Using diatoms to assess human impacts on streams benefits from multiple-habitat sampling

Benthic diatoms are important indicators of human impacts on streams. Epilithic diatoms are collected most often for bioassessments, but potentially important ecological information from other habitats could be missed. Within our study region, substrata ranged from 100% rock to 100% sandy silt at 61 sites, leading us to question the appropriateness of sampling solely epilithic surfaces in riffles. We compared two protocols for collecting diatoms: (1) epilithic habitat samples (EHS) within riffles and (2) multi-habitat samples (MHS), which proportionately included different habitats (e.g., riffles and pools) and substrata (e.g., sand, silt, and rock). Three streams were not compared because rocks were absent. Nonmetric multidimensional scaling indicated that diatom communities from EHS and MHS responded similarly to alkalinity and agricultural gradients, and Procrustes analysis showed that ordinations were similar (P < 0.01). Percent motile diatoms and metrics indicating high or low P and N from MHS showed stronger relationships with land use variables than those metrics from EHS. Bray-Curtis (BC) similarity between the protocols increased as diversity and richness decreased in MHS, as agricultural impacts increased, and as motile diatoms became more abundant in EHS, which likely indicated greater habitat homogeneity or an overriding effect of water chemistry. The two protocols classified 78% of sites concordantly as minimally impacted or impacted. Multi-habitat sampling is preferred where stream habitats vary greatly because it assessed land use impacts more effectively than EHS, while indicating water chemistry impacts as effectively. Multiple habitats also contained greater species diversity, which is important to documenting species distributions, and were always available for sampling, whereas epilithic habitats could be sparse or absent.     

Habitat diversity and species diversity: testing the competition hypothesis with juvenile salmonids

I experimentally tested two predictions of the hypothesis that the positive relationship between habitat diversity and species diversity arises from a reduction in the negative effects of interspecific competition. By allowing species to partition habitat and avoid competition, habitat diversity should 1) facilitate the addition of an ecologically intermediate species into an existing community, and 2) reduce the negative effects of that species on existing members of the community. I tested these predictions with juveniles of three sympatric salmonid species: coho salmon ( Oncorhynchus kisutch ), steelhead trout ( O. mykiss ), and cutthroat trout ( O. clarki ), which in natural streams occupy deep low-velocity pools, shallow high-velocity riffles, and intermediate habitats, respectively. I introduced two (coho and steelhead) and three species communities into each of three artificial stream habitats: pools, riffles, and diverse. The results provide partial support for the predictions. Cutthroat trout grew fastest in the diverse stream habitat. Though habitat diversity did not eliminate the negative effects of competition, in the three species community coho and steelhead grew as fast in the diverse habitat as in either homogeneous habitat. The results are consistent with data on species number and evenness from natural communities, where variation along other niche axes confounds the relationship between habitat diversity, interspecific competition, and species diversity.     

Diatoms as indicators of river quality in the Nepalese Middle Hills with consideration of the effects of habitat-specific sampling

1. Using a replicated survey design at the catchment scale, we compared the composition and diversity of diatom communities in three stream groups in the Middle Hills of Nepal: semi-natural reference (Arun Valley), enriched by agricultural runoff (Likhu Khola) and grossly polluted by sewage (Kathmandu Valley). We sampled riffles at all sites; in the Kathmandu Valley and Likhu Khola we also sampled diatoms in pools and on vegetation.
2. Species richness and diversity H' were significantly higher in agricultural streams than in either organically polluted streams or references. Community composition, as shown by principal components analysis, varied significantly between all three stream types due to differences in the abundances of species characteristic of organic enrichment (Kathmandu Valley), moderate enrichment (Likhu Khola) or undisturbed hillstreams (Arun Valley).
3. Few species varied in relative abundance between pools, riffles and vegetation so that variations in community composition and diversity were stronger between stream groups than between habitats. Samples from any one habitat produced only 75.7% (± 8.6 SD) of the species from three habitats, so that surveys aimed at recording biodiversity may need more comprehensive habitat coverage than surveys for biomonitoring.
4. We conclude that diatom communities can indicate different sources of pollution in Nepalese streams, and advocate further studies to develop this indicator potential over a wider area of the Himalaya. Comparisons between replicate groups of streams selected a priori helped to clarify effects which were sometimes obscured by other survey designs.     

