Scale‐dependent genetic structure of the Idaho giant salamander (Dicamptodon aterrimus) in stream networks

The network architecture of streams and rivers constrains evolutionary, demographic and ecological processes of freshwater organisms. This consistent architecture also makes stream networks useful for testing general models of population genetic structure and the scaling of gene flow. We examined genetic structure and gene flow in the facultatively paedomorphic Idaho giant salamander, Dicamptodon aterrimus, in stream networks of Idaho and Montana, USA. We used microsatellite data to test population structure models by (i) examining hierarchical partitioning of genetic variation in stream networks; and (ii) testing for genetic isolation by distance along stream corridors vs. overland pathways. Replicated sampling of streams within catchments within three river basins revealed that hierarchical scale had strong effects on genetic structure and gene flow. amova identified significant structure at all hierarchical scales (among streams, among catchments, among basins), but divergence among catchments had the greatest structural influence. Isolation by distance was detected within catchments, and in‐stream distance was a strong predictor of genetic divergence. Patterns of genetic divergence suggest that differentiation among streams within catchments was driven by limited migration, consistent with a stream hierarchy model of population structure. However, there was no evidence of migration among catchments within basins, or among basins, indicating that gene flow only counters the effects of genetic drift at smaller scales (within rather than among catchments). These results show the strong influence of stream networks on population structure and genetic divergence of a salamander, with contrasting effects at different hierarchical scales.     

Colonization of an artificial stream by fishes and aquatic macro-invertebrates

We examined colonization by fishes and macro-invertebrates from permanent streams into an artificial freshwater stream simulating lotic temporary bodies of water that exist for only a limited period each year. After introducing water, invertebrates such as chironomid larvae in mud increased in numbers rapidly in the experimental stream, although they were rare in mud in the permanent streams. Eleven of 12 fish species present in the permanent streams colonized the experimental stream and preyed upon invertebrates, although fish composition differed significantly between the two streams. About 100 days after the initiation of the experiment, both species richness and diversity in the experimental stream reached almost the same level as that in the permanent streams. More diverse fishes colonized the complex section where habitat diversity was high compared to the simple section in the experimental stream. Our study strongly suggests that lotic temporary waters such as temporary streams around main rivers have unique ecological characteristics and serve as valuable foraging sites for fish.     

Testing the River Continuum Concept with geostatistical stream-network models

The River Continuum Concept (RCC) provided one of the first unifying frameworks in fluvial ecosystem theory. While the RCC predictions held in many empirical tests, other research highlighted how the model overlooked sources of heterogeneity at different scales e.g. the effects of tributaries. Disentangling these effects requires an assessment of variation in key ecosystem variables over the longitudinal and lateral dimension of river networks. However, so far, no empirical tests have employed a spatially explicit statistical approach to this assessment.Here, we show how recently-developed spatially-explicit models for river networks can be used to test predictions of the RCC whilst taking into account cross-scale sources of heterogeneity. We used macroinvertebrate data from 195 monitoring sites from 1^st to 4^th order streams spread across the Adige River network (NE Italy). We compared theoretical expectations with empirical semivariograms that incorporated network topology to assess the continuity and patchiness in the proportion of invertebrates functional feeding groups (FFG) over Euclidean and in-stream distances. Geostatistical stream-network models were then used to quantify the influence of the longitudinal gradient relative to local-scale water quality and land-use drivers, while accounting for network spatial autocorrelation.Patterns in the semivariograms based on flow-connected relationships were characterised by a nested structure associated with heterogeneity at multiple scales. Therefore, the longitudinal variation in FFG was better described by a patchy discontinuum rather than a gradient, implying that both in-stream processes and landscape factors influenced stream ecosystem function. The overall shift in FFG along the longitudinal profile was generally consistent with the RCC predictions, although the best models often included water quality and local land-use predictors. Stream-network models further indicated that up to 90% of residual variation (mean=50%) was accounted for by spatial autocorrelation, especially among flow-connected communities. Accounting for such autocorrelation not only improved model performance relative to non-spatial approaches, but indicated that most flow-connected communities were spatially correlated to some extent. This has clear implications for the assessment of the RCC tenets. This is the first test of the river continuum model that explicitly accounted for stream network topology and autocorrelation. Results indicated that in the Adige River, macroinvertebrates feeding groups exhibited heterogeneity along the longitudinal gradient, which appeared punctuated by local habitat transitions. Such transitions could be associated with artificial impoundments that alter the natural continuity of river processes, and we advocate the use of spatially explicit network models to test the RCC in more natural contexts.     

