Estuarine Nematodes

In the present study, we test whether large-scale patterns of estuarine nematodes are predicted by the “everything is everywhere” (EiE) hypothesis or by the moderate endemicity hypothesis (MEH). Specifically, we tested whether nematode genus richness and composition differ among geographical regions, latitudes, and between habitats (estuaries with and without mangroves). The meta-analysis included published data from 43 estuaries around the world. Only the most abundant genera (>1 % of relative abundance) were considered in the analysis. Each estuary was treated as an analytical unit. Results indicated that genus richness did not differ among geographical regions and between habitats, whereas latitude explained 36 % of the variability in genus richness. Genus richness assumed a bimodal pattern with higher values around the equator and in temperate regions. Canonical analysis revealed distinct nematode genus compositions in three main geographical regions and in both habitat types. These results suggest that nematodes are dispersion-limited and influenced by environmental conditions. The main conclusion is that large-scale patterns of estuarine nematodes are better predicted by the MEH, in line with studies of macroorganisms. Moreover, nematode genus turnover decreased with increasing latitude, a pattern already reported for harpacticoid copepods, land birds, vascular plants, mammals, and butterflies.