Effects of habitat types and within lake environmental gradients on the diversity of chironomid assemblages

Understanding the distribution of biotic diversity across various spatial scales and environmental gradients is important from fundamental, practical and conservation biological aspects. We applied a hierarchical diversity partitioning framework to quantify the variability of sample level α- and β1-diversity, and environment related β2-diversity of benthic chironomid assemblages within and among a priori defined habitat types, and along the gradients of individual environmental factors in a large and shallow lake (Lake Balaton, Hungary). Taxon richness (both additive and multiplicative) and Shannon index based diversity approaches yielded highly concordant results. The α-diversity was much lower and β1-diversity higher than predicted by null model and both measures varied substantially among habitat types and along most individual environmental gradients. The β2-diversity indicated a marked variability of taxon (identified at species to genus level) pool among habitat types and higher than predicted taxon turnover along all examined environmental gradients. Moreover, the observed β2-diversity varied greatly among individual environmental gradients. The difference between the expected and observed β2-diversity values suggests that taxon turnover was most influential (in decreasing order) along the algae coverage gradient, the lake bed substratum gradient and the macrophyte coverage gradient among others. We argue that within-lake environmental heterogeneity and its effect on the taxon richness should receive more attention in biodiversity assessment and conservation. Management could benefit from the identification of within lake gradients along which taxonomic turnover maximizes.