ASSESSING INVERTEBRATE RESPONSES TO HUMAN ACTIVITIES - EVALUATING ALTERNATIVE APPROACHES

The goal of biological monitoring is to evaluate the effect of human a ctivities on biological resources. Ln this Study, ive linked human act ivities across landscapes to specific changes in assemblages of benthi c macroinvertebrates in streams that drain those landscapes. We used d ata from 2nd- to 4th-order streams in southwestern Oregon to test appr oximately 30 hypotheses about how macroinvertebrates respond to severa l common human actions, especially logging and associated road constru ction. We found 10 attributes of macroinvertebrate assemblages to be r eliable indicators of disturbance. Data from a subsequent year confirm ed those results. We used simple graphical methods to evaluate land-us e data and to relate the data to observed responses of invertebrates. We constructed a multimetric index (benthic index of biological integr ity, or B-IBI) from component metrics that distinguished disturbed str eam sites from minimally disturbed sites. Using an independent data se t, we found that B-IBI scores were significantly lower for streams who se watersheds were more degraded by human activities. We also tested r apid bioassessment protocol (RBP) III as modified by Oregon Department of Environmental Quality. REP III failed to detect differences among sites that B-IBI did detect. Because biologists continue to debate the relative merits of a multimetric vs. a multivariate approach for inte rpreting biomonitoring data, we also used principal components analysi s (PCA) to explore patterns in our multidimensional data. We chose PCA based on species abundance because it has been the most common techni que used by state and federal agency biologists to interpret biomonito ring data. PCA failed to detect clear differences in our data set (e.g ., between most and least disturbed sites). We suggest that multivaria te statistical analyses are most appropriate for exploratory analysis when the investigator has limited knowledge of an ecological system an d wants to generate testable hypotheses. We demonstrate that sufficien t information about the natural history of stream invertebrates is ava ilable to support more direct tests of how invertebrates respond to hu man disturbance ?he components of a good multimetric index are founded on tested hypotheses and thus provide a sound scientific assessment o f a stream site. We argue that a method that incorporates ecological i nformation is more suitable for biomonitoring than one relying on stat istical algorithms.