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.     

Vulnerability of stream community composition and function to projected thermal warming and hydrologic change across ecoregions in the western United States

Shifts in biodiversity and ecological processes in stream ecosystems in response to rapid climate change will depend on how numerically and functionally dominant aquatic insect species respond to changes in stream temperature and hydrology. Across 253 minimally perturbed streams in eight ecoregions in the western USA, we modeled the distribution of 88 individual insect taxa in relation to existing combinations of maximum summer temperature, mean annual streamflow, and their interaction. We used a heat map approach along with downscaled general circulation model (GCM) projections of warming and streamflow change to estimate site‐specific extirpation likelihood for each taxon, allowing estimation of whole‐community change in streams across these ecoregions. Conservative climate change projections indicate a 30–40% loss of taxa in warmer, drier ecoregions and 10–20% loss in cooler, wetter ecoregions where taxa are relatively buffered from projected warming and hydrologic change. Differential vulnerability of taxa with key functional foraging roles in processing basal resources suggests that climate change has the potential to modify stream trophic structure and function (e.g., alter rates of detrital decomposition and algal consumption), particularly in warmer and drier ecoregions. We show that streamflow change is equally as important as warming in projected risk to stream community composition and that the relative threat posed by these two fundamental drivers varies across ecoregions according to projected gradients of temperature and hydrologic change. Results also suggest that direct human modification of streams through actions such as water abstraction is likely to further exacerbate loss of taxa and ecosystem alteration, especially in drying climates. Management actions to mitigate climate change impacts on stream ecosystems or to proactively adapt to them will require regional calibration, due to geographic variation in insect sensitivity and in exposure to projected thermal warming and hydrologic change.     

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.     

Runoff and the longitudinal distribution of macroinvertebrates in a glacier‐fed stream: implications for the effects of global warming

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Temporal changes of biodiversity in urban running waters – Results of a twelve-year monitoring study

Freshwater biodiversity underlies severe threats, mainly suffering from habitat degradation by anthropogenic land use, in particular by urbanisation. However, recent long-term studies indicate recovery of stream macroinvertebrate diversity due to improved water quality at least in North America and Europe. We monitored macroinverbrates at 56 urban stream sites over a 12-year period (2009–2020) in Braunschweig, a German urban district. We utilised these data to investigate spatio-temporal changes in taxon richness and assemblage structure as well as factors potentially affecting the resulting patterns. Overall taxon richness was increasing over the study period, comprising both all taxa and taxa being indicators for healthy stream conditions. 53.6% of the sites had significant positive trends becoming most eminent since 2014, despite decelerating since 2018, the beginning of an extra-ordinary dry period. Only 10.7% of the study sites had negative trends. Assemblage structure was shaped by environmental factors like stream width and water quality. Over-average taxon richness including positive trends and higher numbers of indicator taxa of healthy stream conditions was found in streams with higher flow velocity, good saprobic conditions and more natural streambed structure. In contrast, low taxon richness and predominance of tolerant taxa were found in streams with more degraded conditions. Most of the environmental conditions having positive effects on taxon richness were improved by various programs set up by the environmental authorities. We therefore conclude, if urban stressors like organic pollution and structural degradation can be mitigated by revitalisation and water quality improvement, urban streams can have good potential for increasing biodiversity and improving ecological functioning.     

Using modelled stream temperatures to predict macro‐spatial patterns of stream invertebrate biodiversity

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A comparison of benthic macroinvertebrate assemblages among different types of alpine streams

1. Benthic macroinvertebrate assemblages were compared among a diverse array of first‐order alpine tundra streams of the Swiss Alps. 2. A principal components analysis separated sites into three main groups: rhithral streams, rhithral lake outlets, and kryal sites including outlets and streams. Rhithral streams contained the most diverse and taxon rich assemblages, being colonised by both non‐insect taxa and Ephemeroptera, Plecoptera, Trichoptera and Diptera. 3. Rhithral lake outlets supported high densities of non‐insect taxa such as Oligochaeta, Nemathelminthes and crustaceans. Despite low taxon richness, kryal sites had high Ephemeroptera and Plecoptera abundances. Chironomidae were most common at all sites. 4. Collector‐gatherers were dominant at all sites, whereas filter‐feeders were rare. Scrapers and shredders were more common in streams than lake outlets. 5. Water temperature and algal standing crops were higher at rhithral lake outlets than rhithral streams, perhaps providing more favourable habitat for non‐insect taxa. Glacial runoff was the dominant factor influencing macroinvertebrate assemblages of kryal streams and kryal lake outlets. Alpine lakes influenced the environmental conditions of their outlets and, consequently, their macroinvertebrate assemblages unless being constrained by a glacial influence.     

