Effects of Canopy, Substrate Composition, and Gradient on the Structure of Macroinvertebrate Communities in Cascade Range Streams of Oregon

Abstract

The relative importance of surrounding riparian vegetation and substrate composition on invertebrate community structure was investigated in six streams in Oregon, USA. We found that canopy type was more important than substrate character in influencing total abundance and guild structure. Streams without shading had higher abundances of invertebrates than did shaded steams. Most guilds were influenced by qualitative differences in food availability rather than quantity of food or substrate composition. Open streams had higher abundances in the collector—gatherer, filter feeder, herbivore shredder and piercer, and predator guilds. Contrary to expectations, shredders were no more abundant in shaded streams than in streams lacking a riparian canopy. Scraper density was inversely related to standing crop of aufwuchs, but biomass was positively correlated with quantity of aufwuchs. Examination of dominance—diversity curves showed that both canopy and substrate influenced ranked abundances of taxa, but neither canopy nor substrate strongly influenced number of taxa. Differences in community structure were not always revealed by analysis of community—level properties, although differences in both the absolute and relative abundances of individual taxa were observed.

Secondary production of chironomid communities in insecticide‐treated and untreated headwater streams

“…VFBOM) in C53 compared with C55, in terms of higher standing crops and lower ash content, may have contributed to higher levels of chironomid production. Several studies have reported positive relationships between densities of various stream invertebrates and apparent food availability (Hawkins, 1986;Hawkins, Murphy & Anderson, 1982;Cummins et al, 1980;Drake, 1982). However, in the present study, only the densities of chironomids collected on the rock outcrops and those from the benthic cores in C53 showed a positive relationship with standing crops of VFBOM.…”

Effects of riparian willow trees(Salix fragilis)on macroinvertebrate densities in two small Central Otago, New Zealand, streams

“…This effect was observed across nearly all functional feeding groups in pools and riffles of both streams in all seasons. Similar effects of riparian trees on stream invertebrate abundance have been reported elsewhere in New Zealand (Allen 1951;Hopkins 1976;Graynoth 1979;Suren 1992), and overseas (Hughes 1966;Hawkins et al 1982;Behmer & Hawkins 1986). Two major hypotheses have been proposed to account for such results that they are a food chain effect reflecting lower primary production due to shading by trees, and/or an effect of substrate size.…”

“…Detrital food quality has long been associated with densities or growth rates of stream invertebrates (Anderson & Cummins 1979;Hawkins et al 1982). Although we found similar levels of SSOL and FPOM at all sites, if riparian vegetation reduced the production of high quality detritus derived from algae, and replaced it with detritus of lower quality from willow leaves, then this may have contributed to the lower invertebrate densities at willow sites.…”

Macroinvertebrate communities along a third-order Iberian stream

“…For example, some authors have noted that open reaches, as it is the case for site 7, support higher invertebrate abundance than canopied ones (e.g. Hopkins 1976, Hawkins et al 1982, Behmer & Hawkins 1986, Maridet et al 1998, which is attributed to higher food quality of periphyton than leaf detritus (Anderson & Cummins 1979). On the other hand, high faunal density at site 9 could be a consequence of the organic sewage from Guriezo which allows high densities of Chironomidae and Oligochaeta (Wiederholm 1984).…”

“…Spatial changes in CPOM quality could obscure the relationship between shredders and their food (e.g. Smock & MacGregor 1988, Hawkins et al 1982, Dudgeon & Wu 1999. At the present study, higher shredder biomass -CPOM stocks ratios were found at downstream reaches than at headwater (9.0, 8.4 and 7.3 in sites 9, 7 and B) suggesting that 1) shredders would be less limited by CPOM quantity at site B, a forested, headwater reach, than at the downstream sites, and 2) shredders were more efficient in CPOM use in downstream reaches, a fact reported previously by Basaguren et al (1996).…”