Using Aquatic Macroinvertebrates as Indicators of Stream Flow ...

that some studies have found similar diversity in perennial and intermittent streams (Bottorff &Knight, 1988; Delucchi, 1988; Miller & Golladay, 1996; Shivoga, 2001; Price et al., 2003).Results for the density of organisms in different classes of stream may also differ; Miller &Golladay (1996) found that total invertebrate density was consistently about twice as high inperennial streams, but other studies have found greater invertebrate densities in intermittentstreams, as the drying process reduces and fragments wetted habitat, leaving remaining poolscrowded with surviving organisms (Boulton & Lake, 1992b; Stanley et al., 1994). Conflictingresults may be due to the fact that intermittent streams can have greater taxa richness or diversityduring periods of high flow, when the habitat is more similar to a perennial stream, but thenumber of taxa decreases as the stream dries down and organisms die, migrate, or take refuge(Boulton, 2003).Invertebrate abundance and diversity in temporary streams can also decrease following floodsthat scour out occupied habitat (Wright et al., 1984; Stanley et al., 1994; Miller & Golladay,1996). Fritz & Dodds (2005) found that intermittent prairie streams experiencing harsherconditions, including a long dry period, low flow predictability, high flood frequency, and/or lowsurface connectivity, had consistently lower taxa richness. This suggests that sites may varyannually in richness depending on differences in precipitation patterns (i.e. drought years vs.flood years). In addition, the drying regime in intermittent streams is affected by the types ofhabitat available; for example, intermittent streams with exposed bedrock channels retain fewermoist pools and seeps that could serve as refugia during the dry phase than intermittent streamswith abundant gravel, cobble, or woody debris (Clifford, 1966; Chadwick & Huryn, 2007).Although streams with differing flow duration often have many species in common, a smallsubset of taxa may predominate in either the perennial or intermittent system. SpanishMediterranean streams with different flow categories showed distinct biological differences, withintermittent streams dominated by taxa with pool-like strategies and ephemeral streamsdominated by taxa with life-history adaptations for surviving floods and droughts (Bonada et al.,2007). Taxa in permanent streams in this study exhibited few significant biological traits, mostlikely due to greater habitat stability (i.e. continuing presence of both riffles and pools), andperennial and intermittent streams had similar taxa richness, although both exhibited greaterrichness than ephemeral sites (Bonada et al., 2007). It should be noted that even whenintermittent and perennial streams are observed to have similar abundance and diversity of majortaxonomic groups, less similarity is seen when species-level identifications are made (Bottorff &Knight, 1988; Wood et al., 2005), although this level of taxonomic resolution is not alwayspossible.Community compositionA positive relationship has been noted between the proportion and/or abundance of EPT taxa andincreasing flow permanence (Feminella, 1996; Smith et al. 2003; Wood et al., 2005). This is notsurprising, as these orders are known in general to require cold, well-oxygenated, fast-flowingwater (Merritt et al., 2007; Wiggins, 1996; Stewart & Stark, 2002). However, some taxa in theseorders possess adaptations that render them more tolerant of temporary and/or slow-movingwaters. Several species within these three orders have been found in temporary streams, in someinstances as dominant components of the invertebrate community (Lehmkuhl, 1971; Tew, 1971;Macroinvertebrates as indicators of stream flow duration,The Xerces Society for Invertebrate Conservation7