Multi-scaled environmental determinism of benthic invertebrate communities in braided rivers: evidence for complex hierarchical controls on local communities Duncan P. Gray* and Jon S. Harding 1 With 6 figures and 2 tables Abstract: 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 determi- nants 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 vari- ables 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 regu- lated 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 condi- tions, 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. Key words: invertebrates, braided river, spatial scale, environmental determinism, hierarchy, New Zealand. Authors’ address: 1 School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand 8140. * Corresponding author; email: duncan.p.gray@gmail.com Fundam. Appl. Limnol. Vol. 179/1, 3–15 Article Stuttgart, April 2011 © 2011 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany www.schweizerbart.de DOI: 10.1127/1863-9135/2011/0179-0003 1863-9135/11/0179-0003 $ 3.25 Introduction Understanding the relative importance of environmen- tal factors operating at differing spatial scales on the diversity and distribution of communities is one of the central themes of ecology (Allen & Starr 1982, Begon et al. 1996, Weins 1989). This knowledge is particu- larly pertinent in floodplain systems which are among some of the most imperiled on the globe (Ward et al. 1999). Regional species pools and factors that influ- ence dispersal provide a template for local diversity and community structure by determining the species available to colonise a particular location (Cornell & Lawton 1992, Ricklefs & Schluter 1993). Environ- mental conditions and species interactions then deter- mine the local species assemblage. However, the in- teraction between taxa and environmental conditions may occur across a range of scales or organisational levels, and correlations may exist between variables at different scales. Hence, taxa-environment relation- ships should be viewed as being hierarchical in struc- ture (Frissell 1986, Poff 1997). Assemblages within a habitat are the product of the species pool at a greater spatial scale and environmental conditions acting at