Diatoms as indicators of river quality in the Nepalese Middle Hills with consideration of the effects of habitat-specific sampling

1. Using a replicated survey design at the catchment scale, we compared the composition and diversity of diatom communities in three stream groups in the Middle Hills of Nepal: semi-natural reference (Arun Valley), enriched by agricultural runoff (Likhu Khola) and grossly polluted by sewage (Kathmandu Valley). We sampled riffles at all sites; in the Kathmandu Valley and Likhu Khola we also sampled diatoms in pools and on vegetation.
2. Species richness and diversity H' were significantly higher in agricultural streams than in either organically polluted streams or references. Community composition, as shown by principal components analysis, varied significantly between all three stream types due to differences in the abundances of species characteristic of organic enrichment (Kathmandu Valley), moderate enrichment (Likhu Khola) or undisturbed hillstreams (Arun Valley).
3. Few species varied in relative abundance between pools, riffles and vegetation so that variations in community composition and diversity were stronger between stream groups than between habitats. Samples from any one habitat produced only 75.7% (± 8.6 SD) of the species from three habitats, so that surveys aimed at recording biodiversity may need more comprehensive habitat coverage than surveys for biomonitoring.
4. We conclude that diatom communities can indicate different sources of pollution in Nepalese streams, and advocate further studies to develop this indicator potential over a wider area of the Himalaya. Comparisons between replicate groups of streams selected a priori helped to clarify effects which were sometimes obscured by other survey designs.     

Case studies on decapod crustaceans from the Philippines reveal deep,steep underwater slopes as prime habitats for ‘rare’ species

Relatively few studies have been done to define or assess rarity in the marine environment. Published studies have focused on shallow-water and intertidal habitats, and the available information appears to reflect the same pattern observed in terrestrial environments, i.e., that there are many rare species and few common species in any one given area. However, our studies of the abundance of new and/or supposedly rare taxa of decapod crustaceans from the deep, steep slopes of the island of Balicasag, in the central Philippines, have raised questions on how rarity should be defined in marine invertebrates. Examples of such supposedly rare species of crabs and lobsters (Crustacea: Decapoda) are presented here. That these animals come from deep, steep slopes, a relatively under-studied habitat, highlights the major gaps in current knowledge of marine biodiversity that are in part due to the inadequacy of both traditional and high technology sampling methodologies and the limited habitat types that the former can target. Low-technology, artisanal tangle nets have proved to be an optimal capture technique for deep-water decapod crustaceans on deep, steep slopes; many new taxa have been discovered and, in other cases, perceptions of rarity and endemicity have been corrected.     

Habitat structure and invertebrate assemblages on stream stones: A multivariate view from the riffle

Abstract Highly structured habitats, those with complex or heterogeneous physical structure, commonly contain more species than simply structured ones. However, tests of this relationship have been hampered by habitat-specific definitions and measurements of habitat structure and, in stream studies, by insufficient information on spatial variation in faunal abundances. We sampled the fauna of 90 stones collected from an order 4 section of the Taggerty and Steavenson Rivers, southeastern Australia. The spatially nested sampling design encompassed three spatial scales (sites within the same stream order, riffles at the same site and groups of stones within the same riffle) but no temporal replication, as we were only able to sample once. Habitat structure of stones was quantified by measuring the amount and type of epilithon on stones, together with stone shapes, sizes, textures and surface complexities. For the latter two attributes, we used a new method, involving image analysis, which can be used to quantify habitat structure in comparable ways in other systems. Species richness (S) was related to some measures of habitat structure, being higher on stones with a rough texture and weakly related to the amount of epilithon present. Total numbers of individuals (N) were also higher on rough stones, and faunal composition (as quantified by hybrid multidimensional scaling) was related to abundance of epilithon. However, flow environments, as quantified by water velocities and depths, were also related to faunal composition. Riffles varied in both faunal densities and near-bed flow environment, but not in any consistent way. Such variability means that individual riffles cannot be reasonably used to ‘represent’ stream sections or orders, an assumption commonly made in stream studies. Neglect of such issues has also resulted in poor conceptual integration between large- and small-scale studies in stream ecology.     

