Resistance and resilience of stream insect communities to repeated hydrologic disturbances after a wildfire

1. Wildfires are often followed by severe, sediment‐laden floods in burned catchments. In this study, we documented resistance and resilience of stream insect communities to repeated postfire flash floods in a ‘burned stream’. We employed a before‐after‐control‐impact (BACI) design, where communities in comparable reaches of a burned stream and a reference stream were sampled from 2 years before, to 6 years after, a crown wildfire in north‐central New Mexico. 2. The first 100‐year flood following the 1996 Dome wildfire reduced total insect density and taxon richness to near zero in the burned stream. Despite showing low resistance, density returned rapidly to prefire levels because of colonisation by simuliids, chironomids and the mayfly Baetis tricaudatus. In general, taxa that were generalist feeders (collectors) with strong larval dispersal dominated communities in early postfire years with repeated, moderate flash floods. 3. Taxon richness and community composition were less resilient to postfire hydrologic disturbances. Taxon richness did not recover until floods dampened 4 years after the fire. Despite hydrologic recovery, composition in the burned stream still differed from prefire and reference stream compositions after 6 years postfire. A unique assemblage, dominated by taxa with strong larval or adult dispersal, was established after flash floods abated. Specialist feeders (shredders and grazers) that were common in prefire years were reduced or absent in the postfire assemblage. 4. Community succession in the burned stream was explained by the interaction between species traits, geographic barriers to colonisation and hydrologic conditions after the fire. Comparable changes in insect density, taxon richness, community composition and trait representation were not found in the reference stream, providing strong evidence that repeated postfire flash floods shaped community responses in the burned stream.     

Fire and regeneration: the role of seed banks in the dynamics of northern heathlands

Questions: How do species composition and abundance of soil seed bank and standing vegetation vary over the course of a post‐fire succession in northern heathlands? What is the role of seed banks – do they act as a refuge for early successional species or can they simply be seen as a spillover from the extant local vegetation? Location: Coastal Calluna heathlands, Western Norway. Methods: We analysed vegetation and seed bank along a 24‐year post‐fire chronosequence. Patterns in community composition, similarity and abundances were tested using multivariate analyses, Sørensen's index of similarity, vegetation cover (%) and seedling counts. Results: The total diversity of vegetation and seed bank were 60 and 54 vascular plant taxa, respectively, with 39 shared species, resulting in 68% similarity overall. Over 24 years, the heathland community progressed from open newly burned ground via species rich graminoid‐ and herb‐dominated vegetation to mature Calluna heath. Post‐fire succession was not reflected in the seed bank. The 10 most abundant species constituted 98% of the germinated seeds. The most abundant were Calluna vulgaris (49%; 12 018 seeds m^?2) and Erica tetralix (34%; 8 414 seeds m^?2). Calluna showed significantly higher germination the first 2 years following fire. Conclusions: Vegetation species richness, ranging from 23 to 46 species yr^?1, showed a unimodal pattern over the post‐fire succession. In contrast, the seed bank species richness, ranging from 21 to 31 species yr^?1, showed no trend. This suggests that the seed bank act as a refuge; providing a constant source of recruits for species that colonise newly burned areas. The traditional management regime has not depleted or destroyed the seed banks and continued management is needed to ensure sustainability of northern heathlands.     

Longitudinal and seasonal distribution patterns of the benthic fauna of an alpine glacial stream (Val Roseg, Swiss Alps)

