Species microdistribution of larval Chironomidae (Diptera) on riverbed cobbles at riffles: a quantification using artificial substrates

摘要

Distribution patterns of organisms are influenced by the scale investigated (GILLER & GEE 1987, HORNE & SCHNEIDER 1995). Studies on distribution of benthic macroinvertebrates in streams have been conducted at various scales, from the sur-face of an individual rock (RADER & WARD 1990) to stream reaches and entire basins (CORKUM 1992, Roy et al. 2003, INOUE et al. 2005). Many studies on microdistribution of lotic Chironomidae have focused on habitat heterogeneity in fine substrates (RAE 1985, 2004, RUSE 1994). BOUCKAERT & DAVIS (1998), however, showed that chironomid density was higher on upstream sides of boul-ders than downstream sides. RADER & WARD (1990) placed ar-tificial brick substrates in a stream and demonstrated that chi-ronomids attached to all surfaces, but the density was highest on "bottom" surfaces. Microdistribution patterns on the sur-faces of riverbed stones should be different among species and, especially stone bottoms and interstices, should be affected by presence/absence of leaf litter caught in interstices because lit-ter is a major food source for benthic macroinvertebrates. We compared species richness, total density, and commu-nity composition of chironomids among surface types by plac-ing standardized artificial substrates in riffles instead of natu-ral cobbles in streams with and without riparian canopy.