Using rarity to infer how dendritic network structure shapes biodiversity in riverine communities

Dispersal of organisms connects physical localities, but the strength of connection varies widely. Variability in the influence of dispersal can be predictable in sharply defined networks like river systems because some sections of the network are more isolated, leading to different balances of local (i.e. environmental filtering, species interactions) and regional (i.e. dispersal‐driven) processes in structuring communities. We examined the influence of spatial isolation on the relative contributions of α‐ and β‐diversity to regional (γ) diversity, and examined how that influence differed between common and rare species in stream macroinvertebrate communities. One explanation for rarity on a regional scale is that common species are habitat generalists while rare species are specialists. Therefore, common species should be influenced more by dispersal‐driven processes while rare species should be more influenced by local processes. We predicted that for rare taxa, β‐diversity should represent a higher fraction of γ‐diversity in isolated headwaters but that differences between rare and common taxa with regard to the contribution of β‐diversity to γ‐diversity should be less distinct in well‐connected mainstem habitats. To test these predictions, we used macroinvertebrate communities from 634 sites across 22 watersheds. Regardless of rarity, β‐ and γ‐diversity were higher in headwaters compared to mainstems. However, α‐diversity was similar regardless of isolation for rare assemblages. But contrary to our predictions, common assemblages of predators and herbivores did exhibit differences in α‐diversity between locations. Our predictions were strongly supported for two guilds of consumers, the detritivores and collectors, but less so for herbivores and predators. However, these results make sense considering differences in life histories between the groups. For detritivores and collectors, species turnover (β‐diversity) was higher in isolated regions in river networks, and rarity exacerbated this effect, resulting in higher regional diversity of rare species, supporting the general theory that rarity reflects habitat specialization.     

Rareness starts early for disturbance-dependent grassland plant species

Ecological communities always contain a few common species and an abundance of uncommon species. Given that most plant mortality occurs in seeds and seedlings, recruitment success often predicts plant community assemblage and patterning, but observational patterns do not reveal whether plant populations are seed or habitat limited. Grassland plant species make up a sizable portion of the overall native flora in northeastern North America (N.A.), but approximately 30 % of the area’s threatened and endangered flora are grassland species, possibly leftovers from the post-glacial landscape. Yet, close relatives of many rare grassland species thrive in the same range. We investigated whether seed or habitat limitation explained rarity and commonness in remnant grassland species. We used seed addition experiments coupled with microhabitat manipulations (burning and herbivore exclusion) in three different habitat types to evaluate recruitment (germination and seedling survival) limitation for three rare and three common grassland species. Rare grassland species successfully recruited where burning reduced initial competitor density, but seedling survival suggested they were severely limited by interspecific competition. Both the rare and common plant species survived equally well in forest habitats where herbaceous density was low whereas neither survived in the edge habitats. Only the common plants thrived in the high-competition meadow habitat, further suggesting that the rare grassland species are poor competitors. Commonness and rarity are temporal designations that can change as disturbance alters the landscape. Glacial retreat and low precipitation in northeastern N.A. created a landscape suitable for poor competitors that tolerated poor conditions. Our results suggest that rare remnant grassland plants, unlike their close relatives, display more biotic than abiotic limitation as they do not compete well with other plants. These results suggest that suitable habitat is not a spatial location but a temporally transient assemblage of species requirements.     

