The stability–diversity relationship in stream macroinvertebrates: influences of sampling effects and habitat complexity

1. Theory predicts that the stability of a community should increase with diversity. However, despite increasing interest in the topic, most studies have focused on aggregate community properties (e.g. biomass, productivity) in small‐scale experiments, while studies using observational field data on realistic scales to examine the relationship between diversity and compositional stability are surprisingly rare. 2. We examined the diversity–stability relationship of stream invertebrate communities based on a 4‐year data set from boreal headwater streams, using among‐year similarity in community composition (Bray–Curtis coefficient) as our measure of compositional stability. We related stability to species richness and key environmental factors that may affect the diversity–stability relationship (stream size, habitat complexity, productivity and flow variability) using simple and partial regressions. 3. In simple regressions, compositional stability was positively related to species richness, stream size, productivity and habitat complexity, but only species richness and habitat complexity were significantly related to stability in partial regressions. There was, however, a strong relationship between species richness and abundance. When abundance was controlled for through re‐sampling, stability was unrelated to species richness, indicating that sampling effects were the predominant mechanism producing the positive stability–diversity relationship. By contrast, the relationship between stability and habitat complexity (macrophyte cover) became even stronger when the influence of community abundance was controlled for. Habitat complexity is thus a key factor enhancing community stability in headwater streams.     

Effects of a natural flood disturbance on species richness and beta diversity of stream benthic diatom communities

Natural hydrological disturbances in streams may reduce biomass and species richness and change community composition within streams. Disturbances can also affect beta diversity among streams if their effects are species specific or vary across sites. We investigated the effect of a natural flood on species richness, community composition and among-streams beta diversity of benthic diatoms (total community and three functional groups: low profile, high profile and motile) of seven streams in New Zealand. Sampling occurred shortly before, 10 days after and 40 days after the flood. Species richness of the total diatom community did not change after the flood. The high-profile group was the only one whose species richness declined after the flood, whereas species richness of the low-profile group increased. Community composition changed after the flood, mostly as a result of species replacement rather than richness differences over time. Finally, among-streams beta diversity did not change after the flood, suggesting that variation in species composition of benthic diatoms among streams may be maintained in the face of flood disturbances.     

Microbial community diversity and composition varies with habitat characteristics and biofilm function in macrophyte‐rich streams

Biofilms in streams play an integral role in ecosystem processes and function yet few studies have investigated the broad diversity of these complex prokaryotic and eukaryotic microbial communities. Physical habitat characteristics can affect the composition and abundance of microorganisms in these biofilms by creating microhabitats. Here we describe the prokaryotic and eukaryotic microbial diversity of biofilms in sand and macrophyte habitats (i.e. epipsammon and epiphyton, respectively) in five macrophyte‐rich streams in Jutland, Denmark. The macrophyte species varied in growth morphology, C:N stoichiometry, and preferred stream habitat, providing a range in environmental conditions for the epiphyton. Among all habitats and streams, the prokaryotic communities were dominated by common phyla, including Alphaproteobacteria, Bacteriodetes, and Gammaproteobacteria, while the eukaryotic communities were dominated by Stramenopiles (i.e. diatoms). For both the prokaryotes and eukaryotes, the epipsammon were consistently the most diverse communities and the epiphytic communities were generally similar among the four macrophyte species. However, the communities on the least complex macrophyte, Sparganium emersum, had the lowest richness and evenness and fewest unique OTUs, whereas the macrophyte with the most morphological complexity, Callitriche spp., had the highest number of unique OTUs. In general, the microbial taxa were ubiquitously distributed across the relatively homogeneous Danish landscape as determined by measuring the similarity among communities (i.e. Sørensen similarity index). Furthermore, we found significant correlations between microbial diversity (i.e. Chao1 rarefied richness and Pielou's evenness) and biofilm structure and function (i.e. C:N ratio and ammonium uptake efficiency, respectively); communities with higher richness and evenness had higher C:N ratios and lower uptake efficiency. In addition to describing the prokaryotic and eukaryotic community composition in stream biofilms, our study indicates that 1) physical habitat characteristics influence microbial diversity and 2) the variation in microbial diversity may dictate the structural and functional characteristics of stream biofilm communities.     

