Multi-scaled environmental determinism of benthic invertebrate communities in braided rivers: evidence for complex hierarchical controls on local communities

Globally many braided river systems have become highly modified, however in their natural state they include a wide range of habitats that support high benthic invertebrate diversity. Here we investigate the determinants of this diversity by assessing the influence of environmental variables on invertebrate communities across eleven braided rivers in New Zealand. Within each river, six reaches were sampled and within each reach up to five floodplain habitat types (main channels, side braids, spring sources, spring creeks and ponds). Environmental variables either measured in the field or derived from GIS and hydrological data bases were compared to invertebrate distributions. Communities in all habitat types were influenced by catchment scale hydrology, which partially regulated factors at lesser scales. However, the spatial scale of environmental factors with the greatest influence varied between habitat types. Main channel communities were influenced equally by catchment and habitat scale conditions, whereas spring communities were primarily regulated at the habitat level. There was considerable cross-scale correlation in the effect of environmental factors suggestive of complex hierarchical controls. Invertebrate diversity was regulated by the environment across a range of scales. Programs concerned with the conservation of braided river systems should incorporate this hierarchical environmental determinism within catchments and acknowledge the value of lateral floodplain habitats.