Patterns of commonness and rarity in central European birds: reliability of the core-satellite hypothesis within a large scale

The frequency distribution of species’ area of occupancy is often bimodal, most species being either very rare or very common in terms of number of occupied sites. This pattern has been attributed to the nonlinearity associated with metapopulation dynamics of the species, but there are also other explanations comprising sampling artifact and frequency distribution of suitable habitats. We tested whether the bimodal frequency distribution of occupied squares in central European birds could be derived solely from the frequency distribution of species population sizes (i.e. the sampling artifact hypothesis) or from the spatial distribution of their preferred habitats. Both models predict high proportion of very common species, i.e. the right side of frequency distribution. Bimodality itself is well predicted by models based on random placement of individuals according to their abundances but neither model predicts the observed prevalence of rare species. Even the combined models that assume random placement of individuals within the squares with suitable habitat do not predict such a high proportion of rare species. The observed distribution is more aggregated, rare species occupying a smaller portion of suitable habitat than predicted on the basis of their abundance. The pattern is consistent with metapopulation processes involving local population extinctions. The involvement of these processes is supported by two further observations. First, species rarity is associated with significant population trend and/or location on the edge of their ranges within central Europe, both situations presumably associated with metapopulation processes. Second, suitable habitats seem to be either saturated or almost unoccupied, which is consistent with the predictions of the metapopulation model based on nonlinear dynamics of extinction and colonization. Although the habitat suitability is an important determinant of species distribution, the rarity of many species of birds within this scale of observation seems to be affected by other factors, including local population extinctions associated with fragmentation of species’ habitats.     

A Large-scale Comparative Analysis of Riffle and Pool Fish Communities in an Upland Stream System

Fishes were sampled in riffle and pool habitats at 74 upland localities in the Little River system, southeastern Oklahoma and southwestern Arkansas, U.S.A. I asked how these two habitat-defined communities differed with regard to species abundance and incidence patterns, and how these differences varied along othree environmental gradients: elevation, stream gradient, and stream size. Riffle and pool communities showed distinct and significant differences when ordinated in multivariate space defined by species abundance patterns. Sites with similar pool communities did not have similar riffle communities, and riffle and pool communities responded to environmental gradients in different ways. Elevation was the best predictor of pool community structure, whereas stream size was the best predictor of riffle communities. Overall, riffle habitats had fewer species than pool habitats and formed significant subsets of pool communities at 12 of 74 sites. I predicted that at small stream localities where riffles were unstable, riffle species would form subsets of the pool species communities, and both community types should show high similarities. The presence of faunal subsets was not associated with stream size, but faunal similarities were significantly higher at small stream localities. At the species level, 14 species were significantly associated with pool habitats, while only two were associated with riffle habitats. Riffle and pool communities, although linked by a continuous habitat gradient at the local scale, responded differently to large-scale environmental gradients. Local differences between these communities were predictable based on stream size.     

The effect of habitat-specific sampling on biological assessment of water quality using a predictive model

1. Detection of impairment in macroinvertebrate communities using rapid biological assessment depends on the ability to compare sites, with confidence that differences obtained result from water quality. However, collections from more than one habitat type may introduce variation that can potentially mask water quality differences among sites. Data were collected from the riffle, edge, pool-rock and macrophyte habitats at reference (minimally disturbed) and test (disturbed) stream sites throughout the Australian Capital Territory. The effect of habitat-specific sampling on predictive models for detecting impairment in macroinvertebrate communities was determined. Four models were used: riffle only, edge only, each habitat as an individual object, and all habitats sampled at a site considered as a composite sample. 2. Macroinvertebrates from individual habitats generally clustered into separate groups because collections from the same habitat at different sites were more similar than collections from different habitats within a site. Thus, in the habitats as individual objects model, the taxa predicted to occur at a test site may be an indication of habitat type rather than water quality. The outputs of the composite habitats and riffle and edge models were similar. However, the variable number of habitats included at each site in the composite model may confound the detection of biological impairment because of unequal sampling effort. The riffle and edge models were the most robust because they were less confounded by inter-habitat variation and were based on comparisons made between equivalent environmental units. 3. Comparison of observed/expected taxa ratios for test sites showed that each model could detect biological impairment, indicating considerable data redundancy was introduced by sampling several habitats. In particular, the pool-rock and macrophyte habitats contributed no information with regard to macroinvertebrate taxon occurrence or detection of biological impairment that could not be obtained from either the riffle or edge habitats within the study area.     

