Macroinvertebrate richness patterns in North African streams

Aim To test the hypothesis that macroscale environmental variables explain local taxonomic richness of stream macroinvertebrates, and then to identify the relationships between these variables and benthic fauna richness in North Africa. Location North Africa, from West Morocco to East Tunisia. Methods Using a large‐scale data base made of 211 sampling sites gathered from an area of 500,000 km², an artificial neural network model has been built to identify and predict the influence of macroscale environmental variables on local macroinvertebrate richness. Results The correlation coefficient (r) between observed and estimated taxon richness values was 0.75 (P < 0.001), and the model explained more than 55% (r² = 0.563) of the macroinvertebrate richness variation. Macroinvertebrate richness was, therefore, accurately predicted using only three environmental variables accounting for hydrology (number of rainy days), geographical factors, i.e. connections between European and North African land masses (longitude) and climatic gradient (altitude). Main conclusions Stream macroinvertebrate richness in North Africa results from a combination of climatic, geographical and hydrological parameters. Although consistent with current biogeographic and ecological concepts mainly derived from European and North American streams, this study underlines the specificity of dry Mediterranean ecosystems. The shape of diversity patterns results from climatic conditions and their associated environmental seasonal dynamics, which screens geographical processes.     

Macroinvertebrate assemblages in Andean Patagonian rivers and streams: environmental relationships

Macroinvertebrate communities from 29 streams and rivers of the mountain and the Andean Patagonian Plateau were analyzed. Samples were collected from six river basins, which were part of four different biozones of the Patagonian Ecoregion. Samples from mountain streams were dominated by Plecoptera, Ephemeroptera, Trichoptera and Diptera, while plateau rivers where mainly Diptera, Oligochaeta and Mollusca. Total invertebrate abundance ranged from 7 to 12249 ind.m^–2. Elmidae, Paratrichocladius, Chironomus, Smicridea annulicornis, Parasericostoma ovale and Meridialaris laminata were the most abundant insect taxa, while Nais communis and Hyalella curvispina were the most abundant non-insect taxa. Species-environmental relationships were examined using Canonical Correspondence Analysis. Current speed, conductivity, substrate size and abundance of aquatic plants, were identified as the major variables structuring faunal assemblages. Regression analyses revealed that species richness was negatively correlated with latitude, and positively correlated with water temperature and altitude. Macroivertebrate abundance increased with conductivity, altitude and water temperature. These results suggest that habitat heterogeneity was the strongest predictor of macroinvertebrate assemblages, but species richness could be predicted at a landscape scale using topographical and climatic features.     

The effect of partial and total drought on the macroinvertebrate communities of three small Danish streams

Three cases of partial or total drought were studied. A two weeks' stop of water flow with reduced water level and stagnant water was survived by most stream species. Only the population of Baetis rhodani Pict. was almost eliminated. An unprecedented drought of 2-3 months reduced numbers of stream species. The differential effects are discussed in relationship to the behaviour, life cycle and physiology of the individual species. After the drought many invaders were found, but most disappeared rapidly. Only Asellus aquaticus L. maintained a population in the stream. In an intermittent stream with 3–4 months' drought no changes were observed, and many species were the same as those which survived in the second stream. It is concluded that the consequences of an increasing frequency of drought, for example due to increasing ground water use, will depend on the species normally present and on the season and duration of the drought.     

Distribution of benthic algae and macroinvertebrates along a thermal stream gradient

The distribution and abundance of benthic algae and macroinvertebrates were examined along a natural thermal gradient formed by hot springs in Little Geysers Creek, Sonoma Co., California, USA. Maximum water temperatures ranged from 52 °C at the uppermost station to 23 °C at a station 400 m downstream. Benthic chlorophyll a decreased exponentially from 2.5 g m^–2 at 52 °C to less than 0.1 g m^–2 at 23 °C, a pattern of decline also exhibited by algal phaeophytin. Blue-green algae dominated at higher temperatures but were replaced by filamentous green algae and diatoms at lower temperatures.Macroinvertebrates were absent at temperatures 45 °C; the highest density (> 150 000 m^–2, mainly Chironomidae) occurred at 34 °C, whereas biomass was highest (4.6 g m^–2, as dry weight) at 23 °C and species richness (15 species) was highest at 27 °C. The two predominant macroinvertebrate populations (the midge Tanytarsus sp. and the caddisfly Helicopsyche borealis) occurred at sites that were several degrees below their lethal thermal threshold, suggesting that a temperature buffer is maintained.     