Relationships between benthic biota and hydrological indices in New Zealand streams

1. The objective of this study was to identify the most ecologically relevant hydrological indices for characterizing hydrological regimes in New Zealand streams. To do this we related measures of periphyton chlorophyll a, ash-free dry mass (AFDM), species richness, and diversity and invertebrate density, species richness and diversity, to thirty-four hydrological variables derived from daily flow records at eighty-three sites. The hydrological variables included some describing average flow conditions, flow variability, floods, and low-flow characteristics. 2. A principal components analysis showed that the interrelationship between many of the hydrological variables was high, and most variables correlated significantly with Principal Component 1 (PC1). The flood frequency variables formed a distinct component of the flow regime and were the main contributor to PC2. 3. We found that both the average flow conditions and some measure of variability were significantly related to most of the biological variables, and these individual hydrological variables were more strongly correlated to the biological measures than the composite principal components. Only four of the thirty-four flow variables were significantly correlated (P < 0.05) with measures of periphyton biomass (chlorophyll a and AFDM), whereas twenty-four variables were correlated with periphyton diversity. Conversely, thirty-one of the thirty-four flow variables were correlated with total invertebrate density, whereas only four variables correlated with diversity. 4. We selected the flood frequency (FRE₃), where a flood is defined as flows higher than three times the median flow, as the most ecological useful overall flow variable in New Zealand streams because it explained a significant amount of the variance in four out of the six main benthic community measures, and it had a clear mechanism of control of the biota which was commensurate with current stream ecosystem theory. Periphyton biomass decreased with increasing FRE₃, whereas invertebrate density had an increasing/curvilinear relationship with FRE₃. Periphyton species richness and diversity decreased with increasing FRE₃.     

The impact of eutrophication on aquaticmacrophyte diversity in weakly mineralized streams in the Northern Vosges mountains(NE France)

The relationships between water chemistry and aquatic macrophyte species were studied in an attempt to evaluate the impact of eutrophication on aquatic macrophyte diversity in weakly mineralized streams in the Northern Vosges mountains (NE France). The macrophyte specific richness and abundance increased along an upstream to downstream zonation, which was characterized by an increase in mineralization and nutrient levels. A comparison of aquatic macrophyte diversity of two streams has shown the impact of human-induced perturbations (fish-farms, domestic sewage) in such weakly mineralized and poorly buffered waters. Disturbed sites with very high nutrient loading were characterized by a low vascular plant richness and by the presence of filamentous algae. In order to preserve the floristic diversity of weakly mineralized streams, water quality should be improved, the riverbanks restored and discharges reduced.     

Environmental thresholds and predictors of macrophyte species richness in aquatic habitats in central Europe

The degradation of habitats and species loss in freshwaters is far greater than in any other ecosystem. The decline in biodiversity has a strong potential to alter the functioning of the ecosystem and the services they provide to human society. Therefore, there is an urgent need for accurate information on patterns and drivers of diversity that could be used in the management of freshwater ecosystems. We present the results of an analysis of the relationships between macrophyte species richness and environmental characteristics using an extensive dataset collected from 160 sites in two central-European bioregions. We modelled macrophyte species richness using recursive partitioning methods to assess the diversity-environmental relationships and to estimate the environmental thresholds of species richness in rivers, streams, ditches and ponds. Several hydrological and chemical variables were identified as significant predictors of macrophyte richness. Among them, pH, conductivity, turbidity and substrate composition appeared as the most important. There is also evidence that natural ponds support a greater number of plant species than man-made ponds. Based on the detected environmental thresholds, we offer a series of simple rules for maintaining higher macrophyte species richness, which is potentially useful in the conservation and management of aquatic habitats in central Europe.     

Long-term effects of stream management on plant communities in two Danish lowland streams

Submerged macrophytes grow abundantly in most shallow streams common in the cultivated lowlands of northwestern Europe. Weed-cutting has been practised for years in many of these streams to reduce the risk of flooding of adjacent land. Our objective was to quantify long-term impacts of weed-cutting on macrophyte communities in two Danish rivers. We found that the total macrophyte coverage was similar in the weed-cut and uncut reaches in the two rivers, but species richness, diversity and patch complexity were higher in the uncut reaches. The spatial distribution of macrophytes on the stream bottom was also more heterogeneous in the uncut stream reaches. We also found evidence of a strong effect of weed-cutting on macrophyte species composition. P. natans was abundant in the uncut reaches in both streams but practically eliminated in the cut reaches, despite the fact that its basic habitat requirements were met. Also, the established phase strategy of the macrophyte community was affected by weed-cutting. Species displaying characteristically ruderal traits were more abundant in the cut reaches and species with competitive abilities were only abundant in the uncut stream reaches. We suggest that important species traits in streams, where the weed is cut regularly, are associated with rapid growth and high dispersal-capacity. Our results indicate that weed-cutting can contribute significantly to a decline in species diversity in streams. To provide optimal conditions for diverse stream macrophyte communities, we therefore suggest that weed-cutting should be minimised.     