The influences of habitat and seasonal sampling regimes on the ordination and classification of macroinvertebrate assemblages in the catchment of the River Wye,Wales

Assemblages of benthic macroinvertebrates were assessed in relation to environmental variables at 45 sites in the catchment of the Welsh River Wye in 1982.Samples were collected from three habitats (margins, riffles, flats) and in two seasons (Spring and Autumn), separated and combined data sets being ordinated by DECORANA and classified by TWINSPAN. Correlations between primary ordinations were high (p < 0.001) and always strongly related to total hardness or pH; secondary ordinations were also intercorrelated and were related to stream slope.In each instance, total hardness and slope were the strongest discriminants between site groupings produced by TWINSPAN. It is concluded that relationships between faunal assemblages, stream chemistry and stream physiography would be effectively detected in the Wye catchment in either Spring or Autumn and in each of the habitats sampled. However, the most precise categorization of assemblage type required a sampling strategy which combined habitat and seasonal data.     

Drivers and interrelationships among multiple dimensions of rarity for freshwater fishes

Species can be rare or common in three different dimensions: geographic range size, habitat breadth, and local abundance. Understanding drivers of rarity are not only fundamentally interesting; it is also pertinent for their conservation. We addressed this challenge by analyzing the rarity of 291 native freshwater fishes occurring in ca 3500 independent stream reaches that span a broad environmental gradient across continental USA. Using phylogenetic regression and path analysis, we examined the concordance among the three rarity dimensions, and identified possible mechanisms by which species life‐history, habitat affinities, and biogeography drive variation in rarity. Weak double extinction jeopardies were driven by weakly positive correlations between habitat breadth and local abundance, and between habitat breadth and geographic range size. However, a triple extinction jeopardy was averted as local abundance and range size were not positively linked in our study. This is because large‐river and lacustrine habitat use mediated a trade‐off between local abundance and range size. Large rivers and lacustrine habitats represent important dispersal pathways and refugia that enabled fishes to acquire wide ranges; however, species using these habitats are less abundant overall because they are less adapted to small lotic channels, which comprise the majority of stream habitats in the US. Life‐history traits were key in governing the relationship between abundance and range size as large‐river and lacustrine habitat use were driven by body size, egg size, and parental care. Our analysis contributes novel insights into mechanisms that underlie multiple dimensions of rarity in freshwater fish and informs the prioritization of multiply rare species for conservation.     

Macroinvertebrate–habitat relationships in the River Teifi catchment and the significance to conservation

SUMMARY. 1. A macroinvertebrale survey of various habitats (e.g. riffles, pools, tree roots) at sixteen sites in the Teifi catchment in September 1981 yielded 217 taxa excluding Hydracarina and Chironomidae.
2. Sites with the greatest number of habitats were generally rich in taxa and supported the highest number of 'rare' species, the latter generally being associated with vegetation. However, species were not generally restricted to particular habitats although ecdyonurid mayflies predominated in riffles and one leptocerid caddisfly was principally collected from tree roots.
3. Four groups of taxa which characterized three habitat groups were established using classification procedures and it was concluded that three habitat types (eroding, depositing and vegetation) should be sampled to describe adequately the macroinvertebrate fauna at each site.
4. Three attributes (species richness, species rarity and site uniqueness) were used to establish the conservational value of each site; in general, the main river and one lowland tributary were of highest conservational significance.
5. Multiple regression analyses were used to establish significant relationships between the three attributes and environmental features such as number of habitats, altitude, river width, pH and total hardness. Such relationships may facilitate a rapid assessment of resource value without expensive biological survey.     

Spatial and temporal variability of macroinvertebrates in spawning and non-spawning habitats during a salmon run in Southeast Alaska

