The dimensionality of biodiversity of stream insects in the conterminous US: 2!

The analyses of the dimensionality of biodiversity are key to improve our understanding of processes shaping local communities. Here, we used a dataset on stream insects to estimate the dimensionality of biodiversity at the scale of the conterminous United States. We also assessed which facets of biodiversity maximized stream differentiation, which complexes of biodiversity measures were formed, and how these biodiversity measures were correlated with an environmental gradient across stream sites. In general, we found that two sets of biodiversity measures maximized the differentiation among streams. The first set was composed by indices reflecting the taxonomic relationships among taxa and trait diversity measures, whereas the second set was composed by indices reflecting trait richness, genus richness, and Pielou’s evenness. We found that only the first set of indices was correlated with an environmental gradient across the USA and that the higher the importance of a biodiversity measure to differentiate streams, the higher its relationship with the environmental gradient. These results support the view that different facets provide complementary insights into spatial patterns of biodiversity of stream insects and that measures that consider the taxonomic relatedness among taxa and trait information are the most responsive to the identified environmental gradient.