Macroinvertebrate colonization of stones in two upland southern Australian streams

Experiments on the colonization by macroinvertebrates of stones were performed in the Acheron and Toorongo Rivers, two upland rivers in south-eastern Australia. The three experiments were each about one month in duration. In the first experiment — Acheron I — and the third experiment — Toorongo — river stones were used. In the Acheron II experiment both river stones and quarry stones were used.The number of colonizing species with time in the Acheron I and Toorongo experiments fitted a logarithmic model with the colonization and elimination (extinction) rates both declining with time. The population densities of the total animals and of most of the common species fitted the power model (linear model on logarithmically transformed axes). In the Acheron II experiment the major difference between the colonization of river stones and quarry stones was the low numbers of scrapers on the quarry stones. The colonization of the stones in Acheron I and Toorongo by the various functional feeding groups is described. The colonization of stones in streams is a rapid process suggesting that the stream stone assemblage has a high resilience — an attribute of deterministic communities.     

Macroinvertebrate identity mediates the effects of litter quality and microbial conditioning on leaf litter recycling in temperate streams

Plant litter decomposition is an essential ecosystem function that contributes to carbon and nutrient cycling in streams. Aquatic shredders, mainly macroinvertebrates, can affect this process in various ways; they consume leaf litter, breaking it down into fragments and creating suitable habitats or resources for other organisms through the production of fine particulate organic matter (FPOM). However, measures of litter‐feeding traits across a wide range of aquatic macroinvertebrates are still rare. Here, we assessed the contributions of 11 species of freshwater macroinvertebrates to litter decomposition, by measuring consumption rate, FPOM production, and assimilation rate of highly decomposable (Alnus glutinosa) or poorly decomposable (Quercus robur) leaf litter types. In general, an increase in the quality of litter improved the litter consumption rate, and fungal conditioning of the leaf litter increased both the litter consumption rate and FPOM production. Macroinvertebrates specializing in leaf litter consumption also appeared to be the most sensitive to shifts in litter quality and the conditioning process. Contrary to expectations, the conditioning process did not increase the assimilation of low‐quality litter. There was a strong correlation between the relative consumption rate (RCR) of the two litter types, and the relative FPOM production (RFP) was strongly correlated to the RCR. These findings suggest a consistent relationship between RCR and macroinvertebrate identity that is not affected by litter quality, and that the RFP could be inferred from the RCR. The varying responses of the macroinvertebrate feeding traits to litter quality and the conditioning process suggest that the replacement of a shredder invertebrate species by another species could have major consequences for the decomposition process and the detritus‐based food web in streams. Further studies onto the importance of invertebrate identity and the effects of litter quality in a variety of freshwater ecosystems are needed to understand the whole ecosystem functioning and to predict its response to environmental changes.     

Setting Attainable Goals of Stream Habitat Restoration from a Macroinvertebrate View

Many efforts have been undertaken to reduce the impairment of stream ecosystems by wastewaters and other pollution, leading to a remarkable improvement of the water quality in most parts of Central Europe. Actually, the most severe disturbance to stream systems in Central Europe is the structural degradation of stream morphology. Restoration practices increasing the structural heterogeneity of formerly degraded stream sections are necessary to create new habitats at different scales that could provide habitat for a diverse invertebrate community. Increasing biodiversity of aquatic invertebrates strengthens the ecological integrity of streams and is therefore a desirable goal in stream restoration. Nevertheless, recent studies focusing on the effect of structural restoration of stream sections often displayed results that did not really met the preset goal of increasing invertebrate diversity. This might be due to sometimes severe disturbance caused by the restoration practice itself, impairing the established invertebrate community in the restored stream section. Additionally, the potential for immigration of new species into the restored stream section is often limited. Therefore, several important prerequisites must be accounted for in the planning of restoration practices to improve structurally degraded stream sections, when the goal of restoration is increasing invertebrate diversity.     