Assessing streamflow characteristics as limiting factors on benthic invertebrate assemblages in streams across the western United States

1. Human use of land and water resources modifies many streamflow characteristics, which can have significant ecological consequences. Streamflow and invertebrate data collected at 111 sites in the western U.S.A. were analysed to identify streamflow characteristics (magnitude, frequency, duration, timing and variation) that are probably to limit characteristics of benthic invertebrate assemblages (abundance, richness, diversity and evenness, functional feeding groups and individual taxa) and, thus, would be important for freshwater conservation and restoration. Our analysis investigated multiple metrics for each biological and hydrological characteristic, but focuses on 14 invertebrate metrics and 13 streamflow metrics representing the key associations between streamflow and invertebrates. 2. Streamflow is only one of many environmental and biotic factors that influence the characteristics of invertebrate assemblages. Although the central tendency of invertebrate assemblage characteristics may not respond to any one factor across a large region like the western U.S.A., we postulate that streamflow may limit some invertebrates. To assess streamflow characteristics as limiting factors on invertebrate assemblages, we developed a nonparametric screening procedure to identify upper (ceilings) or lower (floors) limits on invertebrate metrics associated with streamflow metrics. Ceilings and floors for selected metrics were then quantified using quantile regression. 3. Invertebrate assemblages had limits associated with all streamflow characteristics that we analysed. Metrics of streamflow variation at daily to inter‐annual scales were among the most common characteristics associated with limits on invertebrate assemblages. Baseflow recession, daily variation and monthly variation, in streamflow were associated with the largest number of invertebrate metrics. Since changes in streamflow variation are often a consequence of hydrologic alteration, they may serve as useful indicators of ecologically significant changes in streamflow and as benchmarks for managing streamflow for ecological objectives. 4. Relative abundance of Plecoptera, richness of non‐insect taxa and relative abundance of intolerant taxa were associated with multiple streamflow metrics. Metrics of sensitive taxa (Ephemeroptera, Plecoptera and Trichoptera), and intolerant taxa generally had ceilings associated with flow metrics while metrics of tolerant taxa, non‐insects, dominance and chironomids generally had floors. Broader characteristics of invertebrate assemblages such as abundance and richness had fewer limits, but these limits were nonetheless associated with a broad range of streamflow characteristics.     

Macroinvertebrate community structure,secondary production and trophic‐level dynamics in urban streams affected by non‐point‐source pollution

1. Despite non‐point‐source (NPS) pollution being perhaps the most ubiquitous stressor affecting urban streams, there is a lack of research assessing how urban NPS pollution affects stream ecosystems. We used a natural experimental design approach to assess how stream macroinvertebrate community structure, secondary production and trophic structure are influenced by urban NPS pollution in six streams. 2. Differences in macroinvertebrate community structure and secondary production among sites were highly correlated with stream‐water specific conductivity and dissolved inorganic phosphorus (DIP) concentrations. Macroinvertebrate richness, the Shannon diversity index and the Shannon evenness index were all negatively correlated with specific conductivity. These patterns were driven by differences in the richness and production of EPT and other intolerant taxa. Production of the five most productive taxa, tolerant taxa, non‐insect taxa and primary consumers were all positively correlated with stream‐water DIP. 3. Despite the positive correlation between primary consumer production and DIP, there was no correlation between macroinvertebrate predator production and either total or primary consumer macroinvertebrate production. This was observed because DIP was positively correlated with the production of non‐insect macroinvertebrate taxa assumed to be relatively unavailable for macroinvertebrate predator consumption. After removing production of these taxa, we observed a strong positive correlation between macroinvertebrate predator production and production of available prey. 4. Our results suggest that urban NPS pollution not only affects macroinvertebrate community structure, but also alters secondary production and trophic‐level dynamics. Differences in taxon production in our study indicate the potential for altered energy flow through stream food webs and potential effects on subsidies of aquatic insect prey to riparian food webs.     

