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    Spatial and environmental patterns of rare lotic macroinvertebrate diversity : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Manawatū, Palmerston North, New Zealand
    (Massey University, 2021) Rados, Dimitrios A.
    Stream macroinvertebrate communities comprise a few common taxa and many rare ones. Small populations of rare taxa can be more vulnerable to environmental change than those of common taxa. However, they are often discarded from community analyses on the grounds that they complicate data interpretation. The aim of this thesis was to evaluate the effect of rare taxa on assessing ecosystem health and on interpreting biodiversity patterns based on lotic macroinvertebrate communities. I assessed the effect of multiple types of rare taxa exclusion on biomonitoring, using macroinvertebrate data collected for the National River Water Quality Network of Aotearoa New Zealand. I compared the effect of different sampling methods on biodiversity patterns of rare taxa in pristine streams in the Tongariro National Park and determined the local environmental variables most strongly linked with common and rare taxa. Finally, I evaluated the effect dispersal processes and local environment have on structuring the common and rare components of lotic communities, considering the position within the stream network and the dispersal mode of the invertebrates. Exclusion of rare taxa led to significant misclassifications of ecological quality by biomonitoring tools that use presence-absence data, such as the Macroinvertebrate Community Index, and often masked their relationship with nutrient stressors. Different sampling methods collected clearly differentiated rare components of lotic assemblages, depending on the habitat sampled (riffles, non-riffles) and the life-stage of the invertebrates (benthic larvae, flying adults). A comprehensive species inventory can be compiled by combining methods, with benthic samples as the basis. Biodiversity metrics of the common and rare components of macroinvertebrate communities were related to similar environmental variables. While the structure of the two components was related to different variables, in combination they revealed a greater number of relationships with the environment. Rare taxa assemblages were not structured clearly by either local environment or dispersal processes, however their inclusion was necessary to demonstrate that the complete communities were determined by the local environment. Overall, I did not find any reason to exclude rare taxa from lotic macroinvertebrate studies, but rather found they can facilitate community analyses. Given the increasing threats on lotic macroinvertebrate biodiversity, it is also crucial to include them in such studies, hopefully so we can prevent their complete extinction.
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    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
    (Massey University, 2018) Dinh, Yen Thi Hai
    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.
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    Small stream ecosystems and irrigation : an ecological assessment of water abstraction impacts : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Palmerston North, New Zealand
    (Massey University, 2007) Dewson, Zoë Spence
    Small streams are often used for small-scale water abstractions, but the effects of these water abstractions on the instream environment, invertebrate communities and ecosystem functioning of small permanent streams is poorly understood. This research extends current knowledge by surveying existing water abstractions and completing flow manipulation experiments in the field. Reduced discharge often decreases water velocity, water depth, and wetted channel width and can increase sedimentation, modify the thermal regime and alter water chemistry. In a survey of sites upstream and downstream of existing water abstractions, I found that downstream sites had higher densities of invertebrates, but fewer taxa sensitive to low water quality compared with upstream sites. There were greater differences in physicochemical characteristics such as velocity and conductivity and in invertebrate communities between upstream and downstream sites on streams where a larger proportion of total discharge was abstracted. Using before-after, control-impact (BACI) designed experiments, weirs and diversions were created to experimentally decrease discharge by over 85% in each ot three small streams, ranging from pristine to low water quality. The response of invertebrates to short-term (one-month) discharge reduction was to accumulate in the decreased available area, increasing local invertebrate density. After a year of reduced flow, the density of invertebrates and percentage of mayflies, stoneflies and caddisflies decreased at the pristine site, whereas only taxonomic richness decreased at the mildly polluted stream. Reduced discharge had no affect on the invertebrate community at the stream with the lowest water quality. Reduced discharge had little influence on leaf decomposition rates, but distances travelled by released coarse particulate organic matter (CPOM) increased with increasing discharge. The effects of reduced discharge on primary production were not consistent between streams. Overall, the severity (magnitude/duration) of flow reduction appeared to influence invertebrate responses to water abstraction although the outcomes of water abstraction were dependent on the invertebrate assemblage present in each stream.