Drought intensification alters the composition, body size, and trophic structure of invertebrate assemblages in a stream mesocosm experiment

Research output: Contribution to journalArticlepeer-review


  • Thomas W. H. Aspin
  • Kris Hart
  • Matthew J. O'callaghan
  • Mark Trimmer
  • Zining Wang
  • Gavin M. D. Williams
  • Guy Woodward

External organisations

  • School of Geography, Earth and Environmental SciencesUniversity of Birmingham Birmingham UK
  • Wessex Water Bath UK
  • Institute of Arctic BiologyUniversity of Alaska Fairbanks Alaska
  • School of Biological and Chemical ScienceQueen Mary University of London London UK
  • Department of Life SciencesImperial College London Ascot UK


Predicted trends towards more intense droughts are of particular significance for running water ecosystems, as the loss of critical stream habitat can provoke sudden changes in biodiversity and shifts in community structure. However, analysing ecological responses to the progressive loss of stream habitat requires a continuous disturbance gradient that can only be generated through large‐scale manipulations of streamflow. In the first experiment of its kind, we used large artificial stream channels (mesocosms) as analogues of spring‐fed headwaters and simulated a gradient of drought intensity that encompassed flowing streams, disconnected pools, and dry streambeds. We used breakpoint analysis to analyse macroinvertebrate community responses to intensifying drought, and identify the taxa and compositional metrics sensitive to small changes in drought stress. We detected breakpoints for >60% of taxa, signalling sudden population crashes or irruptions as drought intensified. Abrupt changes were most pronounced where riffle dewatering isolated pools. In the remnant wetted habitat, we observed a shift to larger body sizes across the community, primarily driven by irruptions of predatory midge larvae and coincident population collapses among prey species (worms and smaller midges). Our results suggest that intense predation in confined, fragmented stream habitat can lead to unexpected changes in body sizes, challenging the conventional wisdom that droughts favour the small. Pool fragmentation might thus be the most critical stage of habitat loss during future droughts, as the point at which impacted rivers and streams begin to exhibit major shifts in fundamental food web properties.


Original languageEnglish
Pages (from-to)750-760
Number of pages11
JournalFreshwater Biology
Issue number4
Publication statusPublished - 1 Apr 2019


  • disturbance gradient, drying, macroinvertebrates, predation, stream drought