Thermal and hydrologic responses to climate change predict marked alterations in boreal stream invertebrate assemblages

Air temperature at the northernmost latitudes is predicted to increase steeply and precipitation to become more variable by the end of the 21st century, resulting in altered thermal and hydrological regimes. We applied five climate scenarios to predict the future (2070–2100) benthic macroinvertebrate assemblages at 239 near‐pristine sites across Finland (ca. 1200 km latitudinal span). We used a multitaxon distribution model with air temperature and modeled daily flow as predictors. As expected, projected air temperature increased the most in northernmost Finland. Predicted taxonomic richness also increased the most in northern Finland, congruent with the predicted northwards shift of many species’ distributions. Compositional changes were predicted to be high even without changes in richness, suggesting that species replacement may be the main mechanism causing climate‐induced changes in macroinvertebrate assemblages. Northern streams were predicted to lose much of the seasonality of their flow regimes, causing potentially marked changes in stream benthic assemblages. Sites with the highest loss of seasonality were predicted to support future assemblages that deviate most in compositional similarity from the present‐day assemblages. Macroinvertebrate assemblages were also predicted to change more in headwaters than in larger streams, as headwaters were particularly sensitive to changes in flow patterns. Our results emphasize the importance of focusing protection and mitigation on headwater streams with high‐flow seasonality because of their vulnerability to climate change.     

Landscape variables influence taxonomic and trait composition of insect assemblages in Neotropical savanna streams

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Species richness and assemblage structure of Trichoptera in Danish streams

• 1 Species richness and assemblages of Trichoptera from 157 ‘pristine’ Danish lowland stream sites were analyzed, for dependence on geographical position of the sites and simple physical variables, using two way indicator species analysis and detrended correspondence analysis.
• 2 A total of 106 species were recorded, representing ≈ 90% of the species pool known from Danish streams. Only seven species occurred at more than half the sites, whereas an additional 11 species were found at more than a quarter of the sites.
• 3 Although sites showed significant regional differences in environmental variables (stream order, width, slope and presence/absence of riparian forest), species richness and assemblages were primarily correlated with stream order, width and slope. Maximum richness was found at the largest (5th order) stream sites.
• 4 Regional differences in species assemblages were found, with several species being absent from the islands Funen and Bornholm. Species assemblages also differed between forested and non‐forested stream sites.
• 5 We found evidence that stream temperature may be of only minor importance in determining Trichoptera species richness and assemblage composition in Danish streams compared to other size‐related physical factors.

     

The influence of different spatial‐scale variables on caddisfly assemblages in Flemish lowland streams

1. Patterns in species assemblages are the result of the combined influence of processes acting on different spatial scales. Various studies describe the distribution of macroinvertebrate communities and their relationship with environmental factors at different geographical scales, but only a few of these studies concentrate on Western European lowlands. 2. Using Flanders as representative for the densely populated Western‐European lowlands, the specific aims of this study are: (i) to identify the different trichopteran species assemblages and to characterise them biologically using indicator species; (ii) to determine which environmental gradients most influence the observed species assemblages; and (iii) to analyse the relative importance of different spatial scale variables in constraining the Trichoptera distributions. 3. Assessment of the main environmental gradients suggested that the absence of Trichoptera from certain locations was mainly due to elevated nutrient concentrations and lower oxygen contents, confirming their sensitivity to anthropogenic disturbance. 4. Five Trichoptera species assemblages were distinguished based on Bray–Curtis dissimilarity coefficients. These assemblages did not differ significantly in species richness, but a shift in stream zonation preference was observed. In the ordination analysis 11 variables that were selected using a stepwise model building function manifested themselves as upstream–downstream and size‐related gradients. The Trichoptera assemblages in lowland streams thus appear to follow a longitudinal succession pattern that corresponds with the species‐specific preferences. 5. Partitioning the variance over the different spatial scales indicated that the reach‐scale variables were far more important in explaining the variation in species composition. The study design, which limited the minimum–maximum range of catchment‐scale characteristics, however, may have led to an overestimation of the impact of the local‐scale variables.     

