Premise 9 - Biological Attributes

Click below to view some of the premises from Karr and Chu (1999).

Only a few biological attributes provide reliable signals about biological condition

FROM "Restoring Life in Running Waters" by James R. Karr and Ellen W. Chu. (Reprinted with permission from Island Press)

The success of biological monitoring programs and their use to define and enforce biological criteria is tied to identifying biological attributes that provide reliable signals about resource condition (Table 3). Choosing from the profusion of biological attributes (Figure 9) that could be measured is a winnowing process, in which each attribute is essentially a hypothesis to be tested for its merit as a metric. One accepts or rejects the hypothesis by asking, Does this attribute vary systematically through a range of human influence? When metrics are selected and organized systematically, an effective multimetric index can emerge.

Figure 9

Figure 9: Almost any biological attribute can be measured, but only certain attributes provide reliable signals of biological condition and therefore merit integration into a multimetric index.

Knowledge of natural history and familiarity with ecological principles and theory guide the definition of attributes and the prediction of their behavior under varying human influences. But successful biological monitoring depends most on demonstrating that an attribute has a reliable empirical relationship – a consistent quantitative change – across a range, or gradient, of human influence. Unfortunately, this crucial step is often omitted in many local, regional, and national efforts to develop multimetric indexes (e.g., RBP I, II, III; Plafkin et al. 1989).

The study of populations has dominated much ecological research for decades (see section II), so researchers still assume that population size (expressed as abundance or density) provides reliable signal about water resource condition. But because species abundances vary so much as a result of natural environmental variation, even in pristine areas, population size is rarely a reliable indicator of human influence (see Premise 14 and Premise 25). Large numbers of samples (>25) were required, for example, to detect small (<20%) differences in number of fish per 100 square meters of stream surface area in small South Carolina streams (Paller 1995b). Other attributes – such as taxa richness (number of unique taxa in a sample, including rare ones) and percentages of individuals belonging to tolerant taxa – have, in contrast, been found to vary consistently and systematically with human influence. Such attributes, when graphed, give rise to analogues of the toxicological dose-response curve – which we call ecological dose-response curves – where the y-axis represents the measured attribute and the x-axis, measures of human influence (Figure 10).

Figure 10

Figure 10. Average taxa richness of Plecoptera and sediment-intolerant taxa plotted against riparian condition for seven stream sites in the John day Basin, Oregon. Site A had fewer taxa than expected because although cattle were excluded, intense grazing upstream had affected the site's biota.

Ecological dose-response curves differ in one critical respect from toxicological dose-response curves. Toxicological dose-response curves usually measure biological response in relation to dose of a single compound. Ecological dose-response curves measure a biological response to the cumulative ecological exposure, or "dose," of all events and human activities within a watershed, expressed in terms such as percentage of area logged, grazing intensity, or percentage of impervious area. The number of native fish species in a midwestern stream sampled today, for example, reflects the cumulative effects of natural events and human influence up to the present. The very existence of those species is the product of what has occurred before.

References

Paller, M. H. 1995b. Interreplicate variance and statistical power of electrofishing data from low-gradient streams in the southeastern United States. N. Am. J. Fish. Manage. 15: 542-550.

Plafkin, J. L., M. T. Barbour, K. D. Porter, S. K. Gross, and R. M. Hughes. 1989. Rapid bioassessment protocols for use in streams and rivers: Benthic macroinvertebrates and fish. EPA/440/4-89-001. Assessment and Water Protection Division, US Environmental Protection Agency, Washington, DC.