Diversity patterns exhibited by the Plecoptera of a Coloradomountain stream

Abstract

Plecoptera collected from 11 locations along the longitudinal profile (first to fifth orders) of a Rocky Mountain stream(St. Vrain Creek) revealed distinctive spatial patterns of species diversity. Overall diversity was low near the stream source (epirhithron), attained maximum values in middle reaches, then declined dramatically concomitant with the transition from rhithron to potamon conditions. Shannon-Weaver index values ([math]) were < 1.0 at high elevations and at the potamon station, whereas [math] exceeded 3.0 in middle reaches. Species richness based on summer data alone is depressed by nearly 50 % at some locations, but the summer spatial pattern of [math] values is in general concordance with that derived from the entire data set. Species diversity patterns of consecutive summers were relatively stable considering the substantial differencesin discharge. To accurately determine Plecoptera diversity patterns, it was necessary to combine data from bothfine (240 µm) and coarse mesh (720 µm samples). Although a myriad of interrelated factors determine the diversity of loticinsects at a given site, summer maximum temperature and annual temperature range appear to be major variablescontrolling the spatial diversity pattern of Plecoptera.