Variability in stream macroinvertebrates at multiple spatial scales

1. We intensively sampled 16 western Oregon streams to characterize: (1) the variability in macroinvertebrate assemblages at seven spatial scales; and (2) the change in taxon richness with increasing sampling effort. An analysis of variance (ANOVA) model calculated spatial variance components for taxon richness, total density, percent individuals of Ephemeroptera, Plecoptera and Trichoptera (EPT), percent dominance and Shannon diversity.
2. At the landscape level, ecoregion and among‐streams components dominated variance for most metrics, accounting for 43–72% of total variance. However, ecoregion accounted for very little variance in total density and 36% of the variance was attributable to differences between streams. For other metrics, variance components were more evenly divided between stream and ecoregion effects.
3. Within streams, approximately 70% of variance was associated with unstructured local spatial variation and not associated with habitat type or transect position. The remaining variance was typically split about evenly between habitat and transect. Sample position within a transect (left, centre or right) accounted for virtually none of the variance for any metric.
4. New taxa per stream increased rapidly with sampling effort with the first four to eight Surber samples (500–1000 individuals counted), then increased more gradually. After counting more than 50 samples, new taxa continued to be added in stream reaches that were 80 times as long as their mean wetted width. Thus taxon richness was highly dependent on sampling effort, and comparisons between sites or streams must be normalized for sampling effort.
5. Characterization of spatial variance structure is fundamental to designing sampling programmes where spatial comparisons range from local to regional scales. Differences in metric responses across spatial scales demonstrate the importance of designing sampling strategies and analyses capable of discerning differences at the scale of interest.     

Effects of sand sedimentation on the macroinvertebrate fauna of lowland streams: are the effects consistent?

1. In lowland streams sand sedimentation can produce sand slugs: very slow moving, discrete volumes of sand that are created episodically. Hypothetically, such sedimentation causes losses of habitat and fauna but little is known about the effects of sand slugs. In south‐eastern Australia sand slugs are widespread, especially in streams with granitic catchments. 2. This study in north‐central Victoria was centred on three streams that rise in the Strathbogie Ranges and flow out onto lowland plains, where they contain sand slugs. Below the sand slugs, the streams are slow‐flowing ‘chains of ponds’ with a clay streambed. To correct for potential upstream‐downstream confounding of comparisons, two unsanded, nearby streams were included as potential controls. Habitat measurements and faunal samples were taken in Spring 1998, from three sites in the sand slug and three sites in the clay‐bed, downstream sections of each impacted stream, as well as from three sites in commensurate upstream and downstream sections of the control streams. 3. The sand‐slugged sections had significantly higher velocities, shallower depths and less coarse woody debris than the unsanded downstream sections. Macroinvertebrate taxon richness and abundance showed some significant differences between the sand and clay sections compared with commensurate up‐ and downstream locations in the control streams. Effects were not uniform, however. In Castle Creek there were no significant differences between the sand and clay sections, in Pranjip‐Ninemile Creek taxon richness and abundances were higher in sand than in the clay sections, whereas in Creightons Creek the ‘expected’ results of lower taxon richness and abundance in the sand were found. 4. Of the 40 most common taxa, only eight provided a clear signal related to sand and, of these, one (Slavina sp.) occurred only in the sand slugs, whereas the other seven had significantly higher numbers in the clay sections. Of these taxa, three were ostracods, three were chironomids and one was a tubificid oligochaete, all taxa that live in detritus‐rich environments. Overall faunal composition did not show a clear distinction though, between sandy and clay sites. The sand slug community of Creightons Creek was very different from the other communities in all of the streams. There were clear differences in community composition between the sand‐affected and the control streams, even for downstream, clay sections, suggesting they cannot act as controls for the impacted sections of the sand‐slugged streams. 5. Differences between streams within categories (particularly between sand‐slugged streams) and between sites in the same section of stream accounted for most of the variability in species richness and the abundances of each of the 40 most common taxa. That finding was repeated when data were examined at the family level, for both numbers of families per sample and collated lists of families occurring across sites. These results strongly suggest that the effects of sedimentation by sand slugs do not overwhelm background variation in macroinvertebrate density and diversity. Overall the results suggest that many taxa may respond individually, and that there is much variation between sand‐affected streams even over relatively small (approximately <10 km) spatial scales.     