Macrophyte communities in unimpacted European streams: variability in assemblage patterns, abundance and diversity

Macrophytes are an important component of aquatic ecosystems and are used widely within the Water Framework Directive (WFD) to establish ecological quality. In the present paper we investigated macrophyte community structure, i.e., composition, richness and diversity measures in 60 unimpacted stream and river sites throughout Europe. The objectives were to describe assemblage patterns in different types of streams and to assess the variability in various structural and ecological metrics within these types to provide a basis for an evaluation of their suitability in ecological quality assessment. Macrophyte assemblage patterns varied considerably among the main stream types. Moving from small-sized, shallow mountain streams to medium-sized, lowland streams there was a clear transition in species richness, diversity and community structure. There was especially a shift from a predominance of species-poor mosses and communities dominated by liverwort in the small-sized, shallow mountain streams to more species-rich communities dominated by vascular plants in the medium-sized, lowland streams. The macrophyte communities responded to most of the features underlying the typological framework defined in WFD. The present interpretation of the WFD typology may not, however, be adequate for an evaluation of stream quality based on macrophytes. First and most important, by using this typology we may overlook an important community type, which is characteristic of small-sized, relatively steep-gradient streams that are an intermediate type between the small-sized, shallow mountain streams and the medium-sized, lowland streams. Second, the variability in most of the calculated metrics was slightly higher when using the pre-defined typology. The consistency of these results should be investigated by analysing a larger number of sites. Particularly the need of re-defining the typology to improve the ability to detect impacts on streams and rivers from macrophyte assemblage patterns should be investigated. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

茂县土地岭植被恢复过程中物种多样性动态特征

植被恢复是退化生态系统重建的重要途径,植被恢复过程物种多样性的变化反映了植被的恢复程度.通过群落调查和多样性分析,研究了岷江上游土地岭植被恢复过程中群落物种多样性特征.结果表明： 恢复过程中6类不同类型群落分别表现其对于不同环境特征、干扰及更新方式等的响应;森林是较灌丛更适合当地环境状况的植被类型;人工恢复无干扰和轻度干扰群落的多样性相对较高,是较好的恢复模式.重度干扰使得1年生植物与地下芽植物比例增加,其它口食性较好的多年生草本减少.较强的干扰是群落无法更新、长期处于灌丛阶段且多样性较低的重要原因.本地区人工恢复群落在更新进程和多样性维持上优于自然更新群落,种植华山松加速了本地区植被演替进程.建议以适合恢复区域的多种恢复配置方式进行造林,并避免较强干扰,可以加速群落演替进程并保持恢复群落较高的物种丰富度与多样性.     

Structure and dynamics of stream fish communities in the flood zone of the lower Purus River,Amazonas State,Brazil

The structure and dynamics of fish communities were characterized by richness, abundance, diversity and stability, during high-water and low-water periods. These analyses were performed on data from the flood zone of four streams in the lower Purus River, in the Brazilian Amazon. A total of 188 species of fish were collected, distributed among 29 families and eight orders. The statistical test showed a difference in community diversity between periods. The high-water period showed higher evenness in comparison to the low-water season. The low-water period was marked by high species abundance. A great variation in community composition between the flood and low-water periods was encountered. The adjustments for species abundance models suggested that stochastic events structure the communities. Most of the species showed a temporal variation of abundance indicating low community stability. Changes in the physico-chemical conditions of the water caused by the seasonal hydrological regime may be influencing the structuring of the fish communities.     

The influence of chemistry and habitat features on the microcrustacea of some upland Welsh streams

SUMMARY. 1. Microcrustaceans were sampled during September 1990 from three microhabitats (margins, stony riffles and gravel) at thirteen stream sites in mid-Wales.
2. Patterns in the distribution, abundance and community structure of microcrustacean taxa were related to stream chemistry, physiography, substratum composition and marginal habitat structure. Patterns of distribution between microhabitats were also assessed.
3. Chemical variables were the strongest correlates with microcrustacean parameters. Total numbers of microcrustaceans and harpacticoid copepods were reduced at sites with high aluminium concentrations, and ostracods were scarce or absent at the most acidic sites. In contrast, cyclopoid copepods were more abundant and species rich at low pH.
4. Microcrustacean communities were most species rich at sites with a high percentage cover of macrophytes on the substratum. Cladoceran species richness and abundance, and the abundance of several microcrustacean species, were also positively correlated with percentage macrophyte cover.
5. Three site groupings produced by TWINSPAN classification were primarily related to percentage macrophyte cover and marginal habitat structure, with chemistry and land use also of importance.
6. Total microcrustacean abundance was highest in margins, but of all the species, only the harpacticoid Bryocamptus cuspidatus showed a strong microhabitat preference.     

