Comparison

The use of abundance-weighted pollution tolerance scores in the BRI is comparable to the use of feeding modes as a measure of pollution tolerance in the infaunal trophic index (ITI), an index extensively used in the southern California area. BRI utilizes an empirical approach in order to elaborate pollution tolerance scores for individual species, instead of extrapolating pollution tolerance from the feeding mode. In spite of variances in methodology, an important relationship was discovered between the ITI species scores and values applied to individual species. When differences do arise, they can typically be attributed to a lack of information about the feeding mode of a species. The southern California study has confirmed that p¡ values can vary significantly among members of the same family.

The second fundamental variation between the BRI method and the ITI is that, when external (noncalibra-tion) data from outfall monitoring programs was utilized, it was observed that the ITI uses an average of approxi mately 50% of the species in a sample, while the BRI utilizes 84%. The use of a smaller amount of species (along with the use of untransformed abundance weights) makes the ITI subject to higher variation in the abundances of individual species. The correlation for the ITI presented the greatest reduction when the single most abundant species was eliminated, which signifies that a single abundant species is capable of having a significant effect on ITI values.

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