Macroinvertebrate diversity in headwater streams: a review

1. Headwater streams are ubiquitous in the landscape and are important sources of water, sediments and biota for downstream reaches. They are critical sites for organic matter processing and nutrient cycling, and may be vital for maintaining the 'health' of whole river networks.
2. Macroinvertebrates are an important component of biodiversity in stream ecosystems and studies of macroinvertebrate diversity in headwater streams have mostly viewed stream systems as linear reaches rather than as networks, although the latter may be more appropriate to the study of diversity patterns in headwater systems.
3. Studies of macroinvertebrate diversity in headwater streams from around the world illustrated that taxonomic richness is highly variable among continents and regions, and studies addressing longitudinal changes in taxonomic richness of macroinvertebrates generally found highest richness in mid-order streams.
4. When stream systems are viewed as networks at the landscape-scale, α-diversity may be low in individual headwater streams but high β-diversity among headwater streams within catchments and among catchments may generate high γ-diversity.
5. Differing ability and opportunity for dispersal of macroinvertebrates, great physical habitat heterogeneity in headwater streams, and a wide range in local environmental conditions may all contribute to high β-diversity among headwater streams both within and among catchments.
6. Moving beyond linear conceptual models of stream ecosystems to consider the role that spatial structure of river networks might play in determining diversity patterns at the landscape scale is a promising avenue for future research.     

Effects of snow cover on the benthic fauna in a glacier-fed stream

1. Alpine streams above the tree line are covered by snow for 6–9 months a year. However, winter dynamics in these streams are poorly known. The annual patterns of macroinvertebrate assemblages were studied in a glacial stream in the Austrian Alps, providing information on conditions under the snow.
2. Snow cover influenced water temperature, the content of benthic organic matter and insect development. Taxa richness and abundance of macroinvertebrates did not show a pronounced seasonal pattern. The duration of the autumn period with stable stream beds was important in determining the abundance and composition of the winter fauna.
3. There were significant differences in species composition between summer and winter. Two potential strategies in larval survival were evident: adaptation to the extreme abiotic conditions in summer (e.g. Diamesa spp.) or avoidance of these conditions and development during winter (e.g. Ephemeroptera and Plecoptera).
4. A comparison of a stream reach with continuous snow cover and a stream reach that remained open throughout winter showed that conditions under snow are suboptimal. At the open stream site, with higher water temperatures and greater food supply (benthic organic matter content), abundance and taxa richness was higher and larval growth was faster. Several taxa were found exclusively at this site.
5. Winter conditions did not provide an entirely homogeneous environment, abiotic conditions changed rapidly, especially at the onset of snowfall and at snowmelt. Continuous monitoring is necessary to recognize spatial and temporal heterogeneity in winter environments and the fauna of alpine streams.     

Flight activity of adult stoneflies in relation to weather

Abstract. 1. Dispersal of adult aquatic insects between streams may have important consequences for local and regional population dynamics, but little is known about how dispersal is affected by weather conditions.
2. The influence of meteorological variables on flight activity of adult stoneflies (Plecoptera: Leuctridae, Nemouridae, and Chloroperlidae) was investigated using Malaise traps adjacent to three upland streams in the Plynlimon area of mid Wales, U.K.
3. Numbers of adult stoneflies captured weekly in the traps were related positively to air temperature and related negatively to wind speed. Meteorological conditions during daylight showed stronger relationships with flight activity than did conditions at night.
4. There was inter-site variation in the strength of weather effects on stonefly flight. Wind speed was significant at only one site, which had higher average wind speed than the other sites.
5. Annual variation in weather conditions during adult flight periods may result in varying extent of dispersal between sites, influencing community dynamics over a wide area.     

Response of aquatic hyphomycete communities to enhanced stream retention in areas impacted by commercial forestry

1. Aquatic hyphomycetes are an important component of detritus processing in streams. Their response to enhanced stream retentiveness was tested by manipulating three streams located in Kielder Forest (northern England), a large plantation of exotic conifers, and two streams in Montagne Noire (south-west France) dominated by native broadleaf woodland. Treatment was by placement of logs or plastic litter traps into a 10–20 m stream section. Fungal spores were collected from stream water upstream and downstream of the treated sections over 1–2 years.
2. The average concentration of fungal spores in reference sections was nearly 10× greater in the French streams than in the English streams. The number of hyphomycete species was also higher in the French streams. These differences between regions were probably a consequence of the much lower standing stock and diversity of leaf litter in the English streams.
3. Despite these large regional differences, the treatment had a clear effect in all streams. Detrital standing stocks were enhanced in treated sections by up to 90% in French streams and 70% in English streams.
4. Mean spore density below treated sections increased by 1.8–14.8% in French streams and 10.2–28.9% in the naturally less retentive English streams. The number of fungal species increased significantly below the treated sections of the English streams, although not the French ones.
5. In biologically impoverished plantation streams, input of woody debris can increase detritus retention and enhance hyphomycete diversity and productivity. This may have consequent benefits for detritus processing and macroinvertebrate production.     

