Abstract
Strategies for the coexistence of two caddisflies,Aoteapsyche raruraru and A. colonica(Trichoptera: Hydropsychidae) were considered in aSouth Island lake outlet, New Zealand. Three mainstrategies were assessed, firstly that competitionbetween species may be reduced by the presence ofselective predators, secondly, that coexistence ismaintained by periodic disturbance which reducescompetition effects, and thirdly that interspecificcompetition is negated by segregation of either lifehistories or feeding strategies, and diet ormicrohabitat preferences. The first strategy wasrejected, as gut analyses of common fish andmacroinvertebrate predators showed that both speciesof Aoteapsyche were taken in approximately equalproportions to their benthic densities (i.e. 10:1 A. raruraru to A. colonica), indicating thatpredation was unlikely to influence coexistence.Similarly the second strategy was not supported byobservations of flow conditions during the study whichwere insufficient to move the substrata extensivelycolonised by both species of Aoteapsyche.Finally, temporal segregation of life histories wasnot observed, but analyses of larval guts indicatedthat diet was affected by shelter location on thesubstrate. Sampling of substrate microhabitats showedthat A. raruraru larvae occurred on the uppersurfaces, sides and under surfaces of large cobbles,although significantly higher densities were collectedfrom the upper surfaces and sides. In contrast, A. colonica aggregated on the sides and undersurfacesof cobbles. In other streams A. colonica showsa similar microdistribution but in a silted streamlacking seston, and in the absence of A. colonica, A. raruraru larvae occurred mainly onthe under surfaces of stones. Co-existence of thesetwo congeners would seem to be possible bymicrohabitat segregation where food availability ishigh, however in the absence of a plentiful foodsupply and A. colonica the microdistribution ofA. raruraru may differ.
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Harding, J.S. Strategies for coexistence in two species of New Zealand Hydropsychidae (Trichoptera). Hydrobiologia 350, 25–33 (1997). https://doi.org/10.1023/A:1003012512998
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DOI: https://doi.org/10.1023/A:1003012512998