Title
The influence of pastoral and native forest land cover, flooding disturbance, and stream size on the trophic ecology of New Zealand streams
Author(s)
Fraley, Kevin M.;Warburton, Helen J.;Jellyman, Phillip G.;Kelly, Dave;McIntosh, Angus R.
Published
2021
Publisher
Austral Ecology
Abstract
Describing trophic structure within freshwater food webs can be a useful tool for understanding relationships to make ecological inferences and to inform management action. A complementary analysis examining both stable isotope (SI) and biomass community components may be useful, because these two responses may be influenced differently by habitat factors and perturbations (e.g. flooding disturbance). To test this, stable isotope‐derived trophic height and biomass were characterised, as was coarse allochthonous, periphyton, invertebrate and fish components, for 27 stream communities in Canterbury, New Zealand. Using piecewise structural equation modelling to test relationships between components, it was found that increased catchment agricultural land cover was associated with increased periphyton biomass and δ15N (trophic height) in stream invertebrates and invertivorous fishes, likely due to nitrate runoff, but did not affect piscivorous fishes. Additionally, native forest land cover was associated with increased instream allochthonous biomass. Increased discharge (i.e. larger habitat size) did not affect the trophic height or biomass per‐unit‐area of large‐bodied piscivorous fishes (non‐native trout and native eels), although it did result in decreased biomass of small‐bodied invertivorous fishes (primarily native benthic taxa), likely due to high water velocities in larger habitats rendering habitat less suitable for small‐bodied fishes. Finally, flooding disturbance negatively affected both trophic height and biomass of large‐bodied fishes, but did not affect small‐bodied invertivorous fishes. Overall, describing stream trophic structure with complementary SI and biomass structural equation models appears to be a useful approach for constructing an integrative picture of how abiotic and biotic habitat factors affect freshwater communities. Our findings indicate that land cover, stream size and flooding disturbance should be taken into consideration by stream managers when conducting habitat restoration efforts or setting fish harvest regulations.
Keywords
agricultural effects;community ecology;fish ecology;food webs;streams
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PUB25671