Distributions of Ephemeroptera, Plecoptera, and Trichoptera of three maritime catchments differing in pH

1. Two broad-scale environmental influences affecting species of Ephemeroptera, Trichoptera and Plecoptera inhabiting riffle habitat of three study catchments in New Brunswick and Nova Scotia were stream size-temperature-related variables and acidity-related variables. 2. Species richness was most affected by acidity in tributaries of intermediate size <0.001<0.1m³s^?1). 3. Of the three insect orders investigated, mayfly species richness was affected most by acidity, and stonefly species richness affected least by this factor. 4. Zoogeographical isolation of the Nova Scotian catchments resulted in absence of some species of low general abundance, but these species had little influence on the site classification by TWINSPAN analysis. 5. Predaceous stoneflies were collected in greater numbers from circumneutral sites and predaceous caddisflies in greater numbers from the Nova Scotian sites. 6. Although the Nova Scotian catchments have probably been historically acidic, due to high concentrations of organic acids, pH currently limits the distributions of many indigenous invertebrate species. These species may be vulnerable to the more recent, additional, anthropogenic acidification of these catchments.     

Distribution Patterns,Species Assemblages and Habitat Selection of the Stoneflies (Plecoptera) from Two Mediterranean River Basins in Southern Spain

The stonefly distribution and its relationship with habitat changes, based on stream physico chemical features, were investigated in two Mediterranean river basins (Guadaira and Guadalete, S Spain). Plecopteran nymph distribution varied along an elevation gradient. Both stonefly species richness and species diversity increased with altitude. Stoneflies were able to tolerate a wide range of environmental conditions but were absent from low altitude sites, temporary streams with high salinity values and high water temperature. A total of 13 stonefly species were found in the study area, from which Tyrrhenoleuctra minuta (Klapálek ) and Protonemura sp. were dominant. The most widespread species were Nemoura lacustris and Capnioneura mitis. Three distinct species assemblages were observed according to their distribution patterns, but with similar environmental preferences. Capnioneura petitpierreae and T. minuta showed preferences to low altitude sites, whereas C. mitis and N. lacustris were found throughout all sites. T. minuta and N. lacustris inhabited permanent and temporary sites, while the same species and C. mitis also were found in semipermanent streams. Temporally, most stoneflies were caught during winter (85.9%), especially at the low altitude sites.     

Ohio USA stoneflies (Insecta, Plecoptera): species richness estimation, distribution of functional niche traits, drainage affiliations, and relationships to other states

Ohio is an eastern USA state that historically was >70% covered in upland and mixed coniferous forest; about 60% of it glaciated by the Wisconsinan glacial episode. Its stonefly fauna has been studied in piecemeal fashion until now. The assemblage of Ohio stoneflies was assessed from over 4,000 records accumulated from 18 institutions, new collections, and trusted literature sources. Species richness totaled 102 with estimators Chao2 and ICE Mean predicting 105.6 and 106.4, respectively. Singletons and doubletons totaled 18 species. All North American families were represented with Perlidae accounted for the highest number of species at 34. The family Peltoperlidae contributed a single species. Most species had univoltine-fast life cycles with the vast majority emerging in summer, although there was a significant component of winter stoneflies. Nine United States Geological Survey hierarchical drainage units level 6 (HUC6) were used to stratify specimen data. Species richness was significantly related to the number of unique HUC6 locations, but there was no relationship with HUC6 drainage area. A nonparametric multidimensional scaling analysis found that larger HUC6s in the western part of the state had similar assemblages with lower species richness that were found to align with more savanna and wetland habitat. Other drainages having richer assemblages were aligned with upland deciduous and mixed coniferous forests of the east and south where slopes were higher. The Ohio assemblage was most similar to the well-studied fauna of Indiana (88 spp.) and Kentucky (108 spp.), two neighboring states. Many rare species and several high quality stream reaches should be considered for greater protection.     