Macrophyte diversity and composition in relation to substratum characteristics in regulated and unregulated Danish streams

1. The objective of the present study was to examine how the physical stream environment in regulated and unregulated lowland streams affects the diversity and distribution of macrophyte communities. We analysed the abundance, distribution and composition of macrophytes, together with physical parameters, in seven regulated and seven unregulated unshaded Danish stream reaches. 2. Total macrophyte coverage was similar in the regulated and unregulated streams, but species richness and Shannon diversity were higher in the unregulated streams. Overall, we found fifty-two different species in the regulated stream reaches and sixty-two in the unregulated stream reaches. The spatial distribution of macrophytes on the stream bottom was more heterogeneous in the unregulated streams. 3. We found positive correlations between the coverage and diversity of macrophytes and the coverage of coarse-textured substratum types on the stream bottom, as well as between macrophyte coverage and diversity and substratum heterogeneity. We also found that the macrophytes were more heterogeneously distributed where substratum heterogeneity was greater. 4. The species growing both submerged and emergent were more abundant in the regulated streams, whereas species growing only submerged were more abundant in the unregulated streams. Species growing submerged, species growing both submerged and emergent, and species only growing emergent segregated differently in a canonical correspondence analysis ordination. The submerged species were primarily associated with coarser-textured substrata, whereas species growing both submerged and emergent, and species growing only emergent were associated with finer-textured substrata. 5. The most abundant species in the regulated streams, Sparganium emersum, accounting for almost one-third of the total macrophyte coverage, was primarily associated with clay and sandy bottom substrata, whereas the most abundant species in the unregulated streams, Batrachium peltatum, was primarily associated with gravel and stony substrata.     

Structure and diversity of stream invertebrate assemblages: the influence of temperature with altitude and latitude

1. Structure and diversity of the macroinvertebrate fauna were studied in relation to altitude and latitude among three groups of streams from Ecuador (lowland: 100–600 m, Central Valley: 2600–3100 m, páramo: 3500–4000 m), and one group from the temperate lowland region of Denmark. The streams in the four regions were comparable with regard to physical characteristics such as size, current and substratum.
2. In terms of faunal composition the Ecuadorian highland streams bore more resemblance to the Danish lowland streams than the Ecuadorian lowland streams. The greater similarity between the Ecuadorian highland and the Danish streams, however, was due to the large number of insect families in the Ecuadorian lowlands, many of which were not found in the other regions. Of ten physico-chemical parameters measured, maximum stream temperature explained by far the most variability in faunal composition.
3. The number of insect orders and families increased linearly with maximum stream temperature and therefore decreased with altitude and latitude. A compilation of literature data on insect richness and maximum water temperature from streams around the world confirmed this pattern, yielding a common linear relation for both temperate and tropical streams. This pattern may arise due to a direct temperature effect on speciation but is probably also related to geological history and the influence of climatic changes on stream ecosystems. We estimate that small, tropical, lowland streams have, on average, a two- to fourfold higher species richness than temperate lowland streams.     

Seasonal dynamics of macroinvertebrate communities in a semiarid saline spring stream with contrasting environmental conditions

Semiarid saline streams are rare aquatic ecosystem types. Their constituent biota is expected to have adapted evolutionarily to strong hydrological variability and salinity stress; however, their ecology is not well known. In this study, we quantify the seasonal changes in the structure of the macroinvertebrate community in the Reventón Rambla (south-eastern Spain), a permanent saline spring stream which is included in a drainage system consisting of ephemeral dry channels (so-called “ramblas”). Seasonal patterns of community structure were studied in two reaches with contrasting environmental regimes using univariate and multivariate statistics. The upstream site showed more stable environmental conditions than the downstream site, and both sites also differed with regard to species richness, and structural and functional group attributes. On a seasonal basis, community dissimilarity was high during periods when both sites were isolated during summer droughts but dissimilarity decreased when both sites were connected through surface flow. Furthermore, the communities tended to show cyclical trajectories in multivariate ordination space. Rather than being related to salinity stress, these patterns seemed to track the hydrological disturbance regime of this rambla system. Spates tended to disrupt communities, while signs of recovery were evident during low-flow periods. Results suggest that salinity fluctuation does not pose a severe abiotic constraint to these adapted macroinvertebrate communities. Their suits of functional properties provide them with the necessary traits to recover quickly from natural disturbance. While human-caused salinization of streams severely impacts communities eventually reducing their recovery potential, our results suggest that communities in natural saline streams may show similar responses to hydrological disturbance as communities from non-saline streams.     

