Habitat selection and association of stream insects: a multivariate analysis

SUMMARY. Habitat selection and interspecies associations of stream insects were evaluated from a set of quantitative benthos samples and habitat measurements (velocity, depth, substrate, quantities of fine and leafy detritus) from a mountain stream. Substrate was characterized by an in situ grid method which effectively describes the size and distribution of the larger surficial materials within each sample unit. A principal components ordination of samples as characterized by abundance data over all species accounted for 54% of the total variance in three dimensions but implied continuous rather than discrete faunal change with habitat. Gradients in the habitat could not be identified with real confidence. Canonical correlation analysis identified three significant habitat‐fauna interactions. The first corresponded to the gradient from eroding to depositing substrates and included detritus abundance, the second distinguished areas of fine from leafy detritus and the third appeared to include velocity‐stone size interactions. A graphical technique based on ordination of physical data and clustering of associated species adequately summarized the distribution of five Ephemerella mayflies. The multivariate and interactive nature of stream bottom environments is discussed for problems involving prediction and experimental design and control.