Geomorphology and fish assemblages in a Piedmont river basin, U.S.A.

1. We investigated linkages between fishes and fluvial geomorphology in 31 wadeable streams in the Etowah River basin in northern Georgia, U.S.A. Streams were stratified into three catchment sizes of approximately 15, 50 and 100 km², and fishes and geomorphology were sampled at the reach scale (i.e. 20–40 times stream width). 2. Non‐metric multidimensional scaling (NMDS) identified 85% of the among‐site variation in fish assemblage structure and identified strong patterns in species composition across sites. Assemblages shifted from domination by centrarchids, and other pool species that spawn in fine sediments and have generalised food preferences, to darter‐cyprinid‐redhorse sucker complexes that inhabit riffles and runs, feed primarily on invertebrates, and spawn on coarser stream beds. 3. Richness and density were correlated with basin area, a measure of stream size, but species composition was best predicted (i.e. |r| between 0.60–0.82) by reach‐level geomorphic variables (stream slope, bed texture, bed mobility and tractive force) that were unrelated to stream size. Stream slope was the dominant factor controlling stream habitat. Low slope streams had smaller bed particles, more fines in riffles, lower tractive force and greater bed mobility compared with high slope streams. 4. Our results contrast with the ‘River Continuum Concept’ which argues that stream assemblages vary predictably along stream size gradients. Our findings support the ‘Process Domains Concept’, which argues that local‐scale geomorphic processes determine the stream habitat and disturbance regimes that influence stream communities.     

Functional diversity and trait–environment relationships of stream fish assemblages in a large tropical catchment

1. The species composition of stream fish assemblages changes across the longitudinal fluvial gradient of large river basins. These changes may reflect both zonation in species distributions and environmental filtering of fish traits as stream environments change from the uplands to the lowlands of large catchments. Previous research has shown that taxonomic diversity generally increases in larger, lowland streams, and the River Continuum Concept, the River Habitat Template and other frameworks have provided expectations for what functional groups of fishes should predominate in certain stream types. However, studies addressing the functional trait composition of fish assemblages across large regions are lacking, particularly in tropical river basins. 2. We examined functional trait–environment relationships and functional diversity of stream fish assemblages in the Río Grijalva Basin in southern Mexico. Traits linked to feeding, locomotion and life history strategy were measured in fishes from streams throughout the catchment, from highland headwaters to broad, lowland streams. Relationships between functional traits and environmental variables at local and landscape scales were examined using multivariate ordination, and the convex hull volume of trait space occupied by fish assemblages was calculated as a measure of functional diversity. 3. Although there were a few exceptions, functional diversity of assemblages increased with species richness along the gradient from uplands to lowlands within the Grijalva Basin. Traits related to swimming, habitat preference and food resource use were associated with both local (e.g. substratum type, pool availability) and landscape‐scale (e.g. forest cover) environmental variables. 4. Along with taxonomic structure and diversity, the functional composition of fish assemblages changed across the longitudinal fluvial gradient of the basin. Trait–environment relationships documented in this study partially confirmed theoretical expectations and revealed patterns that may help in developing a better understanding of general functional responses of fish assemblages to environmental change.     

Concordance among stream assemblages and spatial autocorrelation along a fragmented gradient

