Stable isotope values of lotic invertebrates: Sources of variation, experimental design, and statistical interpretation

Abstract

In a subset of a stream food web, whole-body isotope values of δ13C and δ15N were measured for eight populations of lotic invertebrates. Observed isotopic differences among species corresponded broadly to their trophic status, as also revealed by gut content analysis, but with some exceptions. Species within a guild of grazer/scraper mayflies differed significantly in δ13C; a predatory caddisfly (Rhyacophila dorsalis) and a collector/gatherer stonefly (Leuctra inermis) had statistically indistinguishable values of δ13C and δ15N. The variation associated with the mean isotope value of each population was partitioned into the variation among individuals and the variation that arises from analy..