Impact of simulated drought on ecosystem biomass production: an experimental test in stream mesocosms

Authors

  • MARK E. LEDGER,

    1. School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
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  • FRANCOIS K. EDWARDS,

    1. School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
    2. Centre for Ecology and Hydrology, Maclean Building, Benson Lane, Crowmarsh Gifford, Wallingford OX10 8BB, UK
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  • LEE E. BROWN,

    1. School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
    2. School of Geography, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK
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  • ALEXANDER M. MILNER,

    1. School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
    2. Institute of Arctic Biology, University of Alaska, Fairbanks, Alaska 99775, USA
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  • GUY WOODWARD

    1. School of Biological and Chemical Sciences, Queen Mary, University of London, London E1 4NS, UK
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Dr Mark Ledger, tel. +44 121 414 5540, fax +44 121 414 5528, e-mail: m.e.ledger@bham.ac.uk

Abstract

Climate models predict widespread shifts in precipitation patterns and increases in the frequency of extreme events such as droughts, but consequences for key processes in affected ecosystems remains poorly understood. A 2-year manipulative experiment used a series of stream mesocosms to test the effect of recurrent drought disturbance on the composition and secondary production of macroinvertebrate consumer assemblages and functional groups. On average, secondary production in drought-disturbed communities (mean 4.5 g m−2 yr−1) was less than half of that that in controls (mean 10.4 g m−2 yr−1). The effects of the drought differed among functional feeding groups, with substantial declines for detritivore shredders (by 69%) and engulfing predators (by 94%). Contrasting responses were evident among taxa within most functional feeding groups, ranging from extirpation to irruptions in the case of several small midge larvae, but production of most species was suppressed. Taxon-specific responses were related to body mass and voltinism. The ratio of production to biomass (community P/B) increased under drought, reflecting a shift in production from large long-lived taxa to smaller taxa with faster life cycles. This research provides some of the first experimental evidence of the profound effects that droughts can have on both the structure and functioning of aquatic ecosystems.

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