Patterns of spatial autocorrelation of biota and distributional similarity (concordance) between assemblages of different organism groups have important implications in both theoretical ecology and biodiversity conservation. Here we report environmental gradients and spatial distribution patterns of taxonomic composition among stream fish, benthic macroinvertebrate, and diatom assemblages along a fragmented stream in south‐western France. We quantified spatial patterns of lotic assemblage structure along this stream, and we tested for concordance in distribution patterns among the three taxonomic groups. Our results showed that both environmental characteristics and stream assemblages were spatially autocorrelated. For stream fish and diatom assemblages, these patterns reflected assemblage changes along the longitudinal stream gradient, whereas environmental variables and benthic macroinvertebrates exhibited a more patchy spatial pattern. Cross‐taxa concordance was significant between stream fish and diatoms, and between stream fish and benthic macroinvertebrates. The assemblage concordance between stream fish and diatoms could be attributed to similar responses along the longitudinal gradient, whereas those between stream fish and benthic macroinvertebrates may result from biotic interactions. Based on potential dispersal capacities of taxa, our results validated the hypotheses that weakly dispersing taxa exhibit greater concordance than highly dispersing ones and that dispersal capacities affect how taxonomic groups respond to their local environment. Both diatoms and highly dispersing stream fish were affected by stream fragmentation (i.e. the number of dams between sites), while the effect of fragmentation was not significant for invertebrates that fly well in their adult stage, thus emphasizing the importance of the way of dispersal. These results suggest that addressing the effects of dispersal capacity on stream assemblage patterns is crucial to identifying mechanisms behind patterns and to better understanding the determinants of stream biodiversity.     

Biodiversity: towards a unifying theme for river ecology

1. A broadened concept of biodiversity, encompassing spatio‐temporal heterogeneity, functional processes and species diversity, could provide a unifying theme for river ecology. 2. The theoretical foundations of stream ecology often do not reflect fully the crucial roles of spatial complexity and fluvial dynamics in natural river ecosystems, which has hindered conceptual advances and the effectiveness of efforts at conservation and restoration. 3. Inclusion of surface waters (lotic and lentic), subsurface waters (hyporheic and phreatic), riparian systems (in both constrained and floodplain reaches), and the ecotones between them (e.g. springs) as interacting components contributing to total biodiversity, is crucial for developing a holistic framework of rivers as ecosystems. 4. Measures of species diversity, including alpha, beta and gamma diversity, are a result of disturbance history, resource partitioning, habitat fragmentation and successional phenomena across the riverine landscape. A hierarchical approach to diversity in natural and altered river‐floodplain ecosystems will enhance understanding of ecological phenomena operating at different scales along multidimensional environmental gradients. 5. Re‐establishing functional diversity (e.g. hydrologic and successional processes) across the active corridor could serve as the focus of river conservation initiatives. Once functional processes have been reconstituted, habitat heterogeneity will increase, followed by corresponding increases in species diversity of aquatic and riparian biota.     

The lentic and lotic characteristics of habitats determine the distribution of benthic macroinvertebrates in Mediterranean rivers

1. The importance of flow‐related factors to benthic organisms, as well as the role of habitat conditions in shaping aquatic communities during low‐flow periods, have been recognised. Despite this, the preferences of macroinvertebrates to the ratio of lentic to lotic habitats at the reach scale have not been accurately quantified in most instances.
2. Aquatic invertebrates and habitat features in a range of temporary rivers in Sardinia were investigated. The investigation focused on the flow‐related characteristics that contribute to defining the lentic–lotic condition of the river reaches. The relation of habitat features to benthic taxa distributions was assessed using multidimensional scaling. The main aim of the paper was to quantify the responses of taxa to the different lentic and lotic habitat conditions by applying hierarchical logistic regressions. Finally, taxon optima were aligned along the lentic–lotic gradient and the responses of different taxonomic groups compared.
3. Unbroken waves and imperceptible flow were correlated with benthic taxa variability, suggesting local hydraulics and turbulence have a major role in regulating community composition. The overall lentic–lotic character of the river reaches was also clearly related to the benthic taxa distribution. More than 80% of taxa were significantly related to the lentic–lotic gradient, and an asymmetrical response curve was the predominant model.
4. Benthic groups showed taxon optima clustered in different ranges of the lentic–lotic gradient. Odonata, Coleoptera, Hemiptera, and Mollusca preferred clearly lentic conditions. Diptera mainly ranged on the lotic side of the gradient, while Trichoptera were relatively uniformly distributed across the gradient. Ephemeroptera taxa clustered in intermediate lentic–lotic conditions, with two species preferring extremely lentic habitats. In general, optima converged at intermediate and extremely lentic conditions, presumably due, respectively, to the coexistence of different lentic and lotic features and to the highly diverse environmental characteristics under extremely lentic situations.
5. These results support the conclusion that dissimilar ecological factors act on benthic taxa along the lentic–lotic range and species favouring different lentic–lotic conditions are subjected to pressures of different nature. This should not be ignored when defining species preferences and studying community structure or relationships between species in Mediterranean rivers, which cyclically vary their habitat composition. In addition, the uneven distribution of optima of different groups along the lentic–lotic gradient might affect macroinvertebrate metrics when assessing ecological status or establishing reference conditions under variable climatic conditions.