Macroinvertebrate distribution in streams: a comparison of CA ordination with biotic indices

Macroinvertebrates were collected in running waters in Italy, analyzed with correspondence analysis (CA) and with the calculation of 8 biotic indices. Then the CA ordination axes were correlated with 19 environmental variables and with biotic indices.The first CA axis is easily interpreted as an upstream-downstream gradient and is correlated with physical factors (particle size, slope etc.), whereas the second axis separated permanent waters from temporary ones.The first CA axis correlated with many biotic indices suggesting that biotic indices are strongly influenced by physical factors. Multiple regressions with 2 biotic indices as criterion and the 19 environmental factors as predictor variables confirm the importance of physical factors in determining the values of the biotic indices.The advantages and drawbacks of the use of CA instead of biotic indices is discussed.     

Identification of linear and threshold responses in streams along a gradient of urbanization in Anchorage, Alaska*

We examined biotic and physiochemical responses in urbanized Anchorage, Alaska, to the percent of impervious area within stream basins, as determined by high-resolution IKONOS satellite imagery and aerial photography. Eighteen of the 86 variables examined, including riparian and instream habitat, macroinvertebrate communities, and water/sediment chemistry, were significantly correlated with percent impervious area. Variables related to channel condition, instream substrate, water chemistry, and residential and transportation right-of-way land uses were identified by principal components analysis as significant factors separating site groups. Detrended canonical correspondence analysis indicated that the macroinvertebrate communities responded to an urbanization gradient closely paralleling the percent of impervious area within the subbasin. A sliding regression analysis of variables significantly correlated with percent impervious area revealed 8 variables exhibiting threshold responses that correspond to a mean of 4.4 – 5.8% impervious area, much lower than mean values reported in other, similar investigations. As contributing factors to a subbasin's impervious area, storm drains and roads appeared to be important elements influencing the degradation of water quality with respect to the biota.     

Macroinvertebrate community structure in relation to environmental variables in a Swiss glacial stream

1. Benthic macroinvertebrate distribution was examined in relation to channel characteristics (including stability), substratum, hydraulic variables, primary production (chlorophyll a ) and coarse particular organic matter (CPOM) in an alpine glacial stream, the Mutt (Upper Rhône valley, Switzerland). Co-inertia analysis and canonical correspondence analysis were used to identify the major environmental gradients influencing community variations.
2. The Mutt (length: 3.6 km, altitudinal range: 1800–3099 m a.s.l.) exhibited typical characteristics of a kryal stream. Average summer temperature remained below 2 °C immediately downstream from the snout but was on average 5 °C higher 1700 m downstream. Seasonal variations in water sources were evidenced by the high late-summer (September) contribution of groundwater with increased conductivity.
3. Sixty-six taxa were recorded from the five reaches sampled at three periods (snowmelt, ice melt and low water in late summer) in 1996 and 1997, of which 29 were Chironomidae. Three taxa of Diamesinae were the first colonizers of the stream below the glacier, but 16 taxa, including Ephemeroptera, Plecoptera and Trichoptera, were already recorded 200 m downstream. Water depth, channel slope and Pfankuch's Index of channel stability were strongly correlated with the longitudinal faunal gradient. Maximum temperature, current velocity and water conductivity were also correlated, but to a lesser extent.
4. The rapid incorporation of non-chironomid taxa into the stream community represented a departure from Milner & Petts's (1994) conceptual model of invertebrate succession downstream of glacial margins. The results confirmed that glacial stream communities are primarily driven by physical determinants.     

