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Contrasting trophic-cascade effects driven by variation in morphology of the perches used by a larval damselfly
Freshwater Biology, Volume: 61, Issue: 5, Pages: 693 - 701
Swansea University Author: John Griffin
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DOI (Published version): 10.1111/fwb.12739
1. The presence of habitat structures (e.g. caves, ledges, branches) has well-documented ecologicaleffects. However, it remains largely unknown how variation in the morphology of particular habitatstructures affects ecological interactions.2. Using an algae–cladoceran grazer–larval damselfly food ch...
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1. The presence of habitat structures (e.g. caves, ledges, branches) has well-documented ecologicaleffects. However, it remains largely unknown how variation in the morphology of particular habitatstructures affects ecological interactions.2. Using an algae–cladoceran grazer–larval damselfly food chain as a model in a series of microcosmexperiments, we manipulated food-chain length and the length (long versus short) and diameter(thick versus thin) of vertically orientated damselfly perches (habitat structure) and examined thedensity of the grazers and algae. Because the larval damselflies are usually more flexible on thinnerperches and have broader foraging domains on longer perches, we predicted that when on long andthin perches they would suppress grazer density more efficiently and hence confer a more positivetrophic-cascade effect on algal growth.3. As predicted, larval damselflies occupying long and thin perches most strongly reduced grazerdensity and increased algal density, illustrating a positive trophic cascade. In all other damselflytreatments, and despite reduced grazer density, algal density declined, showing a negative trophiccascade due to an elevation in grazer foraging efficiency under predation risk. This probably resultedfrom the increased activity of the grazers and their spatial shift to the lower water column wherealgal density was higher.4. In conclusion, perch morphology affected the direction and strength of the trophic cascade byaltering both density-mediated and behaviour-mediated indirect interactions. Considering thatanthropogenic disturbance is dramatically changing the morphological diversity of habitat structures,we call for more research into the ecological consequences of such physical diversity at communityand ecosystem levels.
algae–cladoceran–damselfly, habitat structures, morphology, species interaction, trophic cascade
Faculty of Science and Engineering