     

Virus ecology of fluvial systems: a blank spot on the map?

The ecology of viruses has been studied only in a limited number of rivers and streams. In light of a recent re‐appraisal of the global fluvial surface area, issues such as abundance and production, host mortality and the influence of suspended particles and biofilms are addressed. Viral life cycles, potential impacts of viruses on water biochemistry and carbon flow, and viral diversity are considered. Variability in trophic levels along with the heterogeneous nature and hydrological dynamics of fluvial environments suggest a prevailingly physical control of virus‐related processes under lotic conditions and more biological control under lentic conditions. Viral lysis likely contributes to a pool of rapidly cycling carbon in environments typically characterized by high proportions of recalcitrant terrestrial carbon. On average, 33.6% (equalling 0.605 Pg C year^?1) of the globally respired carbon from fluvial systems may pass through a viral loop. Virus distribution and the proportion of organic material in horizontal transport versus processes in retention zones remain to be determined in detail. The need for up‐scaling the contribution of virus‐related processes in fluvial systems is of global relevance. Further, the role of climate change and the effect of anthropogenic alterations of fluvial systems on viruses require attention. The identification of these considerable knowledge gaps should foster future research efforts.     

Parallels and contrasts between intermittently freezing and drying streams: From individual adaptations to biodiversity variation

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Variability and convergence in benthic communities along the longitudinal gradients of four physically similar Rocky Mountain streams

1. High‐gradient mountain streams are ideal for studying longitudinal biological patterns, although the degree of similarity in the biological gradient among physically similar streams in a region is poorly known. Our first objective was to evaluate variability in benthic communities along four streams in the central Rocky Mountains of Colorado. We analysed the relative influence of longitudinal position versus reach‐scale physical variables on community structure and measured community similarity at comparable longitudinal positions on the four streams. 2. Our second objective was to evaluate the relative utility of taxonomically versus functionally defined communities to characterise assemblage structure: are taxonomic patterns more predictable along the gradient than are patterns of ecologically important species traits? 3. Redundancy analyses (RDA), including measures of both reach‐scale environmental variables (substratum properties, periphytic cover, local channel slope) and longitudinal position (altitude, stream size), confirmed that the longitudinal position of a site was most important in determining taxonomic composition. Functional community structure was also influenced by longitudinal position, but reach‐scale variables (especially periphyton and median particle size) were of greater importance. 4. Redundancy analyses explained 29.3% of total taxonomic variance and 26.0% of functional variance, indicating that defining assemblages functionally provides no greater understanding of community patterns given several known environmental variables. Strict longitudinal limits of taxa, the presumably identical regional species pool across our sites, and/or trade‐offs among different types of species traits probably explain this result. 5. Redundancy analyses did suggest, however, that traits related to longer life (semivoltinism, long‐lived adults, and slow larval development) were more common downstream, while long‐distance dispersal ability and high fecundity were associated with higher altitude and its associated harsher conditions. 6. When sampling sites were grouped into three ecological zones defined by altitude, mean community similarity (measured both taxonomically and functionally) was lowest across streams at the highest altitude. This pattern could be driven by increased insularity of alpine‐zone streams, resulting from a combination of harsh terrestrial environment, lack of hydrological connectivity, and limited species ranges along the longitudinal continuum.     