Macrobenthic invertebrate richness and composition along a latitudinal gradient of European glacier-fed streams

1. The influence of 11 environmental variables on benthic macroinvertebrate communities was examined in seven glacier-fed European streams ranging from Svalbard in the north to the Pyrenees in the south. Between 4 and 11 near-pristine reaches were studied on each stream in 1996–97.
2. Taxonomic richness, measured at the family or subfamily (for Chironomidae) levels for insects and higher levels for non-insects, increased with latitude from Svalbard (3 taxa) to the Pyrenees (29 taxa).
3. A Generalized Additive Model (GAM) incorporating channel stability [Pfankuch Index (PFAN)], tractive force, Froude number (FROU), water conductivity (COND), suspended solids (SUSP) concentration, and maximum temperature explained 79% of the total deviance of the taxonomic richness per reach. Water temperature and the PFAN of stability made the highest contribution to this deviance. In the model, richness response to temperature was positive linear, whereas the response to the PFAN was bell-shaped with an optimum at an intermediate level of stability.
4. Generalized Additive Models calculated for the 16 most frequent taxa explained between 25 (Tipulidae) and 79% (Heptageniidae) of the deviance. In 10 models, more than 50% of the deviance was explained and 11 models had cross-validation correlation ratios above 0.5. Maximum temperature, the PFAN, SUSP and tractive force (TRAC) were the most frequently incorporated explanatory variables. Season and substrate characteristics were very rarely incorporated.
5. Our results highlight the strong deterministic nature of zoobenthic communities in glacier-fed streams and the prominent role of water temperature and substrate stability in determining longitudinal patterns of macroinvertebrate community structure. The GAMs are proposed as a tool for predicting changes of zoobenthic communities in glacier-fed streams under climate or hydrological change scenarios.     

Effects of sediment releases from a reservoir on stream macroinvertebrates

Effects of sediment release from Guernsey Reservoir on macroinvertebrates of the North Platte River, Wyoming, were investigated during summer 1981. Suspended solids concentrations during sediment release increased from <20 mg l^–1 to >300 mg l^–1. Because fine particulates remained in suspension, mean particle size of substrates was unaltered. Densities of chironomids decreased 90% + during sediment release but recovered to initial levels in 3 weeks after the release ended. Densities of mayflies and oligochaetes increased. Changes in benthic populations were highly correlated with increases in suspended solids.     

A unique role for citizen science in ecological restoration: a case study in streams

Citizen science has the potential to generate valuable biologic data for use in restoration monitoring, while also providing a unique opportunity for public participation in local restoration projects. In this article, we describe and evaluate a citizen science program designed to monitor the effect of stream restoration construction disturbance on the macroinvertebrate community. We present the results of a 7‐year stream restoration study conducted by citizen scientists utilizing a Before‐After‐Control‐Impact (BACI) design. Trait‐based macroinvertebrate data showed a strong response to restoration construction disturbance and return to pre‐restoration conditions within 2 years. The findings of this study suggest that citizen science can generate meaningful BACI‐oriented data about ecological restoration; however, until more research is conducted, citizen data should only be used to augment professional data intended to demonstrate restoration success.     

Macroinvertebrate stream communities along regional and physico-chemical gradients in Western Greenland

1. Macroinvertebrates were collected and physico‐chemical variables measured at 16 stream sites in Western Greenland during July 1999. Eight sites were located on Disko Island in an arctic oceanic climate and eight sites in the Kangerlussuaq area close to the icecap where the climate is arctic continental. The streams had different water sources (glacial, groundwater, snowmelt and lake water). 2. The streams showed pronounced differences in water temperature (2.2–17.3 °C), concentrations of suspended solids (0–2400 mg L^?1), and conductivity (10–109 μS cm^?1). Principal component analysis (PCA) analysis of the physico‐chemical variables separated the Disko Island sites into a distinct group, whereas the sites in the Kangerlussuaq area were more dispersed. 3. A total of 56 macroinvertebrate species were found, including 31 species of Chironomidae, the most abundant of which was Orthocladius thienemanni. Diamesa sp. was only the sixth most abundant chironomid taxon. Species composition varied between sites, and abundance varied from about 20 individuals m^?2 in a glacier fed stream to more than 16 000 m^?2 in a lake outlet. 4. The macroinvertebrate communities of the 16 streams were separated into five TWINSPAN groups reflecting water source, irrespective of region. Lake outlets and ground‐water‐fed streams had the highest species richness and abundance, temperature and bed stability, while glacier‐fed streams were characterized by low species richness, abundance, temperature, bed stability and high concentrations of suspended solids. Macroinvertebrate species richness was positively correlated with water temperature and negatively with bed stability. Conductivity was positively correlated with invertebrate abundance. 5. The results of this study suggest that the source of stream water can be used to predict invertebrate community composition in Greenlandic streams and thus the effects of changes in water balance and flow regime, and to identify sites of special conservation interest.     

