The distribution and abundance of lotic macroinvertebrates during Spring 1997 in seven streams of the western Santa Clara Valley area, California
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Open-File Report↗
Geology topics
Steven V. Fend
Publications and source records attributed to Steven V. Fend.
The interannual distribution and abundance of lotic invertebrates from five habitats of the Merced River in Yosemite Valley, Yosemite National Park, 1992-1995
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Open-File Report↗
The relationship of habitat characteristics to the distribution of chironomidae (Diptera) as measured by pupal exuviae collections in a large river system
Floating chironomid pupal exuviae were collected throughout the Yakima River (Washington, USA) and tributaries in 1989 and 1990. All samples were taken during the October-November low-flow season and most sites were visited once with a sampling effort of approximately 10 minutes. Sampled stream segments ranged from 3rd to 7th order and elevation ranged from 140–1200 m. The total number of taxa distinguished in 77 samples was 150 with a mean of 24 per site. Species richness was not highly correlated with stream order or elevation. An ecological gradient defined by ordinating the taxa by site data was highly correlated with site elevation (r=.93). Comparison with published attributes of chironomid genera suggested that temperature regime was a dominant environmental variable controlling chironomid distribution in this basin. However, since most measured habitat variables were associated with altitude, their effects could not be separated. Cluster analysis of taxa by site data resulted in groupings that distinguished montane from valley sites and agricultural drains from other valley sites. Differences in species composition between moderately enriched agricultural drains and less-impacted sites were minor compared with the underlying elevation gradient.
Washington↗
Use of detrended correspondence analysis to evaluate factors controlling spatial distribution of benthic insects
Detrended correspondence analysis (DCA) was evaluated for its effectiveness in displaying factors controlling the spatial distribution of benthic insects in an oligotrophic stream where an experimental gradient (copper) that selectively affects population abundances was imposed. DCA proved to be highly sensitive to differences among samples and consistently provided ecologically meaningful species ordinations. Seasonality of taxa was the major gradient displayed by DCA prior to copper exposure when data for all sampling dates were included. Sensitivity of taxa to copper was a more important factor affecting community structure than was seasonality during periods of continuous exposure to copper (2.5 to 15 µg l -1 Cu T ; approximately 12 to 75 ng l -1 Cu 2+ . When pre-dose data for each sampling date were ordinated independently, substratum composition and biological interactions were the major gradients displayed in species ordinations. During periods of exposure, sensitivity of taxa to copper was the primary gradient. This gradient also reflected a generally greater sensitivity to copper of herbivorous than of detritivorous or predatory benthic insects. DCA revealed the persistence, eleven months after dosing ceased, of differences in community structure between the control and high treatment (5 and 10 µg l -1 Cu T ) sections. Differences between sections were not evident on this sampling date from total biomass or total density (numerical) estimates.
Hydrobiologia↗