1. Seasonal changes in longitudinal patterns of environmental conditions and macroinvertebrate community distributions were examined in an alpine glacial stream (Roseg River, Switzerland). 2. Physico‐chemical parameters reflected seasonal changes in glacial influence via shifts in water sources and flowpaths (glacial meltwater versus ground water), and were best described by turbidity, particulate phosphorus and specific conductance. High nitrogen concentrations indicated snowmelt was the main water source in June. 3. Macroinvertebrate densities and taxon richness were highest during spring (4526 m^–2 and 16 taxa, all sites combined) and late autumn/early winter (8676–13 398 m^–2 with 16–18 taxa), indicating these periods may be more favourable for these animals than summer when glacial melting is maximal. Diamesa spp. (Chironomidae) dominated the fauna at the upper three sites (>95% of zoobenthos) and were abundant at all locations. Other common taxa at lower sites (1.2–10.6 km downstream of the glacier terminus) included other chironomids (Orthocladiinae, Tanytarsini), the mayflies Baetis alpinus and Rhithrogena spp., the stoneflies Leuctra spp. and Protonemura spp., blackflies (Simulium spp., Prosimulium spp.), and Oligochaeta. 4. Co‐inertia analysis revealed a strong relationship between environmental conditions and benthic macroinvertebrate assemblages. Furthermore, it elucidated temporal variability in longitudinal response patterns, as well as a similarity in temporal patterns among individual sites. 5. Our results suggest that zoobenthic gradients are not solely related to temperature and channel stability. Seasonal shifts in sources and pathways of water (i.e. extent of glacial influence), and periods of favourable environmental conditions (in spring and late autumn/early winter) also strongly influenced zoobenthic distributions.     

Benthic secondary production and biomass of insects emerging from a northern German temperate stream

• 1 Secondary production and emergence of aquatic insects were examined in the outlet of Lake Belau, Northern Germany, by means of benthic samples and emergence traps.
• 2 At three stream sections annual larval secondary production varied between 4.9 and 10.8 gDM (dry mass) m^‐2 year^‐1. Insects contributed with 3.4, 8.9, and 8.7% to the total macroinvertebrate production that varied between 56.5 and 215.1 gDM m^‐2 year^‐1. Emerged biomass was between 1.0 and 2.0 gDM m^‐2 year^‐1. At all three stream sections Diptera dominated with a larval production of 3.0–l6.1 gDM m^‐2 year^‐1, followed by Trichoptera with 1.0–2.1 and Ephemeroptera with up to 0.9 gDM m^‐2 year^‐1.
• 3 Average larval production amounted to 9.0 gDM m^‐2 year^‐1 and emerged biomass to 1.7 gDM m^‐2 year^‐1. Larvae of insects amounted to 7.0% of total macroinvertebrate production.
• 4 The ratio of annual emerged biomass to secondary production (E/P) varied among individual taxa. At the stream sections the ratio ranged from 15.9% to 20.1% with an average of 18.3% for the stream.
• 5 Relative constancy of the E/P ratio suggests that the determination of emerged biomass can be used as a method for estimating the secondary production of aquatic insects. The composition of functional feeding groups clearly differs between emerged biomass and total macroinvertebrate production. Therefore, the method does not allow conclusions on the level of production of the whole benthic community. However, composition of functional feeding groups at emergence roughly reflects composition of these groups in the benthic insect community.

     

Effects of natural disturbance on stream communities: a habitat template analysis of arctic headwater streams

1. We used the habitat template approach to test the hypothesis that substratum stability, freezing and nutrient supply were determinants of community structure in 19 headwater streams of arctic Alaska. Streams were selected from five categories: glacier (n = 3), mountain (4), mountain spring (4), tundra spring (4) and tundra (4). 2. Bed movement among streams ranged from 0 to 97% during a ～2‐month summer season. Glacier and mountain streams had significantly higher bed movement than tundra and spring streams (P < 0.001). 3. All glacier and tundra streams froze solid during winter; all mountain spring streams remained unfrozen. Freezing among mountain and tundra spring streams was variable, with a subset of streams flowing throughout winter. 4. With the exception of glacier streams, which showed high concentrations of NH₄⁺ and NO₃^? (P < 0.001), differences in nutrient concentrations among stream types were not significant. 5. Algal taxon richness was greatest in tundra springs (13 taxa) and lowest in glacier streams (five taxa, P < 0.001), as was algal biovolume (7350 versus 687 mm³ m^?2, P < 0.001). Macroinvertebrate taxon richness was lower in glacier streams (4.7 ± 1.7, P < 0.005) than the other stream types (20.5–25.0 taxa), and biomass was greater in mountain springs (4837 mg m^?2) and tundra springs (3367 mg m^?2, P < 0.001). 6. Multidimensional scaling and multiple regression analyses of macroinvertebrate (biomass) and periphyton (biovolume) indicated that a 2‐dimensional habitat template with bed movement and freezing as axes provides an accurate model of major factors controlling the community structure of headwater streams in arctic Alaska.     