Importance of low-flow and high-flow characteristics to restoration of riparian vegetation along rivers in arid south-western United States

1. Riparian vegetation in dry regions is influenced by low‐flow and high‐flow components of the surface and groundwater flow regimes. The duration of no‐flow periods in the surface stream controls vegetation structure along the low‐flow channel, while depth, magnitude and rate of groundwater decline influence phreatophytic vegetation in the floodplain. Flood flows influence vegetation along channels and floodplains by increasing water availability and by creating ecosystem disturbance. 2. On reference rivers in Arizona's Sonoran Desert region, the combination of perennial stream flows, shallow groundwater in the riparian (stream) aquifer, and frequent flooding results in high plant species diversity and landscape heterogeneity and an abundance of pioneer wetland plant species in the floodplain. Vegetation changes on hydrologically altered river reaches are varied, given the great extent of flow regime changes ranging from stream and aquifer dewatering on reaches affected by stream diversion and groundwater pumping to altered timing, frequency, and magnitude of flood flows on reaches downstream of flow‐regulating dams. 3. As stream flows become more intermittent, diversity and cover of herbaceous species along the low‐flow channel decline. As groundwater deepens, diversity of riparian plant species (particularly perennial species) and landscape patches are reduced and species composition in the floodplain shifts from wetland pioneer trees (Populus, Salix) to more drought‐tolerant shrub species including Tamarix (introduced) and Bebbia. 4. On impounded rivers, changes in flood timing can simplify landscape patch structure and shift species composition from mixed forests composed of Populus and Salix, which have narrow regeneration windows, to the more reproductively opportunistic Tamarix. If flows are not diverted, suppression of flooding can result in increased density of riparian vegetation, leading in some cases to very high abundance of Tamarix patches. Coarsening of sediments in river reaches below dams, associated with sediment retention in reservoirs, contributes to reduced cover and richness of herbaceous vegetation by reducing water and nutrient‐holding capacity of soils. 5. These changes have implications for river restoration. They suggest that patch diversity, riparian plant species diversity, and abundance of flood‐dependent wetland tree species such as Populus and Salix can be increased by restoring fluvial dynamics on flood‐suppressed rivers and by increasing water availability in rivers subject to water diversion or withdrawal. On impounded rivers, restoration of plant species diversity also may hinge on restoration of sediment transport. 6. Determining the causes of vegetation change is critical for determining riparian restoration strategies. Of the many riparian restoration efforts underway in south‐western United States, some focus on re‐establishing hydrogeomorphic processes by restoring appropriate flows of surface water, groundwater and sediment, while many others focus on manipulating vegetation structure by planting trees (e.g. Populus) or removing trees (e.g. Tamarix). The latter approaches, in and of themselves, may not yield desired restoration outcomes if the tree species are indicators, rather than prime causes, of underlying changes in the physical environment.     

Ecotones and fluvial regimes in arctic lotic environments

The fluvial regime in arctic streams is influenced by size of stream, the presence and storage capacity of lakes in the drainage basin, groundwater, and permafrost. Exchange of material with terrestrial environments depends on the season and is more or less suspended in winter. Permafrost and water storage in ice and snow control run off and erosion. Damage to vegetation by flooding, fire, animal or human activity can affect the permafrost and result in rapid erosion. Living space and conditions in lotic environments are modified by ice and during break up are very labile. Fish and benthic organisms in streams have behavioural and physiological adaptations which allow them to benefit from the wide range of river and stream environments found in the arctic and to tolerate the range of seasonal conditions. Ecotones are weakly developed in arctic streams and are of minor functional significance. Only farther south does riparian vegetation begin to play a role in regulating stream processes and not until south of the tree line can ecotones be considered important modulators of fluvial environments.     

Genetic population structure of the net-winged midge, Elporia barnardi (Diptera: Blephariceridae) in streams of the south-western Cape, South Africa: implications for dispersal

