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Presented at the NABS Annual meeting, Vancouver, British Columbia, 2004
in Bioassessment 4
Examining rarity in a macroinvertebrate bioassessment database
D.B. Arscott, E.B. Kratzer, J.K. Jackson, C.L. Aufdenkampe, C.L. Dow, L.A. Kaplan, and B.W. Sweeney. Stroud Water Research Center, Avondale, PA 19311
Macroinvertebrate rarity from a three-year, 60 site, biomonitoring effort in New York City water supply watersheds was examined to (1) quantify relationships between rarity, abundance, and richness; (2) compare rarity along impact gradients; and (3) determine the contribution of rare taxa to community responses along impact gradients. Integrated quantitative sampling (Surber; 250um mesh) yielded 543 taxa generally identified to genus/species including chironomids. Several approaches to defining rare taxa (frequency of occurrence in time [1 in 3 years] or space [restricted distribution], and abundance [scarcity]) were used to classify taxa and employ metric (total/EPT richness, density) and multivariate (NMDS and Co-Inertia Analysis) analyses. Of the 543 taxa, 175 (32%) were found at 3 or fewer sites and 536 (99%) were found to be occasional (1 in 3 years) in at least one site out of 60. Rarity correlated positively with richness and negatively with total abundance. Severe impact gradients (toxic and high organics) had a negative effect on rare taxa, while moderate impact gradients (non-point nutrients) did not correlate with rarity. Indirect (NMDS) and direct (Co-Inertia) gradient techniques suggest that rare taxa revealed impact gradients similar to common taxa and can result in improved explanatory power along moderate impact gradients.
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