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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Disturbance Ecology III
DISTURBANCE HISTORY AND STABILITY OF MACROINVERTEBRATE COMMUNITIES IN EXPERIMENTAL STREAMS.
R.M.L. Harris1,2, M.E. Ledger1,2, A.M. Milner1, and P.D. Armitage3. 1School of Geography and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, U.K., 2Freshwater Biological Association, U.K., 3Centre for Ecology and Hydrology Dorset, Winfrith Technology Centre, Winfrith Newburgh, Dorchester, Dorset, U.K. DT2 8ZD
Biological traits such as high mobility and growth rate convey high resilience to stream macroinvertebrate populations, enabling them to recover rapidly from disturbance. Where disturbance episodes are frequent and severe, recovery may be incomplete, and directional change in community composition could then occur. We investigated whether macroinvertebrate communities in stream channels exhibited stability or directional change in response to contrasting disturbance regimes imposed over a 21-month experiment. Four replicate channels were subjected to one of three treatments; 1) monthly disturbance (5 day dewatering episode); 2) three monthly disturbance; 3) undisturbed (Control). We found that dewatering disturbance reduced taxa richness and invertebrate abundance in all channels. Early in the experiment, chironomids (Tanytarsini) and oligochaetes (Tubificidae) exploited space created by these events, but as the number of disturbance episodes accrued though time, their populations were strongly reduced. These trends reflected the overall pattern of community change in disturbed channels, where species richness and abundance declined as experimental time progressed. Repeated comparisons of disturbed communities with contemporaneous controls revealed an overall directional change in the community structure of the disturbed channels over time. We conclude that disturbance history can influence the composition of communities dominated by highly mobile species.
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