SUMMARY 1. The net‐winged midges (Diptera: Blephariceridae), with highly specific habitat requirements and specialised morphological adaptations, exhibit high habitat fidelity and a limited potential for dispersal. Given the longitudinal and hierarchical nature of lotic systems, along with the geological structure of catchment units, we hypothesise that populations of net‐winged midge should exhibit a high degree of population sub‐structuring. 2. Sequence variation in the cytochrome c oxidase subunit I (COI) region of the mitochondrial DNA (mtDNA) was examined to determine patterns of genetic variation and infer historical and contemporary processes important in the genetic structuring of populations of Elporia barnardi. The DNA variation was examined at sites within streams, between streams in the same range, and between mountain ranges in the south‐western Cape of South Africa. 3. Twenty‐five haplotypes, 641 bp in length, were identified from the 93 individuals sampled. A neighbour‐joining tree revealed two highly divergent clades (～5%) corresponding to populations from the two mountain ranges. A number of monophyletic groups were identified within each clade, associated with individual catchment units. 4. The distribution of genetic variation was examined using analysis of molecular variance (amova ). This showed most of the variation to be distributed among the two ranges (～80%), with a small percentage (～15%) distributed among streams within each range. Similarly, variation among streams on Table Mountain was primarily distributed among catchment units (86%). A Mantel's test revealed a significant relationship between genetic differentiation and geographical distance, suggesting isolation by distance (P < 0.001). 5. Levels of sequence divergence between the two major clades, representing the two mountain ranges, are comparable with those of some intra‐generic species comparisons. Vicariant events, such as the isolation of the Peninsula mountain chain and Table Mountain, may have been important in the evolution of what is now a highly endemic fauna. 6. The monophyletic nature of the catchment units suggests that dispersal is confined to the stream environment and that mountain ridges provide effective physical barriers to dispersal of E. barnardi.     

Benthic macroinvertebrate assemblages of coastal and continental streams and large rivers of southwestern British Columbia, Canada

In southwestern British Columbia (BC, Canada) and within a relatively small geographic area, lotic environments range from streams in coastal rainforests, to streams in arid continental grasslands, to very large rivers. Little is known about the invertebrate communities in large rivers in general, or in the streams of continental BC. The purpose of this study was to determine whether the benthic invertebrate community structure changes spatially between small coastal and small interior streams; between small streams versus large rivers; and whether changes in the benthic community are related to the environmental conditions. Kicknet samples and environmental data were collected from three coastal streams, three continental streams and two large rivers (discharge of 781 and 3620 m³/s, respectively). The large river sites had low invertebrate abundance, species richness and diversity, relative to the small streams. The coastal streams had the highest species richness and the continental streams had the highest invertebrate abundance. A number of taxa were specific to each class of stream. Invertebrate abundance decreased with river size, and increased with elevation, pH, conductivity, alkalinity, NO₂NO₃-N, total Kejldahl nitrogen and percent carbon in suspended solids.     

Headwaters are critical reservoirs of microbial diversity for fluvial networks

Streams and rivers form conspicuous networks on the Earth and are among nature''s most effective integrators. Their dendritic structure reaches into the terrestrial landscape and accumulates water and sediment en route from abundant headwater streams to a single river mouth. The prevailing view over the last decades has been that biological diversity also accumulates downstream. Here, we show that this pattern does not hold for fluvial biofilms, which are the dominant mode of microbial life in streams and rivers and which fulfil critical ecosystem functions therein. Using 454 pyrosequencing on benthic biofilms from 114 streams, we found that microbial diversity decreased from headwaters downstream and especially at confluences. We suggest that the local environment and biotic interactions may modify the influence of metacommunity connectivity on local biofilm biodiversity throughout the network. In addition, there was a high degree of variability in species composition among headwater streams that could not be explained by geographical distance between catchments. This suggests that the dendritic nature of fluvial networks constrains the distributional patterns of microbial diversity similar to that of animals. Our observations highlight the contributions that headwaters make in the maintenance of microbial biodiversity in fluvial networks.     

A New Field Procedure and Method of Analysis to Evaluate the Performance of Bacillus thuringiensis subsp. israelensis Liquid Formulations in Streams and Rivers

Many field tests have shown Bacillus thuringiensis subsp. israelensis ( Bti ) to be an effective simuliid larvicide. However, literature indicates that an effective evaluation and comparison of Bti -based formulations when tested in streams or rivers is difficult. Most field trials have been conducted in different rivers (different discharge, river profile, water temperature, suspended matter, larval species, etc.), thus rendering the evaluation of the performance of liquid formulations of Bti very arbitrary or even impossible. A new field procedure is proposed to evaluate the performance of liquid formulations of Bti in the same lotic environment and under similar abiotic and biotic conditions. The procedure, based on a system of gutters located on the bank of a stream, showed very good reproducibility of the mortality levels of the target pest(s) recorded at various distances (stations) along the stream over a two-year field trial, proving the efficacy of the system. The system allows either a single formulation or different formulations to be tested repeatedly in the same portion of a stream, thereby providing a more accurate evaluation of the performance of a Bti formulation or a much better comparison between different formulations. The use of the probit model (allowing comparison of slopes and intercepts) gives a reliable statistical value for the analysis of the results. Moreover, this system is not expensive and can be transferred easily to other streams or rivers.     