Patterns of species richness for blackflies (Diptera: Simuliidae) in the Nearctic and Neotropical regions

Abstract.  1. Patterns of simuliid species richness were examined over a variety of scales at 532 stream sites in the Nearctic (394) and Neotropical (138) regions. In Nearctic streams, species richness of immature blackflies both within and across ecoregions and over two seasons was examined. Stream variables at each site included seston, width, depth, velocity, discharge, conductivity, pH, dissolved oxygen, water temperature, dominant streambed-particle size, canopy cover, and riparian vegetation. These variables were subjected to a principal component analysis and derived principal components were related back to richness, using regression analysis. At the level of the stream reach, richness was not highly correlated with single-point measurements of stream conditions.
2. Using data from both Nearctic and Neotropical sites, the effect of regional richness on local richness was examined. As regional richness increased, local diversity reached an asymptote in which further increases in regional richness were not matched by increases in local richness. Hence, simuliid communities are best described as saturated (type II) communities, consistent with the current view of lotic communities as non-equilibrium systems.
3. The well-established pattern of greater species richness in tropical regions was not observed in this study. To the contrary, blackfly richness is higher in temperate streams than in tropical streams at both local and regional scales.     

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.     

Disruption of a longitudinal pattern in environmental factors and benthic fauna by a glacial tributary

SUMMARY 1. In the upper Rhône catchment (Swiss Alps), modifications in the longitudinal pattern of environmental conditions and the benthic macroinvertebrate fauna were investigated in a glacier-fed stream (Rhône) at its confluence with a smaller glacier-fed tributary (Mutt) in June, August and September 1998. The distance to the source glacier was greater for the Mutt than for the Rhône.
2. Environmental conditions were harsher for the biota in the main stream upstream of the confluence than in the tributary. The tributary upstream of the confluence was characterised by higher taxonomic richness and abundance of the zoobenthos than the Rhône upstream.
3. Although environmental conditions in the main stream were little modified by the tributary, the fauna was richer and more diverse below the confluence. During the period of ice melt, colonisation from the Mutt led to the occurrence of faunal elements atypical of glacial streams in the main glacial stream upstream of the confluence, where water temperature remains below 4 °C.
4. Although contributing an average of only 10% to the Rhône discharge, the Mutt tributary is suggested to be the faunal driver of the system.     

Salamander occupancy in headwater stream networks

1. Stream ecosystems exhibit a highly consistent dendritic geometry in which linear habitat units intersect to create a hierarchical network of connected branches.
2. Ecological and life history traits of species living in streams, such as the potential for overland movement, may interact with this architecture to shape patterns of occupancy and response to disturbance. Specifically, large-scale habitat alteration that fragments stream networks and reduces connectivity may reduce the probability a stream is occupied by sensitive species, such as stream salamanders.
3. We collected habitat occupancy data on four species of stream salamanders in first-order (i.e. headwater) streams in undeveloped and urbanised regions of the eastern U.S.A. We then used an information–theoretic approach to test alternative models of salamander occupancy based on a priori predictions of the effects of network configuration, region and salamander life history.
4. Across all four species, we found that streams connected to other first-order streams had higher occupancy than those flowing directly into larger streams and rivers. For three of the four species, occupancy was lower in the urbanised region than in the undeveloped region.
5. These results demonstrate that the spatial configuration of stream networks within protected areas affects the occurrences of stream salamander species. We strongly encourage preservation of network connections between first-order streams in conservation planning and management decisions that may affect stream species.     

Community structure in some southern English streams: the influence of species interactions

SUMMARY. 1. The results of a survey of thirty-four stream sites, differing in pH and invertebrate species richness, indicated that the pool of locally available, suitably adapted species was smaller in the acid streams. This plays a part in determining the general pattern of lower species richness at more acid sites.
2. Diversity of feeding categories increased with species richness, indicating that a greater range of food resources was available in the less acid, more species-rich communities.
3. The pattern of predation varied with pH and species richness. The numbers of large insect predators were lower in the less acid, more species-rich communities and this was correlated with the presence of fish.
4. A detailed study of the guild of detritivorous stoneflies in four streams differing in species richness provided evidence that density compensation occurs, niche width decreases and niche overlap declines as species richness increases.
5. We discuss the roles that competition and predation play in determining the structure and richness of stream invertebrate communities.     

Stream channel geomorphology influences mussel abundance in southern Appalachian streams, U.S.A.

