Food webs from the Lerderderg River, an intermittent stream in Victoria, Australia, were compiled with the aim of examining changes in food web structure in a highly variable habitat. Emphasis was placed on a high degree of taxonomic precision. Spatial and temporal variation in the food webs was assessed by partitioning the study area into three sites, located ≈1.5 km apart along the river. Sites differed in overall stream width and the length of the low streamflow period during summer. Three separate webs for each site were compiled for four different times of the year. Relatively little spatial variation in community structure was observed. In contrast, temporal variation was considerable, with species composition and the number of species in the community changing considerably over the year. The number of species increased dramatically as the period of constant streamflow lengthened. Detritivores dominated the community, both in terms of species and individual numbers. The proportion of predators in the community increased slightly by the end of the year, suggesting that recolonization of the community by predators lags behind that of detritivores. The increase in the number of predator species also resulted in an increase in the mean food chain length through the year. Patterns observed in the food webs tended to fall within the range of values reported from several previous studies, suggesting that underlying constraints may structure certain aspects of food webs. However, the constancy of certain food web statistics was attributable either to methodological decisions made during compilation, or to an inherent property of the statistic itself. The potential sensitivity of several food web statistics to the methodology used to compile a food web render between—web comparisons difficult due to the confounding effects of methodology. This suggests that comparisons between food webs should be restricted to webs derived from similar habitats using a comparable methodology.

Summary1. Some native fish in New Zealand do not coexist with introduced salmonids. Previous studies of disjunct distributions of exotic brown trout Salmo trutta and native galaxiids demonstrated native extirpation except where major waterfalls prevented upstream migration of trout. In the Manuherikia River system, we predicted that water abstraction might be a further factor controlling the spatial distribution of both the invader and a native fish. 2. We applied multiple discriminant function analyses to test for differences in environmental conditions (catchment and instream scales) at sites with roundhead galaxias Galaxias anomalus and brown trout in sympatry and allopatry. We then used a supervised artificial neural network (ANN) to predict the presence-absence of G. anomalus and brown trout (135 sites). The quantification of contributions of environmental variables to ANN models allowed us to identify factors controlling their spatial distribution. 3. Brown trout can reach most locations in the Manuherikia catchment, and often occur upstream of G. anomalus . Their largely disjunct distributions in this river are mediated by water abstraction for irrigation, together with pool habitat availability and valley slope. Trout are more susceptible than the native fish to stresses associated with low flows, and seem to be prevented from eliminating galaxiid populations from sites in low gradient streams where there is a high level of water abstraction. 4. Synthesis and applications . In contrast to many reports in the literature, our results show that hydrological disturbance associated with human activities benefits a native fish at the expense of an exotic in the Manuherikia River, New Zealand. Water abstraction is also known to have negative impacts on native galaxiids, therefore we recommend restoring natural low flows to maintain sustainable habitats for native galaxiids, implementing artificial barriers in selected tributaries to limit trout predation on native fish, and removing trout upstream.

1. Hypoxic conditions occur frequently during hot, dry summers in the small lentic waterbodies (billabongs) that occur on the floodplains of the Murray-Darling River system of Australia. Behavioural responses to progressive hypoxia were examined for the native and introduced floodplain fish of the Ovens River, an unregulated tributary of the Murray River in south-east Australia. 2. Given the high frequency of hypoxic episodes in billabongs on the Ovens River floodplain, it was hypothesised that all species would exhibit behaviours that would confer a degree of hypoxia-tolerance. Specifically, it was hypothesised that as hypoxia progressed, gill ventilation rates (GVRs) would increase and aquatic surface respiration (ASR) would become increasingly frequent. Fish were subjected to rapid, progressive hypoxia from normoxia to anoxia in open tanks. 3. All tested species exhibited behaviours consistent with their use of potentially hypoxic habitats. As hypoxia progressed, GVRs increased and all species, with the exception of oriental weatherloach, began to switch increasingly to ASR with 90% of individuals using ASR at various oxygen concentrations below 1.0 mg O 2 L )1 . Australian smelt, redfin perch and flat-headed galaxias were the first three species to rise to ASR, with 10% of individuals using ASR by 2.55, 2.29 and 2.21 mg O 2 L )1 respectively. Goldfish and common carp were the last two species to rise to ASR, with 10% of individuals using ASR by 0.84 and 0.75 mg O 2 L )1 respectively. In contrast to other species, oriental weatherloach largely ceased gill ventilation and used air-gulping as their primary means of respiration during severe hypoxia and anoxia. 4. Australian smelt, redfin perch and flat-headed galaxias were unable to maintain ASR under severe hypoxia, and began exhibiting erratic movements, termed terminal avoidance behaviour, and loss of equilibrium. All other species continued to use ASR through severe hypoxia and into anoxia. Following a rise to ASR, GVRs either remained steady or decreased slightly indicating partial or significant relief from hypoxic stress for these hypoxia-tolerant species. 5. Behavioural responses to progressive hypoxia amongst the fish species of the Ovens River floodplain indicate a generally high level of tolerance to periodic hypoxia. However, species-specific variation in hypoxia-tolerance may have implications for community structure of billabong fish communities following hypoxic events.