Spawning salmon create patches of disturbance through redd digging which can reduce macroinvertebrate abundance and biomass in spawning habitat. We asked whether displaced invertebrates use non-spawning habitats as refugia in streams. Our study explored how the spatial and temporal distribution of macroinvertebrates changed during a pink salmon (Oncorhynchus gorbuscha) spawning run and compared macroinvertebrates in spawning (riffle) and non-spawning (refugia) habitats in an Alaskan stream. Potential refugia included: pools, stream margins and the hyporheic zone, and we also sampled invertebrate drift. We predicted that macroinvertebrates would decline in riffles and increase in drift and refugia habitats during salmon spawning. We observed a reduction in the density, biomass and taxonomic richness of macroinvertebrates in riffles during spawning. There was no change in pool and margin invertebrate communities, except insect biomass declined in pools during the spawning period. Macroinvertebrate density was greater in the hyporheic zone and macroinvertebrate density and richness increased in the drift during spawning. We observed significant invertebrate declines within spawning habitat; however in non-spawning habitat, there were less pronounced changes in invertebrate density and richness. The results observed may be due to spawning-related disturbances, insect phenology, or other variables. We propose that certain in-stream habitats could be important for the persistence of macroinvertebrates during salmon spawning in a Southeast Alaskan stream.     

Niche position, but not niche breadth, differs in two coexisting amphibians having contrasting trends in Europe

Aim We explored general habitat‐related explanations (niche breadth and niche position) to the contrasting status of two amphibian species that have largely overlapping ranges and habitats – the rare and declining crested newt (Triturus cristatus), and the more common smooth newt (Triturus vulgaris). These closely related and ecologically similar species provide an excellent opportunity to study those methodologically challenging hypotheses, and this is the first such study on amphibians. Location Denmark. Methods We derived multivariate habitat models from 27 characteristics of 210 ponds and their surroundings, and their occupation by newts. In addition to the model performance, niche breadths were compared using the mean beta diversity of amphibian communities in the presence of each newt species. Results For each newt species, the habitat models comprised three variables and correctly classified 74% of observations. Diverse invertebrate fauna (prey base) and shorter distances to other ponds inhabited by conspecifics were positive for both species, while the surrounding habitat (notably dry grasslands with forests) was important for the crested newt and the sediment type of the pond for the smooth newt only. Beta diversity of the amphibian communities of occupied ponds did not differ between the two newt species. Hence, in an area of frequent coexistence, habitat requirements of the species differed in key variables, not in the extent of specialization. Main conclusions Our study supported the niche position rather than the niche‐breadth hypothesis of rarity. We suggest that the rarity and/or continuing decline of the crested newt is related to the degradation of (semi)natural terrestrial habitats around suitable water bodies in Europe. Consequently, special restoration of such habitats has a high potential for the recovery of this rare species, while general pond management appeared more beneficial for the common smooth newt.     

The contribution of common and rare species to plant species richness patterns: the effect of habitat type and size of sampling unit

Understanding how overall patterns of spatial variation in species richness are affected by distributional patterns of species has been an area of growing concern. In the present study, we investigated the relative importance of common and rare species as contributors in overall plant species richness. We further examined if the effects of common or rare species in richness patterns are affected by the size of the sampling units and if the observed patterns hold at different habitats. We used a dataset of 5,148 higher plant species distributed across 16,114 sampling plots located in 240 sites of the NATURA 2000 network of Greece. We ranked all species based on the number of sites they occupied and we developed a common to rare and a rare to common sequence. We correlated those sequences with cumulative species distributions. We performed this analysis in nine different sizes of sampling units and in three different datasets referring to (a) all habitat types together, (b) coniferous habitats only and (c) alpine habitats only. Our analysis showed that despite the proportionally higher numbers of restricted species, widespread species make a greater contribution to overall richness patterns and that this observed pattern does not depend on the size of the sampling units. Moreover, the observed pattern stands for different habitat types. Our findings support the generality of this pattern and highlight the importance of widespread species as adequate indicators of biodiversity patterns at various habitat types. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

长白山北坡不同海拔及干扰程度下访花食蚜蝇群落的差异

本研究采用垂直面取样法,对中国长白山北坡不同海拔及干扰程度下访花食蚜蝇群落的物种组成、多度、丰富度及多样性进行了调查研究。我们选择了不同垂直带的两个样地,分别位于800~1 100 m和1 750 ~2 150 m;每个样地选取3种生境类型,每一生境类型采样面积为20 m×20 m。252组调查数据表明,共采到访花食蚜蝇42种2 540个体。不同海拔生境访花食蚜蝇的组成、多度、丰富度及多样性的差异分析结果表明: 低海拔样地内不同生境访花食蚜蝇的群落相似性高于高海拔样地;低海拔样地访花食蚜蝇的多度高于高海拔样地,而物种丰富度低于高海拔样地;不同生境类型访花食蚜蝇多样性指数存在差异,但高海拔样地与低海拔样地多样性差异不显著;过渡林生境（岳桦林带）与次生林生境（针阔混交林带Ⅱ）中访花食蚜蝇的多样性较高。保护珍稀植物物种的人工植物花园访花食蚜蝇多样性仅次于过渡林生境（岳桦林带）与次生林生境（针阔混交林带Ⅱ）,保护作用显著。     