1. Studies of North American streams have shown that hydraulic parameters and stream geomorphology can explain unionid mussel abundance at both the reach and catchment scale. However, few studies have examined applicability of hydrogeomorphic variables across broader spatial scales, such as across whole catchments, or have elucidated conditions under which spates can affect mussel populations in streams. 2. We quantified freshwater mussel abundance and species richness and their physical habitat at 24 sites in eight streams in southern Appalachian catchments in 2000 and 2001. In addition, we modelled site‐specific hydraulic parameters during summer baseflow and bankfull stages to estimate high‐ and low‐discharge conditions, respectively. 3. Mussel abundance was related to stream geomorphology, whereas richness was related to stream size. Baseflow habitat parameters explained only minor variation in abundance or richness, and both measures were highly correlated with mean current velocity or stream size. Bankfull shear stress composed a relatively low proportion of overall mussel habitat variability, but it accounted for significant variation in abundance and richness. 4. Mussel abundance was highly variable at sites subject to low‐shear stress during spates, whereas abundance always was low at sites subject to high‐shear stress. These data suggest that habitat conditions during floods, rather than those at summer baseflow, limit the abundance of mussels in Appalachian streams. These data also suggest that mussel abundance and assemblage structure may be sensitive to any changes in channel geomorphology and hydraulic conditions that might result from land use in the catchment.     

Evaluation of methods for estimating macroinvertebrate species richness using individual stones in tropical streams

1. The most straightforward way to assess diversity in a site is the species count. However, a relatively large sample is needed for a reliable result because of the presence of many rare species in rich assemblages. The use of richness estimation methods is suggested by many authors as a solution for this problem in many cases.
2. We examined the performance of 13 methods for estimating richness of stream macroinvertebrates inhabiting riffles both at local (stream) and regional (catchment) scales. The evaluation was based on (1) the smallest sub-sample size needed to estimate total richness in the sample, (2) constancy of this size, (3) lack of erratic behaviour in curve shape and (4) similarity in curve shape through different data sets. Samples were from three single stream sites (local) and three from several streams within the same catchment basin (regional). All collections were made from protected forest areas in south-east Brazil.
3. All estimation methods were dependent on sub-sample size, producing higher estimates when using larger sub-sample sizes. The Stout and Vandermeer method estimated total richness in the samples with the smallest sub-sample size, but showed some erratic behaviour at small sub-sample sizes, and the estimated curves were not similar among the six samples. The Bootstrap method was the best estimator in relation to constancy of sub-sample sizes, but needed an unacceptably large sub-sample to estimate total richness in the samples. The second order Jackknife method was the second best estimator both for minimum sub-sample size and constancy of this size and we suggest its use in future studies of diversity in tropical streams. Despite the inferior performance of several other methods, some produced acceptable results. Comments are made on the utility of using these estimators for predicting species richness in an area and for comparative purposes in diversity studies.     

Mayflies,stoneflies, and caddisflies of streams and marshes of Indiana Dunes National Lakeshore,USA

United States National Parks have protected natural communities for one hundred years. Indiana Dunes National Lakeshore (INDU) is a park unit along the southern boundary of Lake Michigan in Indiana, USA. An inventory of 19 sites, consisting of a seep, 12 streams, four marshes, a bog, and a fen were examined for mayflies (Ephemeroptera), stoneflies (Plecoptera), and caddisflies (Trichoptera) (EPT taxa). Volunteers and authors collect 35 ultraviolet light traps during summer 2013 and supplementary benthic and adult sampling added species not attracted by lights or that were only present in colder months. Seventy-eight EPT species were recovered: 12 mayflies, two stoneflies, and 64 caddisflies. The EPT richness found at INDU was a low proportion of the number of species known from Indiana: caddisflies contributed only 32.7% of known state fauna, mayflies and stoneflies contributed 8.4% and 2.3%, respectively. Site EPT richness ranged from one for a seep to 34 for an 8 m-wide stream. Richness in streams generally increased with stream size. Seven new state records and rare species are reported. The number of EPT species at INDU is slightly larger than that found at Isle Royale National Park in 2013, and the community composition and evenness between orders were different.     

Species richness and spatial distribution of blackflies (Diptera: Simuliidae) in streams of Central Amazonia, Brazil

1. The spatial distribution and species richness of blackflies were evaluated at 58 stream sites in Central Amazonia, Brazil. Samples were taken along a north–south axis of approximately 130 km and a east–west axis of approximately 220 km.
2. Based on stream-site characteristics, the occurrence of larvae of the six most frequently collected species was highly predictable (79.3–91.5% accuracy in prediction of occurrence). The predictive value of stream size and the presence of impoundments agrees with results of similar work in the Holarctic Region, suggesting a general responses of blackflies to environmental parameters.
3. Although only 19.0% of interstream variation in species richness was explained by a regression model, results suggested that species richness was greater in larger, cooler, faster, covered streams with rocky beds than in smaller, warmer, slower, open streams with sandy bottoms. Overall, the species richness of blackflies (11 species in total) was lower than in the temperate zone suggesting, for some taxa at least, that aquatic communities do not follow the terrestrial pattern of greater species richness in the tropics.     