Spatial scale and ecological relationships between the macroinvertebrate communities of stony habitats of streams and lakes

1. Comparative studies of distinct, but not ecologically isolated, systems such as lakes and streams may improve our understanding of the importance of ecological linkages in aquatic ecosystems. 2. In this study we compared the macroinvertebrate benthos of stony habitats in Swedish lakes and streams. Community composition was used to evaluate zoogeographic patterns and functional feeding guilds were used to identify mechanisms potentially affecting such patterns. 3. Stream communities were generally more diverse and species‐rich and had a higher proportion of grazers, shredders and passive‐filter feeders than lakes. Lake communities had a higher proportion of predators and collector‐gatherers. Of the 10 most common taxa, only Leptophlebia mayflies, clams (Sphaeriidae) and the isopod Asellus aquaticus were recorded in both lakes and streams. 4. Among‐site variance in macroinvertebrate communities accounted for by regional‐scale variables was low (6.4% for lakes and 10.1% for streams), compared with that by local‐scale variables (21% for lakes and 37.6% for streams). For lakes, the among‐site variance in macroinvertebrate communities was best explained by habitat‐scale characteristics followed by ecosystem, riparian, catchment, geographic position and ecoregion. For streams, the variance in macroinvertebrate communities was best explained by ecosystem characteristics followed by habitat, catchment, riparian, ecoregion and geographic position. 5. Conspicuous differences in spatial pattern were revealed between lakes and streams. For lakes, the most unequivocal differences in community composition and function occurred at the transition zone between the mixed forests in the south and the boreal coniferous forests in the north. Surprisingly, streams did not respond as strongly to profound landscape‐level differences in climate and vegetation cover. 6. The spatial differences noted between macroinvertebrate communities of lakes and streams may be because of differences in retention of detrital matter. Our findings imply that detrital inputs are qualitatively similar, but that the retention and processing of coarse particulate organic matter was presumably higher in lake littoral regions than in stream riffle habitats. 7. Although our findings support the conjecture that species distribution is determined fundamentally by conditions prevailing at the local‐scale, regional factors such as land use/type and the role of history were important and seemingly act as strong determinants of large‐scale patterns in biodiversity.     

Macroinvertebrate community response to natural and forest harvest gradients in western Oregon headwater streams

1. To examine the effects of forest harvest practices on headwater stream macroinvertebrates, we compiled a 167 site database with macroinvertebrate, fish, physical habitat and catchment land cover data from the three forested ecoregions in western Oregon. For our analysis, headwater streams were defined by catchment areas <10 km² and perennial water during summer low flows. Almost all sites in the database were selected using a randomised survey design, constituting a representative sample of headwater streams in these ecoregions. 2. Macroinvertebrate taxonomic and functional feeding group composition were very similar among the three ecoregions in the study area (Coast Range, Cascades and Klamath Mountains). On average, 55% of the individuals at each site were in the orders Ephemeroptera, Plecoptera or Trichoptera. Dipteran taxa (mostly chironomids) accounted for another 34%. At almost all sites, non‐insects made up <10% of the macroinvertebrate assemblage. Almost half (49%) of the assemblages were collectors; remaining individuals were about evenly divided among scrapers, shredders and predators. 3. There were 189 different macroinvertebrate taxa at the 167 sites with richness at individual sites ranging from 7 to 71 taxa. Ordination by non‐metric multidimensional scaling revealed a strong association between % Ephemeroptera, especially Baetis, and site scores along the first axis. This axis was also strongly related to % coarse substratum and fast water habitat. The second axis was strongly related to % intolerant individuals, site slope and altitude. No strong relationships were evident between any ordination axis and either logging activity, presence/absence of fish, catchment size or ecoregion. 4. Based on macroinvertebrate index of biotic integrity (IBI) scores, 62% of the sites had no impairment, 31% of the sites had slight impairment and only 6% of the sites had moderate or severe impairment. IBI scores were not strongly related to forest harvest history. All four severely impaired sites and five of the seven sites with moderate impairment were lower altitude, shallower slope stream reaches located in the Coast Range with evidence of agricultural activity in their catchment or riparian zone. % sand + fine substratum was the environmental variable most strongly related to macroinvertebrate IBI.     

