Macroinvertebrate species list of the Andrews Experimental Forest, 1992
- PRINCIPAL INVESTIGATOR:
- Judith L. Li
- Stanley V. Gregory
- OTHER RESEARCHER:
- Alan Herlihy, William J. Gerth, Philip Kaufmann
- DATA SET CONTACT PERSON:
- Donald L. Henshaw
- Suzanne M. Remillard
- METADATA CREATION DATE:
- 20 Oct 1995
- MOST RECENT METADATA REVIEW DATE:
- 31 Dec 2013
- Insects, Long-Term Ecological Research (LTER), Populations, Spatial variability, Streams, Trophic structure, Populations
Experimental Design - SA012:
The diversity and environmental sensitivity of lotic invertebrates make them useful indicators of stream conditions; consequently macroinvertebrates have become increasingly popular in regional comparisons of streams (Hilsehoff 1988; Kerans and Kerr 1994; Rosenberg and Resh 1993). However, spatial and temporal variability in abundance and diversity among individual collections (at the reach scale) can make detection of differences among streams difficult (Norris and Georges 1993) necessitating some level of replication or physical compositing of samples. A dilemma we often face is how to determine the adequate number of samples. One approach has been to adjust the number of replicates to yield the desired level of precision (Elliott, 1977; Resh 1979); a criterion of ñ40% mean total abundances has been suggested as a practical goal (Resh and McElravy 1993; Pinder el al 1987). Another approach has been to evaluate the stability of the mean with increasing sampling effort (Elliott, 1977). These methods are limited by relying heavily on numerical abundance, with little regard for other assemblage attributes.
Our approach for assessing sampling adequacy was to consider a number of broadly representative metrics, and to identify appropriate levels of sampling effort to achieve stable values of these assemblage measures, somewhat analogous to one method suggested in Elliott (1977). Biomonitoring programs often use descriptors (often called metrics) designed to represent three basic assemblage characteristics: numerical abundance (total numbers of individuals), measures of diversity (taxa richness, diversity indices, and measures of evenness or dominance), and proportional abundances (proportions of total numbers including groups or taxa of special interest such as taxonomic order, dominant taxa, functional feeding groups or pollution-tolerant taxa). Some of these measures overlap, particularly those based on proportions that are all dependent on the same denominator, e.g. total abundance. We chose five metrics that represent different aspects of assemblage components: total abundance, taxa richness, Shannon diversity, proportional relative abundance of Ephemeroptera, Trichoptera and Plecoptera (EPT), and percent dominance of the most dominant taxon.
In the article associated with this study, our focus was on the adequacy of field macroinvertebrate sampling to discern differences among stream reaches within ecoregions. We greatly oversampled each stream reach, examining the incremental changes in metric values resulting from increases in sampling effort within each stream reach. This intense, hierarchical sampling design allowed us to quantitatively compare the relative magnitudes of macroinvertebrate assemblage metric variances across the range of spatial scales from within-habitat (eg. within a riffle) up to within-region (ie, comparing ecoregions).
Field Methods - SA012:
Site Selection : Two hand-picked stream sites (Lookout and Mack Creeks) in the H.J. Andrews Experimental Forest/Cascade Mt. Long-term Ecological Research area were also sampled to allow comparison to the large available database at these sites. Mack Creek is a small first order stream, Lookout Creek is a fairly large third order stream. The collection at these streams were added to 16 streams (9 Cascade and 7 Valley) that were sampled for macroinvertebrate assemblages as part of a larger study.
Field Sampling and Counting: Macroinvertebrate field sampling took place in late September, 1992. From the random start point on each stream, 14 study transects (cross-sections) were marked off upstream at 10 m intervals in small streams, and 25 m intervals in large streams. Three, one ft2 Surber samples, one on the right side, center and left were taken within each transect (Fig. 2). At least 7 transects of fast water habitat (riffles, rapids or cascades) and 7 transects of slow-water habitat (pools or glides) were sampled on each stream. If 7 of each habitat were not encountered after 14 transects, the crew continued upstream sampling at the same transect intervals in only the under-represented habitat until 7 were sampled. As a result, total number of transects varied from 14 to 20 per stream. Each macroinvertebrate sample was filtered through a 500 micro-meter soil sieve at stream side. Samples were placed in whirlbags and preserved in 70% ethanol. Stream habitat at each Surber sample location was qualitatively classified as either a pool, glide, riffle, rapid, or cascade.
Laboratory Methods - SA012:
Invertebrate samples were sorted and counted in the laboratory. At least 100 organisms, or all organisms, whichever count was achieved first, were enumerated for all samples. In 378 of the 449 samples, the entire sample was counted. If organisms were extremely dense or organic debris made enumeration very difficult the original sample was subsampled using a 0.5 m subsampler grid (Caton et al 1991). If subsampling was necessary, final counts were calculated by multiplying the observed count by the inverse of the proportion counted. Insect taxa,with the exception of Chironomidae, were identified to genus; Chironomidae were identified to tribe. Molluscs, Branchiopoda, and Copepoda were identified to family. Other invertebrate groups were identified to order. These taxa groupings were used in calculating metrics including taxa richness, and non-insectan taxa.
- SUPPLEMENTAL INFORMATION:
- Almost all assemblages were characterized by a log series abundance distribution . The number of new taxa added with increasing sample effort increased rapidly with the first 4-8 surber samples (500-1000 individuals counted), then increased more gradually. The number of new taxa added never reached zero even after counting more than 50 surber samples. Thus any measure of stream taxa richness is highly dependent on sampling effort. However, 6-9 samples captured a reasonable approximation of assemblage structure. Bootstrap analysis suggested between 65-87% of total taxa richness were described with nine samples. Stability in proportional measure values depend on the degree of dominance by one taxon, and generally stabilize between 5-10 samples in moderately diverse assemblages. A spatial analysis of variance showed differences between streams for all 5 metrics, indicating that within stream variability was not so large as to prevent detecting among stream differences. Within a stream, there was more variability among transects than within transects; this was also true for fast or slow water habitats analyzed separately. Overall, we caution against the use of protocols that sample less than 6 samples for assessing macroinvertebrate assemblages because of the excessive variability among small sample sizes and loss in assemblage structure information. We recommend a protocol of 6-9 samples spread out longitudinally along the sample stream.
- GENERAL TAXONOMIC COVERAGE:
- Ephemeroptera, Plecoptera, and Trichoptera
- TAXONOMIC SYSTEM:
- GEOGRAPHIC EXTENT:
- Mack Creek and Lookout Creek, Central Western Cascades of Oregon
- ELEVATION_MINIMUM (meters):
- ELEVATION_MAXIMUM (meters):
- MEASUREMENT FREQUENCY:
- PROGRESS DESCRIPTION:
- Study collection is completed and no new collection is planned
- UPDATE FREQUENCY DESCRIPTION:
- There are no plans to update these data
- CURRENTNESS REFERENCE:
- "Ground condition" is the range of dates during which the site was visited and data collected.