Taylor's Law improves the accuracy of bioassessment: an example for freshwater macroinvertebrates

Abstract

Legislation obliging the maintenance of ecologically defined quality standards has focused attention on the accuracy of bioassessment metrics. Describing the statistical distribution of ecological indicators, Taylor’s Law (TL) has important relevance to the design and interpretation of bioassessment protocols. Analyzing a detailed UK dataset revealed that most macroinvertebrate indicators were characterized by similar geometric distributions, providing a theoretical imperative to log-transform indicator abundance prior to metric derivation. Evaluating a range of bioassessment metrics revealed a 2–4 fold increase in precision and up to 50% improvement in fidelity compared to standard assessment metrics, based on raw-abundance data. Similar improvement in metric fidelity for North American rivers (up to 60%) indicates the broad biogeographic relevance of this analytical modification. Reducing the risk of misclassifying biological quality for a suite of environmentally contrasting rivers from 80% to 4% emphasizes the benefit that this application of TL could deliver to river management. Requiring no increase in costs and with the potential for retrospective application to historical data, this simple modification is entirely compatible with contemporary assessment practice.