Spatial structure of Ephemeroptera, Plecoptera, and Trichoptera larval abundance in a northern Idaho stream: Multiscaled multivariate analyses of local variability

Hierarchy theory reveals different patterns of organism distribution and associations with their physical habitat to exist at different scales of spatial resolution. Multiscaling clarifies observed associations among data sets by helping to resolve putative statistical noise into hierarchical structure. A multiscaled multivariate procedure was used to reduce nuisance variability and data redundancy at the local scale, improving interpretation of local spatial variability. Samples of benthic insects and measures of their physical habitat were collected from 18 riffles within the ecosite of lower Lapwai Creek, Idaho, from 1997--1999. Sample scales were constructed by considering all samples as separate, then combining adjacent sample pairs, triplets of adjacent samples, and all six samples within each riffle.; High water prevented collection of physical habitat data during 1997. Flows decreased progressively in 1998 and 1999. The total abundance of Ephemeroptera, Plecoptera, and Trichoptera (EPT) declined 35.4% over the survey period. Trichopteran collector-filterer abundance declined by 47.6%, while Cheumatopsyche spp. increased by 64.1%. Baetidae declined by 51.8%, while non-baetid ephemeropteran collector-gatherers increased by 89.7%. Taxa richness changed little (48.3 +/- 4 taxa), sampling effort curves indicated 25% of the 108 samples each year accounted for observed taxa richness, and rank-abundance curves consistently represented a geometric series (alpha diversity = 4.59 +/- 0.37).; Principal components analyses were used to independently assess each data set for sufficient structure and pattern to permit further examination with canonical correlation analysis (CCA). Yet, insect vagility and habitat specificity commonly emerged as dominant sources of structural influence. CCA retained the first pair of canonical variables for both 1998 and 1999. Although canonical coefficients of determination indicated strong scale-dependent relationships, sufficient variability remained to yield low inference power. However, the natural log of the abundance of predators and Epeorus albertae were found to correlate predictively with current velocity and cobble size, and were scale dependent. The importance of either habitat variable to the relationship depended on annual flow, and the interaction with cobble size at lower flows. Hierarchical structure changed among years as the EPT assemblage responded to changing stream flow. Interpretations and ramifications of these findings are discussed.