Latitudinal variation in nematode diversity and ecological roles along the Chinese coast

Aim: To test changes in the phylogenetic relatedness, niche breadth, and life-history strategies of nematodes along a latitudinal gradient. Location: Sixteen wetland locations along the Pacific coast of China, from 20 degrees N to 40 degrees N. Methods: Linear regression was used to relate nematode phylogenetic relatedness (average taxonomic distinctness (AvTD) and average phylogenetic diversity [AvPD]), life-history group (based on "c-p" colonizer-persister group classification), and dietary specificity (based on guild classification of feeding selectivity) to latitude. Results: Wetland nematode taxonomic diversity (richness and Shannon diversity indices) decreased with increasing latitude along the Chinese coast. Phylogenetic diversity indices (AvTD and AvPD) significantly increased with increasing latitude. This indicates that at lower latitudes, species within the nematode community were more closely related. With increasing latitude, the nematode relative richness and abundance decreased for selective deposit feeders but increased for nonselective deposit feeders. The proportion of general opportunists decreased with increasing latitude, but persisters showed the opposite trend. The annual temperature range and the pH of sediments were more important than vegetation type in structuring nematode communities. Main conclusion: Nematode niche breadth was narrower at lower latitudes with respect to dietary specificity. Higher latitudes with a more variable climate favor r over K life-history strategists. Nematode communities at lower latitudes contained more closely related species.