Diet and predation by three leaf-associated stoneflies (Plecoptera) in an Arkansas mountain stream

SUMMARY. 1. Life cycles, food habits, mouthpart morphologies, prey preferences, and predator-prey size relationships were investigated for the three most common stoneflies in leaf packs in the Little Missouri River, Arkansas: Clioperla clio (Newman), Isoperla namata Prison, and Perlesta spp. Each species was univoltine and had a fast seasonal cycle, with extended egg or nymphal diapause, rapid nymphal growth and emergence in spring to early summer.
2. Foregut analysis showed predictable dietary shifts by C. clio and Perlesta spp., from detritus and diatoms in early instars to invertebrate prey in later instars. Isoperla namata fed facultatively on insects, detritus and diatoms, with no conspicuous ontogenetic shifts. The mouthparts of all three species strongly reflected their diet.
3. Electivity analysis indicated opportunistic feeding by the three species, with feeding rarely differing significantly from random.
4. Sizes of stonefly predators and their ingested prey were highly correlated ( P <0.01). However, rather than shifting toward larger prey sizes, growing predators expanded their size thresholds and continued to include numerous small prey items in their diet. Prey choice was governed most directly by prey availability, because stoneflies selected the most abundant groups, irrespective of size or taxon.
5. The likelihood of competition among the three stoneflies for prey was minimized by timing of their life cycles, differential food use and probably the temporary nature of leaf pack habitats.     

Forest proportion as indicator of ecological integrity in streams using Plecoptera as a proxy

An assessment system suitable to support implementation of the EU Water Framework Directive's local water management plans should build on quantitative knowledge about a suite of well-documented indicator and umbrella species’ requirements for different stream orders. Assuring high communication value for improving local public awareness and participation for restoring ecological integrity in impaired headwater streams is critical. Loss and fragmentation of forests are major threats to ecological integrity. The aquatic macroinvertebrate order Plecoptera is commonly used as an indicator of the ecological integrity of streams. We measured abundance and taxonomic richness of Plecoptera in relation to land cover and water chemistry in second and third order catchments’ in 25 headwater streams in Central Europe's Carpathian Mountains. Plecoptera abundance and Plecoptera taxa richness were positively correlated to each other, as well as to forest proportion in the catchments, but negatively correlated to catchment area, inorganic carbon, alkalinity and conductivity. Segmented linear regression was then used to identify thresholds associated to forest proportion as a surrogate for catchment integrity. No threshold was found for Plecoptera abundance, but for taxa richness a threshold of 54% forest cover was found, below which Plecoptera was affected in second order streams. Using Plecoptera as a proxy for ecological integrity this study indicates that forest cover is an effective bioindicator in headwater catchments for predicting the ecological status of headwater streams. The non-linear relationship between forest cover and Plecoptera can be used as a science-based norm whereby land cover monitoring can be used to assess the ecological status of streams.     

Stable isotopes identify dispersal patterns of stonefly populations living along stream corridors

1. Populations in different locations can exchange individuals depending on the distribution and connectivity of suitable habitat, and the dispersal capabilities and behaviour of the organisms. We used an isotopic tracer, ¹⁵N, to label stoneflies (Leuctra ferruginea) to determine the extent of adult flight along stream corridors and between streams where their larvae live. 2. In four mass, mark‐capture experiments we added ¹⁵NH₄Cl continuously for several weeks to label specific regions of streams within the Hubbard Brook Experimental Forest, NH, U.S.A. We collected adult stoneflies along the labelled streams (up to 1.5 km of stream length), on transects through the forest away from labelled sections (up to 500 m), and along an 800‐m reach of adjacent tributary that flows into a labelled stream. 3. Of 966 individual adult stoneflies collected and analysed for ¹⁵N, 20% were labelled. Most labelled stoneflies were captured along stream corridors and had flown upstream a mean distance of 211 m; the net movement of the population (upstream + downstream) estimated from the midpoint of the labelled sections was 126 m upstream. The furthest male and female travelled approximately 730 m and approximately 663 m upstream, respectively. We also captured labelled mature females along an unlabelled tributary and along a forest transect 500 m from the labelled stream, thus demonstrating cross‐watershed dispersal. 4. We conclude that the adjacent forest was not a barrier to dispersal between catchments, and adult dispersal linked stonefly populations among streams across a landscape within one generation. Our data on the extent of adult dispersal provide a basis for a conceptual model identifying the boundaries of these populations, whose larvae are restricted to stream channels, and whose females must return to streams to oviposit.     

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.