Macroinvertebrate species and assemblages in the headwater streams of the River Tyne,northern England in relation to land cover and other environmental variables

The macroinvertebrate species and assemblages of headwater streams of the River Tyne catchment in northern England were classified and their relationship with environmental variables based on stream structure, water acidity, distance from source and land cover investigated using constrained ordination and logistic regression. Fuzzy classification of data from 322 stream sites generated five assemblages. Stream structure, quantified as an exposure index, was found to be the most important environmental variable, with water acidity also important. Distance from source and land cover had less influence on species and assemblage distribution. A considerable amount of variation in assemblage distribution was explained using a two-variable logistic regression with stream structure (exposure index) and water acidity (pH) in a template. Site structure and water acidity appeared to be related to drift, geology and topography with little anthropogenic influence. The applicability of the habitat template concept for explaining the distribution of stream macroinvertebrates is discussed.     

Spatial variability in macroinvertebrate assemblages along and among neighbouring equatorial glacier‐fed streams

1. During the past two decades, understanding of the structure and function of glacier‐fed stream ecosystems at temperate latitudes has increased substantially. In contrast, information on their tropical counterparts is very limited. We studied three neighbouring glacier‐fed streams in the tropical Andes of Ecuador. Our main goals were (i) to determine overall longitudinal patterns in density, taxon richness and the composition of macroinvertebrate assemblages and driving factors in equatorial glacial streams and (ii) to examine variability among replicate streams in faunal metrics and assemblages, and stream‐specific effects of supposed environmental key factors. 2. We measured four geographical and 17 environmental factors and collected five Surber samples (500 cm²) of macroinvertebrates at each of nine sites, three sites along three streams. The streams were located 1–5 km apart. In each stream, the three sites were placed at comparable distances from the glacier and were grouped as ‘upper’ (50–200 m), ‘middle’ (1.5 km) and ‘lower’ sites (3.5–5.6 km). 3. In total, 2200 individuals (64% chironomids) were collected and 47 taxa (30 dipterans, 18 of these Chironomidae) identified. Density ranged from 176 to 372 ind. m^?2, and the number of taxa ranged from 2 to 6 at the upper sites and 868–3044 ind. m^?2 and 21–27 taxa at the lower sites. Density, number of taxa, rarefied richness and axis‐1 coordinates from a MDS ordination increased logarithmically with distance from the glacier. These faunal metrics were equally related to altitude and glacier per cent of catchment and correlated with maximum conductivity, mean temperature, mean daily maximum temperature and a channel stability index. As expected, the mean difference in distance decay in similarity was higher at the upper (47% km^?1) than at the lower reaches (20% km^?1) of the streams. 4. The number of taxa varied among sites within the upper and middle groups, but not among the lower sites. In contrast, but in accordance with our expectation, assemblage composition did not differ among upper sites but did so at middle and lower sites, following a supposed decrease in environmental harshness along the streams. Relationships between faunal metrics and the four environmental variables mean temperature, the stability index, chlorophyll a and coarse particulate organic matter also varied among the three streams. Generalised linear model analyses revealed that temperature interacted with stream on macroinvertebrate density, while chlorophyll a had a significant effect on the number of taxa in interaction with stream and stability. 5. The basic predictions of the Milner et al. (2001a) , model regarding longitudinal faunal patterns and temperature and stability as main driving factors were met by our three replicate equatorial glacial streams. Qualitative departures from the model were mainly because of zoogeographical differences. We demonstrated that variability in assemblages between comparable sites in closely situated streams was considerable, and the effect of key environmental factors varied among streams and interacted with other factors. Quantifying spatial variation in benthic assemblages may help us foresee possible consequences for biodiversity as a result of glacial retreat.     