Stream macroinvertebrate assemblage uniformity and drivers in a tropical bioregion

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Fish richness and species-habitat relationships in two coastal streams of French Guiana, South America

We examined the factors controlling fish species richness and taxa-habitat relationships in the Malmanoury and Karouabo coastal streams in French Guiana between the short and long rainy seasons. The aims were to evaluate the environmental factors that describe species richness on different scales and to define the ecological requirements of fish taxa in the two streams at that period of the year. We sampled ten regularly spaced freshwater sites in each stream with rotenone. We caught a total of 7725 individuals representing 52 taxa from 21 families and 6 orders. More taxa were caught in the Malmanoury (n=46) than in the Karouabo stream (n=37). These values augmented by the number of fish taxa caught only by gill nets in a parallel survey fitted very well to a log-log model of fish richness versus catchment area in Guianese rivers. Most of the fish taxa encountered in the Malmanoury and Karouabo streams were of freshwater origin and nearly all the fish species caught in these two small coastal streams were also found in the nearby Sinnamary River with the exceptions of the cichlid Heros severus and the characid Crenuchus spirulus. Moreover, no significant relationship was found between a size-independent estimate of fish richness and distance from the Ocean. Thus, despite their coastal position, the Malmanoury and Karouabo streams contained fish assemblages with strong continental affinities. At a local scale, independently of site size, those with relatively more habitat types harbored a relatively greater number of fish taxa. Canopy cover, water conductivity and bank length were the most important environmental variables for fish assemblage composition at that period of the year. Oxygen and vegetation participated also in defining fish habitat requirements but to a lesser extent. This revised version was published online in July 2006 with corrections to the Cover Date.     

Seasonal dynamics of macroinvertebrate assemblages in the benthos and associated with detritus packs in two low-order streams with different riparian vegetation

• 1 The seasonal dynamics of the benthic macroinvertebrate assemblage, and the subset of this assemblage colonising naturally formed detritus accumulations, was investigated in two streams in south‐west Ireland, one draining a conifer plantation (Streamhill West) and the other with deciduous riparian vegetation (Glenfinish). The streams differed in the quantity, quality and diversity of allochthonous detritus and in hydrochemistry, the conifer stream being more acid at high discharge. We expected the macroinvertebrate assemblage colonising detritus to differ in the two streams, due to differences in the diversity and quantity of detrital inputs.
• 2 Benthic density and taxon richness did not differ between the two streams, but the density of shredders was greater in the conifer stream, where there was a greater mass of benthic detritus. There was a significant positive correlation between shredder density and detritus biomass in both streams over the study period.
• 3 Detritus packs in the deciduous stream were colonised by a greater number of macroinvertebrates and taxa than in the conifer stream, but packs in both streams had a similar abundance of shredders. The relative abundance of taxa colonising detritus packs was almost always significantly different to that found in the source pool of the benthos.
• 4 Correspondence analysis illustrated that there were distinct faunal differences between the two streams overall and seasonally within each stream. Differences between the streams were related to species tolerances to acid episodes in the conifer stream. Canonical correspondence analysis demonstrated a distinct seasonal pattern in the detrital composition of the packs and a corresponding seasonal pattern in the structure of the detritus pack macroinvertebrate assemblage.
• 5 Within‐stream seasonal variation both in benthic and detritus pack assemblages and in detrital inputs was of similar magnitude to the between‐stream variation. The conifer stream received less and poorer quality detritus than the deciduous stream, yet it retained more detritus and had more shredders in the benthos. This apparent contradiction may be explained by the influence of hydrochemistry (during spate events) on the shredder assemblage, by differences in riparian vegetation between the two streams, and possibly by the ability of some taxa to exhibit more generalist feeding habits and thus supplement their diets in the absence of high quality detritus.