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Defining quantitative stream disturbance gradients and the additive role of habitat variation to explain macroinvertebrate taxa richness
Citation:
Ligeiro, R., R. Hughes, P. Kaufmann, D. Macedo, K. Firmiano, W. Ferreira, D. Oliveira, A. Melo, AND M. Callisto. Defining quantitative stream disturbance gradients and the additive role of habitat variation to explain macroinvertebrate taxa richness. ECOLOGICAL INDICATORS. Elsevier Science Ltd, New York, NY, 25:45-57, (2013).
Impact/Purpose:
Ligeiro and co-authors showed through their results that a reliable and comprehensive characterization of human pressures on streams relies on the use of different tools and should integrate data from different spatial scales. In their study, local and catchment disturbances were not correlated, and both independently affected site aquatic macroivertebrate assemblages. Their proposed methodology quantified the human pressure on sites without resorting to naturally varying habitat metrics. They demonstrated that the strength of the disturbance gradient influenced the degree to which natural habitat variability explained richness in macroinvertebrate taxa, a finding that has important implications for biomonitoring studies. The authors concluded that the use of quantitative disturbance gradients is essential for efficient use of ecological indicators and advised researchers to define quantitatively the disturbance status of their study sites. In this article, they outline a framework for doing so.
Description:
Most studies dealing with the use of ecological indicators and other applied ecological research relies on some definition or concept of what constitutes least-, intermediate- and most-disturbed condition. Currently, most rigorous methodologies designed to define those conditions are suited to large spatial extents (nations, ecoregions) and many sites (hundreds to thousands). The objective of this study was to describe a methodology to quantitatively define a disturbance gradient for 40 sites in each of two small southeastern Brazil river basins. The assessment of anthropogenic disturbance suffered by each site was based solely on measurements strictly related to the intensity and extent of anthropogenic pressures. We calculated two indices, one concerned site-scale pressures and the other catchment-scale pressures. We combined those two indices into a single integrated disturbance index (IDI) because disturbances operating at both scales affect stream biota. The local- and catchment-scale disturbance indices were weakly correlated (r = 0.21 and 0.35) and both significantly (p<0.05) reduced site EPT (insect orders Ephemeroptera, Plecoptera, Trichoptera) richness. The IDI also performed well for explaining EPT richness in the basin that presented the stronger disturbance gradient (R2 = 0.39, p<0.001). Natural habitat variability was assessed as a second source of variation in EPT richness. Stream size and microhabitats were the key habitat characteristics not related to disturbances that enhanced the explanation given by the IDI to EPT richness. In both basins the IDI plus habitat metrics together explained around 50% of EPT richness variation. In the basin with the weaker disturbance gradient, natural habitat explained more variation in EPT richness than did the IDI, which has implications for biomonitoring studies. We conclude that quantitatively defined disturbance gradients offer a reliable and comprehensive characterization of anthropogenic pressure that i
