The effects of hydrological and nutrient disturbance on stream invertebrate communities using a trait-based approach : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Aquatic Ecology at Massey University, Manawatu, New Zealand

Anthropogenic altered flow regimes and nutrient enrichment can cause significant impacts on stream biota and may lead to species loss if characteristics of the local fauna are not compatible with the new environmental conditions. I used fourth corner models, Bayesian ordination, and regression analysis to assess those potential effects on trait and species composition of invertebrate communities in UK, New Zealand (NZ) and Vietnamese streams. NZ temperate mountain streams with greater substrate disturbance increased the abundance of plastron- respirers, but not those having two aquatic life stages or who were filter feeders. UK temperate rivers with predictable multiple high flows per year supported individuals having highly synchronized life history strategy; rivers with one prolonged rising climb and strong groundwater influence were better for those having a high reproduction strategy, and rivers with a steep peak flow supported both strategies. Nutrients affect functional feeding and life history traits via promoting algal overgrowth in NZ streams. Both periphyton biomass and nutrients increased the abundance of algae piercers, collectors and those having two aquatic life stages, being long-lived and having hermaphroditic ability; but decreased the abundance of shredders, scrapers, and those having univoltine life cycles. The post-flood recovery of invertebrate communities depended on the recovery of the food base of the food web that was, in turn, determined by the presence of a forest canopy cover and nutrient levels in a stream. Within the forest canopy stream, communities in the low nutrient site recovered by week 9 after a 1-in-50-year flood in Wellington, NZ. Without the forest canopy, the recovery of communities in nutrient impacted streams (by 25 weeks) was probably associated with a quicker regrowth of periphyton while communities in the low nutrient site had not recovered even after 40 weeks. Hydrological disturbances, nutrients, and their combination had strong effects on invertebrate communities in temperate streams. Taxa that survive in a site have trait characteristics that are highly compatible with both the hydrological and nutrient conditions at a site. In contrast to temperate invertebrate communities, Vietnamese tropical highland community structure was influenced more by elevation than disturbance. Further studies are required to clarify how flow disturbance may effect invertebrate communities in tropical streams