Community Structure I
Presiding: C Frady, Oregon State University; H Galbraith, Oklahoma Biological Survey and University of Oklahoma
NB31A-01 08:30h
Macroinvertebrate Communities and Benthic Organic Matter in Sand Habitats of 15 Northern Michigan Streams
Relationships between benthic organic matter (BOM) and macroinvertebrates have been well studied in streams with coarse substrates, but such relationships have been little studied in sand habitats, despite the abundance of sand in many streams. These relationships were investigated in sand habitats of 15 streams in three watersheds of the Ottawa National Forest, Michigan. Sand habitats in the 15 streams varied widely in mean total BOM quantity (112 to 1814 g AFDM·m-2) and size composition [very fine BOM (VFBOM, 0.45-250 Îœm), 0-58%; fine BOM (FBOM, 250 Îœm-1 mm), 11-27%; coarse BOM (CBOM, >1 mm), 27-81%] but differences were still detected among watersheds (VFBOM, ANOVA, F2,11 = 8.69, p = 0.005; CBOM, F2,11 = 11.15, p = 0.002). Sand-dwelling invertebrates were dominated by gathering-collectors, primarily Chironomidae (relative abundance = 73.6±15.4%; mean±SE; n = 15). Invertebrate biomass and mean body size differed among watersheds (biomass, F2,12 = 3.89, p = 0.050; body size, F2,12 = 6.12, p = 0.015). However, at this broad spatial scale, BOM quantity and quality had little effect on invertebrate community metrics in sand habitats. BOM content of sand habitats likely represents one factor, among many components of this dynamic habitat, which shapes overall macroinvertebrate communities.
NB31A-02 08:45h
Are New Zealand Springs really different: a Spanish comparison?
Patterns of invertebrate diversity were compared between rheocrene springbrooks, and nearby runoff fed streams in four regions of New Zealand and one region of Spain, Cantabria. Periphyton biomass, organic matter and moss were more abundant in springbrooks than in runoff-fed streams in both the Northern and Southern Hemisphere. Invertebrate species richness and density were greater in the springbrooks in New Zealand in all 4 regions. In contrast springbrooks in Spain had considerably lower species richness, but greater invertebrate densities than the runoff-fed streams. Differences in invertebrate diversity patterns between Spain and New Zealand springbrooks may be related to the larger diversity of invertebrate predators in New Zealand springbrooks, or the lack of temperature mediated life history cues in the New Zealand invertebrate fauna.
NB31A-03 09:00h
Water Mites (Acari: Hydrachnida) of Ozark Streams - Abundance, Species Richness, and Potential as Environmental Indicators
Because water mites are tightly linked to other stream metazoans through parasitism and predation, they are potentially effective indicators of environmental quality. Meiofauna (80 Îœm to 1 mm) were sampled from headwater riffles of 11 Ozark streams to determine relative abundance and densities of major meiofauna taxa. Water mites comprised 15.3% of the organisms collected exceeded only by chironomids (50.2%) and oligochaetes (17.8%), and mean water mite density among the 11 streams was 265 organisms per liter. The two streams that differed the most in environmental quality were sampled using techniques suitable for identification of species. An estimated 32 species from 20 genera and 13 families were found in the least disturbed stream; an estimated 19 species from 13 genera and 8 families were found in the most disturbed stream. This preliminary finding supports the notion that water mite species richness declines in response to environmental disturbance. Many species could only be identified as morphospecies of particular genera, but the ongoing taxonomic revision of Hydrachnida is expected to provide needed information. A collaborative effort between those interested in taxonomy/systematics of water mites and ecologists interested in the significance of water mites in aquatic communities could prove mutually beneficial.
NB31A-04 09:15h
Local and Regional Environmental Variables Important in Structuring Caddisfly (Trichoptera) Communities
Complex biotic and abiotic interactions coupled with the significance of scale have confounded the interpretation of community data. The use of multivariate statistical techniques has improved the way in which we are able to analyze this type of ecological data. We evaluated stream and riparian habitat features in southeastern Oklahoma at a range of spatial scales from local, in-stream variables to large-scale, regional characteristics to address the following questions: (1) How much variation in trichopteran community composition can be attributed to local, regional, and spatial variables? and (2) What environmental variables are most important in determining trichopteran community structure? Ten local and regional variables were identified as important to community structure using canonical correspondence analysis (CCA). In addition, straight-line distance between sampling sites and interconnectedness of the rivers are important in regulating caddisfly assemblages. We explained 71% of the variation in community composition with local habitat characteristics explaining the most variation (27.0%) followed by regional (8.9%) and spatial variables (2.5%). There was, however, considerable overlap in variation explained by these three suites of variables. Conservation efforts should minimize changes to river depth, substrate, and riparian conditions to preserve caddisfly communities.
NB31A-05 09:30h
Effects of Periphyton Quantity and Quality on the Benthic Community Characteristics of Five South Shore Lake Superior Tributaries
Pictured Rocks National Lakeshore (PRNL) is the largest protected wilderness area on the south shore of Lake Superior. The National Park Service is interested in assessing the condition of aquatic resources in PRNL, especially the Lake Superior tributaries which support populations of migratory brook trout ("coasters"). We conducted a multi-trophic level production study as part of a habitat assessment of PRNL streams to identify relationships between periphyton production and macroinvertebrate abundance and richness. Benthic invertebrates were collected using multi-plate style samplers. Periphyton respiration rate (CO2 efflux) and C:N ratio were measured to determine the quantity and quality of periphyton respectively. Invertebrate abundance and richness, and periphyton CO2 efflux differed significantly among streams and seasonally within each stream. Efflux was weakly correlated with stream discharge and water temperature. Invertebrate abundance increased with periphyton quantity, while richness tended to decrease with both periphyton quantity and quality. These results indicate that benthic invertebrate abundance and community composition are linked to variation in periphyton production, and that secondary production of benthic invertebrates may be effectively predicted by measuring periphyton efflux. This technique has applications as an alternative to traditional methods used by researchers in estimating secondary production of benthic invertebrates.
NB31A-06 09:45h
Comparisons of Aquatic Invertebrate Assemblages in Small, Old Growth and Second Growth Forested Catchments of the H.J. Andrews Experimental Forest, Oregon
In small streams, riparian vegetation often composes the food base for many aquatic invertebrates. Forest harvest can result in major changes to riparian vegetation. If abundance, richness, or community structure of invertebrate assemblages is affected by removal of riparian vegetation, are legacies of these practices evident 20-40 years post-harvest? If so, are these differences uniform through time, or are they temporally dependant? We investigated stream invertebrate assemblage dynamics between old growth and second growth forest types and across seasons in six small-basins in the H.J. Andrews Experimental Forest. Individual basins range from 500m to 1000m in elevation and 12.4ha to 98.1ha in area. Six benthic samples and four, 1-week emergence samples were collected in each basin each season (June 2003 through May 2004). Preliminary results from benthic samples suggest strong changes in community structure between seasons as additional taxa not found in summer (i.e. Agathon, Anagapetus, Chernokrilus, and Rhyacophila "angelita group") were collected in autumn and winter samples. However, results from summer comparisons demonstrate no differences in benthic and emergence abundance (p = 0.47, and p = 0.98, respectively) or benthic richness (p = 0.41) between old growth and second growth invertebrate assemblages.