Table 4-19. Thresholds defining expectations of indicator and metrics under 

 minimal human disturbance 



Expected conditions based on large number of sample sites, as opposed to a set of 

 defined "reference" sites (Simon and Lyons 1995). 



Expectations for metrics based on number of species calibrated for stream size or type 

 (watershed area, gradient, cold vs. warm water) (Fausch et al. 1984). 



Taxonomic composition and abundance metrics 



• Number of native species: Varies with watershed area 



• Number of native families: Varies with watershed area 



• Total Abundance: s500 individuals collected in standard effort sample 

 Indicator species metrics: 



• Percent of non-native individuals: 0% 



• Sensitive spp. richness: Varies with watershed area 



• Percent tolerant individuals:<20% 

 Habitat metrics 



• Number of benthic species: Varies with watershed area 



• Number of water column species: Varies with watershed area 

 Trophic metrics 



• Numberof trophic strategies: 1 to 5 (varies with watershed area) 



• Percent individuals as carnivores: >5% 



• Percent individuals as invertivores: s50% 



• Percent individuals as omnivores: <20% 



• Percent individuals as herbivores: <10% 

 Reproductive guild metrics 



• Number of reproductive strategies: 1 to 4 (varies with watershed area) 



• Percent individuals as tolerant spawners: s 20% 



Table 4-20. Threshold values for classifying condition 



Range of indicator values = 1 to 100 

 Excellent: > 85 

 Acceptable: 70 to 85 

 Marginal: 50 to 69.9 

 Impaired: < 50 



Summary 



The approach to defining expected conditions for individual metrics under a regime of minimal human 

 disturbance is presented, and is based on standard documented approaches established for other multimetric 

 indicators. Thresholds for the final indicator score are proposed for four classes of ecological condition. 

 These thresholds are consistent with the potential capability of the indicator to distinguish among condition 

 states, and with schemes developed for similar multimetric indicators. Additional research on the expectation 

 for individual metrics remains, subsequent to achieving a better understanding of indicator responsiveness. 

 These threshold values should be confirmed, either empirically through application to sites representing a 

 known range of impairment, and/or through peer review by professional ecologists and resource managers. 



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