Functional Differences Among Benthic Macroinvertebrate Communities in Reference Streams of Same Order in a Given Biogeographic Area

Ecological theory (Southwood, 1977. Journal of Animal Ecology 46: 337–365, 1988. Oikos 52: 3–18; Townsend, 1989. Journal of the North American Benthological Society 8: 36–50; Townsend & Hildrew, 1994. Freshwater Biology 31: 265–275) considers that spatio-temporal variations in habitats act as evolutionary forces on organisms, selecting for traits that maximize fitness. As a consequence, communities developed under same environmental conditions should present the same combination of species bio-ecological characteristics. The objective was to verify, using data from the same biogeographical zone, (1) if there was a unique suite of bio-ecological profiles for reference macrobenthic communities of `comparable' rivers or (2) if the distribution of bio-ecological traits within reference communities was significantly influenced by geology. The variability of 22 bio-ecological traits in 12 different sites was tested to evaluate the potential influence of geological substrate on biological and ecological features of reference stream communities. Observed patterns suggested that communities displayed highly stable bio-ecological profiles among sites (within a given biogeographical zone) whatever the substrate was, even if communities on clayey substrate exhibited slightly different bio/ecological characteristics than on others geologies. Nevertheless, the functional structure of macrobenthic communities in reference sites was quite stable in this biogeographical area. This study was restricted to the selected stream types and its results may not directly be transferred to other biogeographical areas and stream types. However, the perspective of a unique functional reference for streams of the same order in a given biogeographical area, improve functional comparison between observed vs. reference communities. This could simplify and objectively define the ecological status of a given site.     

Drivers of beta diversity of macroinvertebrate communities in tropical forest streams

1. There has recently been increasing interest in patterns of beta diversity but we still lack a comprehensive understanding of these patterns in various regions (e.g. the tropics), ecosystems (e.g. streams) and organism groups (e.g. invertebrates). 2. Our aim was to investigate the patterns of beta diversity of stream macroinvertebrates in relation to key environmental (i.e. stream size, pH and habitat degradation) and geographical variables (i.e. latitude, longitude, altitude) in a tropical region. We surveyed a total of 8–10 riffle sites in each of 34 streams (altogether 337 riffle sites were sampled) in Peninsular Malaysia to examine variation in macroinvertebrate community composition at within‐stream and among‐stream scales. 3. Based on test of homogeneity of dispersion, we found that the streams studied differed significantly in within‐stream variation in community composition (i.e. among‐site variation of within stream beta diversity). The patterns were similar based on Bray–Curtis coefficient on abundance data, Sorensen coefficient on presence–absence data and Simpson coefficient on presence–absence data. We also found that within‐stream beta diversity was significantly related to stream size, pH and latitude, with each of these variables individually accounting for around 20% of the variation in beta diversity in simple regressions, while the total variation explained by the three significant variables amounted to around 50% in multiple regressions. By contrast, habitat degradation, longitude and altitude were not significantly related to beta diversity. We also found that the factor drainage basin accounted for much of the variation in beta diversity in general linear models, suppressing the effects of environmental variables. 4. We concluded that within‐stream beta diversity is mainly related to a combination of the identity of a drainage basin and stream environmental factors. Our findings provide important background for stream environmental assessment and conservation planning by emphasising that (i) macroinvertebrate communities within streams are not homogeneous, but show considerable beta diversity, (ii) streams differ in their degree of within‐stream beta diversity, (iii) stream size and water pH should be considered in applied contexts related to within‐stream beta diversity and (iv) historical effects may be different in different drainage basins and may affect present‐day patterns of within‐stream beta diversity.