Disturbance and the community structure of stream invertebrates: patch‐specific effects and the role of refugia

Abstract

1.We have previously shown that the impact of spates on stream invertebrates may differ among patches separated by distances of metres or less. Here we analyse the species-specific flood responses of larval chironomids and adult and near mature copepods living in different patch types. Four patch types (with eight replicates of each) were compared: the sandy mid-channel, fine sediments around dams, coarse sediments around dams, and dam debris. Additionally, since some fine sediment patches had been shown previously to act as flow refugia while others did not, we also examined speciesspecific responses in refugium vs. non-refugium fine sediment patches. Detrended correspondence analysis was used to test for changes in assemblage structure (species composition and relative abundance). 2. Species richness was not altered in a predictable manner by floods; the least stable patch types (mid-channel and coarse patches) did not necessarily show reduced species richness during the spate. 3. As indicated by the spread of DCA ordination scores, there was generally a high degree of overlap in the species composition among the four patch types. Nevertheless, copepod species composition and relative abundance were more similar among patch types during the spate than pre-spate. Spates may induce a re-distribution of copepod species among the patch types. Chironomid species composition and relative abundance were no more similar among patch types during the spate than pre-or post-spate. 4. For both chironomids and copepods, species composition and relative abundance (as assessed by DCA ordination scores) in refugium patches changed more in response to the spate than in the non-refugium patches. An influx of individuals from just a few species for each group was responsible for the change in assemblage structure. Thus, despite the fact that our past work has shown that refugia may confer enhanced resistance and resilience of copepod and chironomid assemblages in terms of total faunal abundances, the present work suggests that resistance and resilience of the species composition of the community apparently are no greater in refugium patches than in nonrefugium patches.1995 BlackweU Science Ltd 343

Effects of a multi-year experimental flood regime on macroinvertebrates downstream of a reservoir

“…They observed some areas of the stream bed to be essentially unaffected by the high flows, whereas others were heavily scoured. This particular response has been observed by others studying the effects of floods on zoobenthos (Palmer et al, 1995;Matthaei et al, 1999a, b), and it is probable that the less disturbed areas act as refugia for macroinvertebrates during a flood (Francoeur et al, 1998). The second larger flood, in contrast, mobilized most of the stream bed and we observed few areas of the study reach that were left undisturbed.…”

Use of Random Amplified Polymorphic DNA (RAPD) to study genetic diversity within a population of blackfly, Simulium gravelyi from Palni hills, peninsular India

“…These factors are influencing diversity and abundance (e.g., Vinson & Hawkins 1998) and are scale dependent. At the scale of the reach, numerous factors are associated with species richness, including substrate heterogeneity (Cowie 1985), water chemistry (Townsend et al 1983;Jenkins et al 1984;Erman & Erman 1995), water temperature (Ward & Dufford 1979;Ward 1986), stream flow and size (Jenkins et al 1984;Erman & Erman 1995;Malmqvist & Eriksson 1995;Tate & Heiny 1995), disturbance (Erman & Erman 1995;Palmer et al 1995), and altitude (Tate & Heiny 1995).…”

Spatial and temporal patterns of benthic invertebrate communities in an intermittent river (North Africa)

“…Numerous studies have focused on the biological implications of these constraints in terms of processes and mechanisms (Palmer et al 1995, Palmer & Poff 1997, Townsend et al 1997. The community structure is changed by perturbations in the environment and the degree of structural change is used to assess the intensity of the environmental stress (Hellawell 1986).…”