Using multivariate adaptive regression splines to predict the distributions of New Zealand's freshwater diadromous fish

1. Relationships between probabilities of occurrence for fifteen diadromous fish species and environmental variables characterising their habitat in fluvial waters were explored using an extensive collection of distributional data from New Zealand rivers and streams. Environmental predictors were chosen for their likely functional relevance, and included variables describing conditions in the stream segment where sampling occurred, downstream factors affecting the ability of fish to move upriver from the sea, and upstream, catchment‐scale factors mostly affecting variation in river flows. 2. Analyses were performed using multivariate adaptive regression splines (MARS), a technique that uses piece‐wise linear segments to describe non‐linear relationships between species and environmental variables. All species were analysed using an option that allows simultaneous analysis of community data to identify the combination of environmental variables best able to predict the occurrence of the component species. Model discrimination was assessed for each species using the area under the receiver operating characteristic curve (ROC) statistic, calculated using a bootstrap procedure that estimates performance when predictions are made to independent data. 3. Environmental predictors having the strongest overall relationships with probabilities of occurrence included distance from the sea, stream size, summer temperature, and catchment‐scale drivers of variation in stream flow. Many species were also sensitive to variation in either the average and/or maximum downstream slope, and riparian shade was an important predictor for some species. 4. Analysis results were imported into a Geographic Information System where they were combined with extensive environmental data, allowing spatially explicit predictions of probabilities of occurrence by species to be made for New Zealand's entire river network. This information will provide a valuable context for future conservation management in New Zealand's rivers and streams.     

Reconstructing riverine mesohabitat unit composition using fish community data and an autecology matrix

This research proposes a simplified method for estimating the mesohabitat composition that would favour members of a given set of aquatic species. The simulated composition of four types of mesohabitat units (deep pool, shallow pool, deep riffle and shallow riffle) could guide the design of in‐stream structures in creating pool‐riffle systems with ecological reference. Fish community data and an autecology matrix are used to support the development of a stream mesohabitat simulation based on regression models for reaches in mid to upper‐order streams. The fish community‐mesohabitat model results constitute a reference condition that can be used to guide stream restoration and ecological engineering decisions aimed at maintaining the natural ecological integrity and diversity of rivers.     

Development of a macroinvertebrate multimetric index for the assessment of low-land streams in the neotropics

The water and habitat quality in Panamanian streams and rivers are being degraded by agriculture, urbanization, industrial activities, mining, and other forms of development. Thus, the need for standards, especially those examining the biological attributes of lotic systems, are urgently required. We describe the development of a multimetric index based on macroinvertebrates collected in low-land streams in the Panama Canal Watershed (PCW), which differed in their levels of human impacts. The index was developed using 12 streams and validated using a further three, all of which were sampled on four occasions, in the dry and wet seasons of 2007 and 2008. We examined 42 metrics related to macroinvertebrate community structure, composition, and function. Based on their ability to distinguish reference from moderately or severely impacted streams, and on their independence, we selected seven metrics (Margalef's index (taxa), Shannon's evenness index (taxa), number of EPT (taxa), % of Trichoptera, ratio of Chironomidae/Diptera individuals, % of scrapers, and % of shredders). These metrics were then standardized and developed into the Neotropical Low-land Stream Multimetric Index (NLSMI). Overall, the NLSMI distinguished well among the different levels of impairment (Reference, Moderate impact, and Severe impact) and showed a strong, significant correlation with principal component analysis (PCA) axis one values, with the PCA based on a set of physico-chemical variables indicative of stream quality. The wet season generally resulted in lower NLSMI values, leading us to suggest that sampling for biomonitoring be carried out in the dry season. Overall, this preliminary macroinvertebrate NLSMI shows promise for developing a biomonitoring programme to assess the ecological integrity of streams, to aid with management, restoration, and conservation, and to serve as a basis to develop a more geographically extensive multimetric index.