Effects of deforestation on fish community structure in Ecuadorian Amazon streams

SUMMARY 1. There is little information on the impacts of deforestation on the fish fauna in neotropical streams, and on parameters influencing species diversity and community structure of fish. We analysed these aspects in 12 stream sites in the Ecuadorian Amazon. The stream sites represented a large gradient in canopy cover and were located in an area of fragmented forest. While some streams had been deforested, they had not suffered gross degradation of the habitat.
2. The species richness of stream fish was not related to deforestation. Local fish diversity (Fisher's Alpha) was positively related to the surface area of stream pools (m²). Beta diversity was higher among forested than deforested sites, indicating greater heterogeneity in species composition among forested than deforested sites. The percentage of rare species was positively correlated with canopy cover.
3. Total fish density increased with deforestation, and the fish community changed from dominance by omnivorous and insectivorous Characiformes at forested sites to dominance of periphyton-feeding loricariids at deforested sites.
4. Multidimensional statistical analysis of fish community structure showed that six environmental variables (the area of stream bottom covered by leaves, relative pool area, particulate organic matter, mean depth, conductivity and suspended solids) were related to the ordination axes. The presence of leaves, which was strongly correlated to canopy cover, was the variable most closely related to fish community structure, while relative pool area was the second strongest variable. Thus, fish community structure was strongly affected by deforestation.     

The Scaling of Host Density with Richness Affects the Direction,Shape, and Detectability of Diversity-Disease Relationships

Pathogen transmission responds differently to host richness and abundance, two unique components of host diversity. However, the heated debate around whether biodiversity generally increases or decreases disease has not considered the relationships between host richness and abundance that may exist in natural systems. Here we use a multi-species model to study how the scaling of total host community abundance with species richness mediates diversity-disease relationships. For pathogens with density-dependent transmission, non-monotonic trends emerge between pathogen transmission and host richness when host community abundance saturates with richness. Further, host species identity drives high variability in pathogen transmission in depauperate communities, but this effect diminishes as host richness accumulates. Using simulation we show that high variability in low richness communities and the non-monotonic relationship observed with host community saturation may reduce the detectability of trends in empirical data. Our study emphasizes that understanding the patterns and predictability of host community composition and pathogen transmission mode will be crucial for predicting where and when specific diversity-disease relationships should occur in natural systems.     

Interactive community responses to disturbance in streams: disturbance history moderates the influence of disturbance types

Both disturbance history and disturbance type act to structure communities through selecting for particular species traits but they may also interact. For example, flooding selects for species with flood‐resistant traits in streams, but those traits could make communities susceptible to other disturbances and so could cause shifts in community composition due to anthropogenic climate change. To better understand the interactive influences of disturbance history and type on community composition, we investigated the response of macroinvertebrate communities to disturbance using in‐stream channels. Using a split‐plot design, individual channels in five ‘stable’ streams and five ‘frequently disturbed’ streams (disturbance history) were subject to different disturbance type treatments (flooding, drying and a control). Disturbance type independently drove effects on species diversity, but all other effects of disturbance type depended on disturbance history. In particular, the interaction of disturbance type and history determined overall community response. Both disturbance types tested produced similar community responses in frequently disturbed streams, including changes in community composition and alterations to the abundance of less mobile taxa, but low‐flow had a significantly greater effect in stable streams. Macroinvertebrate drift was greatest in the rock‐rolling treatments and significantly less in the low‐flow treatment for both disturbance histories. Therefore, disturbance history moderated the effects of disturbance type and determined the mechanism of community response by determining how well species were adapted to disturbance. This outcome suggests that previous disturbances strongly influence how vulnerable communities are to changes in disturbance, and so should be considered when predicting how changes in disturbance regimes will affect future community composition.     