Assessment of river condition at a large spatial scale using predictive models

1. RIVPACS-type predictive models were developed at a relatively large spatial scale for the Australian state called New South Wales (NSW, 801 428 km²). Aquatic macroinvertebrate samples and physical and chemical data were collected from 250 reference sites (little affected by human activities) and 23 test sites (with known human impacts) throughout NSW in autumn and spring 1995 and identified mostly to family level. Reference sites were grouped based on their macroinvertebrate data using classification (UPGMA) and ordination techniques. Relationships between macroinvertebrate and environmental data were established using principal axis correlations and stepwise multiple discriminant function analysis. models for predicting invertebrate assemblages were developed separately for edge and riffle habitats for autumn and spring data sets and for combined autumn and spring data sets. 2. Sites in the lowland sections of the western flowing rivers were characterized by low taxonomic richness and were distinct from the sites in the eastern part of the state. Sites on the western slopes of the Great Dividing Range in southern and northern NSW mostly fell into separate groups. In eastern NSW, site groups did not represent a north, central and south division. Sites on highland streams, coastal fringe streams and large rivers mostly formed distinct groups, but most of the sites on east-flowing rivers fell into large site groups that did not have clear geographic boundaries. 3. Environmental variables that were strongly correlated with ordinations of macroinvertebrate presence/absence at sites were water temperature, altitude, longitude and maximum distance from source. The predictor variables determined by DFA for the six models created included alkalinity, altitude, location (longitude and/or latitude), stream size and substratum composition. These are generally in common with the variables determined for other large geographic areas in Australia and the United Kingdom. 4. Model outputs from reference sites suggest that, among the six models, the riffle model combining autumn and spring is likely to give the most reliable predictions. The combined edge model also performed well but refinements are needed for single season models to provide reliable outputs. 5. Combined season models both for riffles and for edges detected biological impairment at all but one of the test sites. Single season riffle models also detected impairment while single season edge models characterized sites as unimpaired despite other models’ indications of impaired fauna. Riffle models may be more sensitive than edge models but the sampling of riffles is often limited by flow. Edge habitats are available at most sites but there may be few riffles in floodplain rivers. Available resources, desired model sensitivity, and river type should be considered jointly to determine the most useful habitat to sample.     

Fish habitat association in an Ozark stream

Synopsis Associations of fishes in physically distinct habitats (riffles, inlets and pools) of Flint Creek were studied to evaluate critically the habitat-guild concept — the notion that fishes associate with patches of stream habitat in discrete groups. There was little evidence of significant interspecific association at the habitat level. Most fishes were very generalized in their habitat-use patterns. Faunal similarity between habitats was unrelated to physical-habitat similarity. Assemblages from physically distinct habitats were little different from those from physically similar habitats. The structure of the associations (constancy within groups of commonly occurring species) varied seasonally and from site to site. There were constant associations in pools from summer through fall and this coincided with conditions of high fish density and low food availability, suggesting that the pattern resulted from past or present interaction between species. However, the timing also coincided with recruitment of young. Pools were the favored habitats of young-of-year fishes which dominated assemblages in these areas during summer and fall months. This apparently adaptive pattern of habitat association, operating in tandem with local reproductive success could have been responsible for the constancy observed in pools. Most of the species considered here made use of a variety of habitat conditions over the course of their life histories. Individual patches of habitat satisfied the needs of few fish, and thus, seemed too small a scale for the study of community-assembly mechanisms. There was better evidence of interspecies association at the scale of two or more of these habitat areas combined.