QUANTIFYING DISTURBANCE IN STREAMS - ALTERNATIVE MEASURES OF DISTURBANCE IN RELATION TO MACROINVERTEBRATE SPECIES TRAITS AND SPECIES RICHNESS

Appropriate tests of disturbance theory require that disturbance is de fined and measured in an organism-related sense. We quantified 7 measu res of disturbance, 3 dealing with the pattern of disturbance of the s tream bed (assessed using painted tracer particles), 3 dealing with as pects of discharge variation and 1 being a subjective composite measur e of stream channel stability (Pfankuch's index). Hypotheses relating to invertebrate taxon richness (maximal at intermediate levels of dist urbance) and the representation of particular insect species traits (a ssemblages in more disturbed sites contain higher percentages of indiv iduals possessing high adult mobility and streamlined-flattened larval morphology) were both supported when disturbance was measured in term s of bed movement but generally not when measured in terms of discharg e variation. When disturbance was estimated by Pfankuch's index, speci es trait predictions were supported but the taxon richness prediction was not. A co-inertia analysis, searching for a co-structure between o ur environmental and faunistic data sets, allowed us to distinguish ta xa that apparently are resistant to bed movement from tara that appear to be resistant to flow variations; this more detailed analysis indic ates that the most appropriate measure of disturbance may vary even am ong quite closely related taxa. The construction of a comprehensive th eory of disturbance in streams requires that disturbance is quantified in a way that allows both multi-site and multi-study comparisons. The painted-particle approach, described here, has the potential to permi t such standarized comparative studies.