Summary Amphidromy is a widespread migratory behavioural syndrome exhibited by fish (and some aquatic invertebrates) that spawn in fresh water and whose larvae migrate to pelagic marine (or lentic) habitats for a period of early growth, followed by a return migration to adult freshwater habitats. The fitness advantage of amphidromy has been the subject of prolonged debate, and we examined the hypothesis that amphidromy mainly increases fecundity through the production of small pelagic larvae. We compared egg size (a proxy for larval size) of closely related non‐migratory and amphidromous fish species in the families Cottidae, Galaxiidae, Eleotridae and Gobiidae. To examine how egg size changes in relation to body size within a taxonomic group, we also compared egg size and maximum body size across most species of New Zealand non‐migratory and amphidromous galaxiids. Non‐migratory species generally have relatively larger eggs than their amphidromous confamilial species. This particular trait has evolved independently several times in each of the four families of amphidromous fish that have given rise to significant freshwater radiations. Amongst the New Zealand galaxiids, mean egg diameter increased with maximum body length for both non‐migratory and amphidromous species; however, despite the considerably smaller relative body size of the non‐diadromous species, the rate of increase in egg diameter relative to the increase in body size is considerably higher in the non‐migratory fish. We propose that amphidromous fish maintain a high level of fecundity by producing small pelagic larvae. In contrast, the relatively large eggs and well‐developed larvae of non‐migratory species increase larval survival in what are often relatively harsh and unproductive freshwater habitats. Consequently, amphidromous species are likely to have a competitive advantage over their non‐migratory relatives when close to a pelagic habitat in which their larvae can grow and develop and then migrate upstream, releasing them from recruitment limitation and giving them a local reproductive advantage over their less fecund non‐migratory relatives. We argue that the persistence and distribution of both life‐history strategies across the landscape depends on the relative difference in the net reproductive return for each strategy in relation to distance from a pelagic larval habitat, as mediated by the relative costs of migration and egg size/fecundity relationships.

In times of biodiversity crisis there is an increasing need for faster and cheaper methods by which to achieve conservation goals. This situation is especially troublesome for invertebrates, and the use of morphospecies instead of taxonomic species has been proposed as a way around the taxonomic constraints in particular situations. We conducted a study in a modified native shrubland on New Zealand's South Island in which we sampled Lepidoptera, Coleoptera, and Araneae in autumn by beating and pitfall traps. All specimens were separated into morphospecies by a nonspecialist and identified by specialized taxonomists, and the results were compared. Results were analyzed with respect to correct separations (one taxonomic species to one morphospecies), lumping (more than one species classified as a single morphospecies), and splitting (one species separated into more than one morphospecies). Among the individual orders, Lepidoptera yielded the most accurate results (91% correct separation), whereas Coleoptera and Araneae yielded poor results (63% and 50%, respectively). The overall difference between the morphospecies and taxonomic species estimates for the site was only 3.3%, but this was an artifact caused by the splitting and lumping results balancing each other out. The accuracy of morphospecies separation varies greatly among different invertebrate groups, so the relationship between morphospecies and taxonomic species for a particular target group must be established beforehand. We recommend that some prior orientation should be given by expert taxonomists. When adopted with care, morphospecies present a useful tool for conservation, particularly for environmental impact assessment and when inventorying diversity does not require information on particular species.

Summary 1. Seasonal variation in microhabitat use and activity of 14 giant kokopu Galaxias argenteus, a drift‐feeding galaxiid fish, was compared using radiotelemetry. 2. During winter giant kokopu predominantly used low velocities and intermediate depths by night and day. Activity recorded during 24 and 72 h periods indicated that fish were consistently active at night and inactive during the day. Activity data corresponded with point‐in‐time habitat use data, both of which indicated that fish were concealed amongst cover during the day and used open water habitats at night. 3. During summer, giant kokopu used higher water velocities, shallower depths and coarser substrata, particularly at night but also occasionally during the day relative to winter. Giant kokopu were active by both day and night in summer, although periods of activity were less defined and less predictable than during winter. 4. Adults used predictable home reaches at base‐flow, with most individuals repeatedly using of one or two cover locations within their ‘home’ reach. Reaches used by fish were relatively short (rarely exceeding 26 m) irrespective of season and always included a single pool‐riffle sequence. 5. Diel and seasonal behaviour of giant kokopu was generally comparable with that exhibited by other drift feeding fish species in small temperate streams. However, the nocturnal activity of giant kokopu contrasts with activity patterns in various salmonids, indicating that the impact of predation by different drift feeding fish may vary considerably.

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