Unravelling the determinants of stream midge biodiversity in a boreal drainage basin

1. Few extensive lotic studies have examined patterns in the biodiversity of non‐biting midges (Diptera: Chironomidae) along major environmental gradients. Our aim was to fill this gap by describing patterns in species diversity, assemblage composition and distributions of midges across a boreal drainage basin. 2. We found that the diversity of midges, as measured by rarefied species richness, Fisher’s α and Pielou’s evenness, responded positively to stream size in regression analysis. By contrast, species density was most strongly correlated to a gradient in suspended solids and phosphorus in stream water, as well as macrophyte cover. Spatial variables were not significantly correlated with species diversity. 3. Midge assemblage composition was best explained by a model incorporating five composite environmental gradients in canonical correspondence analysis. The environmental gradients were stream size, macrophyte cover, alkalinity, nitrogen and suspended solids. Spatial variables did not overcome the effects of environmental gradients on assemblage composition. 4. Cluster analysis divided the 27 study sites into four groups with relatively similar midge assemblages. These groups were statistically significant in multi‐response permutation procedure, and 15 of the 49 midge taxa recorded varied significantly among the groups in indicator value analysis. Discriminant function analysis showed that stream size, macrophyte cover and habitat structure predicted 66.7% of sites into correct groups. 5. The information provided by the present analyses may be of considerable importance in conservation planning at the drainage basin level. The fact that species diversity and assemblage composition varied primarily along the stream size gradient suggests that sites belonging to the different size classes (first to fifth order) are needed to conserve the biodiversity of midges. The other environmental gradients should also be considered in conservation planning, because they explained significant amounts of variability in midge assemblage composition.     

Macrophytes as indicators of stream condition in the wet tropics region,Northern Queensland,Australia

This study investigates the use of aquatic macrophytes as indicators of stream condition in catchments with varied land use and levels of riparian disturbance in the Wet Tropics region of North Queensland (Australia), a region of global significance in terms of faunal and floral diversity. In a paired catchment design spatial variations in macrophyte assemblage structure were characterised using multivariate and univariate techniques. Seven metrics were trialled: total macrophyte cover, species richness, % alien taxa, % native taxa, % submerged taxa, % emergent taxa and % Poaceae. Forty-four macrophyte taxa were recorded from the study area. Poaceae, Cyperaceae and mosses were the most frequently recorded taxa. Upper catchment areas in all tributaries surveyed were dominated by mosses and Cladopus queenslandicus (Domin) C.D.K. Cook (Podestemaceae). This assemblage occurred in areas with intact riparian canopy cover and good overall riparian condition. Macrophyte assemblages in lower catchment areas were distributed along gradients of riparian disturbance. Simultaneous autoregression model coefficients indicated that riparian condition had a negative influence on macrophyte cover, species richness and the proportions of alien taxa, emergent taxa and Poaceae present at sites in the Wet Tropics. Macrophyte metrics were not strongly influenced by the types of land use or water quality. These findings suggest that a riparian condition assessment would provide an adequate first assessment of the state of aquatic macrophyte assemblages in Wet Tropics streams.     

Are Chironomidae (Diptera) good indicators of water scarcity? Dryland streams as a case study

Water scarcity is becoming one of the greatest challenges that human societies will face during this century. Monitoring water availability is expensive and technically challenging. In this regard, biological communities (e.g. aquatic insects) offer a cost-effective alternative, since they integrate temporal and spatial hydrological variability.Here we explore the potential of Chironomidae (Diptera), which have been usually neglected due to their complex taxonomy, as indicators of both local habitat condition and water scarcity. The study took place in 28 sites across seven dryland streams distributed within a 400 km² section of the Upper San Pedro River basin, southeastern Arizona. The selected streams covered a wide range of hydrological variability, which was continuously measured through the deployment of 15 electrical resistance (ER) sensors. Chironomidae taxa with no drought-resistance strategies were rarely found in streams that experienced frequent drying events (i.e. intermittent and ephemeral streams), suggesting that droughts have the potential to reduce species richness due to local extinctions of drought-intolerant taxa. Intermittent and ephemeral streams registered low canopy cover and a significantly higher abundance of scrapers (which mainly feed on algae) and shredders (feeding on poorly decomposed coarse organic material). This suggests that structural changes associated to drought (e.g. reduced canopy cover and decomposition rates) might lead to changes in the functional composition of the Chironomidae assemblages. We conclude that Chironomidae species can be used as indicators of hydrological variability and the impacts of drought on streams in the absence of flow gauges.