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

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Invertebrate assemblages of pools in arid‐land streams have high functional redundancy and are resistant to severe drying

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Food web structure and function in two arctic streams with contrasting disturbance regimes

1. We studied the effect of substratum movement on the communities of adjacent mountain and spring tributaries of the Ivishak River in arctic Alaska (69°1′N, 147°43′W). We expected the mountain stream to have significant bed movement during summer because of storm flows and the spring stream to have negligible bed movement because of constant discharge. 2. We predicted that the mountain stream would be inhabited only by taxa able to cope with frequent bed movement. Therefore, we anticipated that the mountain stream would have lower macroinvertebrate species richness and biomass and a food web with fewer trophic levels and lower connectance than the spring stream. 3. Substrata marked in situ indicated that 57–66% of the bed moved during summer in the mountain stream and 4–20% moved in the spring stream. 4. Macroinvertebrate taxon richness was greater in the spring (25 taxa) than in the mountain stream (20 taxa). Mean macroinvertebrate biomass was also greater in the spring (4617 mg dry mass m^?2) than in the mountain stream (635 mg dry mass m^?2). Predators contributed 25% to this biomass in the spring stream, but only 7% in the mountain stream. 5. Bryophyte biomass was >1000 times greater in the spring stream (88.4 g ash‐free dry mass m^?2) than the mountain stream (0.08 g ash‐free dry mass m^?2). We attributed this to differences in substratum stability between streams. The difference in extent of bryophyte cover between streams probably explains the high macroinvertebrate biomass in the spring stream. 6. Mean food‐web connectance was similar between streams, ranging from 0.18 in the spring stream to 0.20 in the mountain stream. Mean food chain length was 3.04 in the spring stream and 1.83 in the mountain stream. Dolly Varden char (Salvelinus malma) was the top predator in the mountain stream and the American dipper (Cinclus mexicanus) was the top predator in the spring stream. The difference in mean food chain length between streams was due largely to the presence of C. mexicanus at the spring stream. 7. Structural differences between the food webs of the spring and mountain streams were relatively minor. The difference in the proportion of macroinvertebrate biomass contributing to different trophic levels was major, however, indicating significant differences in the volume of material and energy flow between food‐web nodes (i.e. food web function).     

Seasonal variations in the benthos of a chalk trout stream,the River Samson,Belgium

Seasonal variations in the benthos of a Belgian chalk stream were investigated. Total biomass varies extensively over the year (30 to 100 g wet wt. m^–2). In summer, however, it is smaller than fish biomass. Densities range from 30 000 to 50 000 individuals m^–2, but the actual number of taxa is always near 60. Diversity indices (Shannon-Weaver and Pielou) exhibit slight fluctuations. Numerical indices are minimal in winter when the stream is in flood. Gravimetric indices are minimal in spring when biomass is maximal. Species-abundance curves almost always indicate a fauna with many rare species, with, also, some indication of a second maximum of moderately abundant species. Six taxa dominate: Oligochaeta, Gammarus fossarum, Ephemeroptera, Coleoptera, Trichoptera and Diptera. There are great fluctuations in their relative importance over a year. Thus, there seems to be a succession of peaks in densities of individual taxa permitting more efficient utilization of resources. However, biomass variations depend on the species involved. As a general rule, maximum biomass precedes maximum density.     

Littoral microcrustacea in Lake 302S in the Experimental Lakes Area of Canada: acidification and recovery

• 1 The littoral microcrustacean community (Cladocera and Copepoda) was examined from 1989 to 1991 in a lake experimentally acidified to pH 4.5, and from 1992 to 1997 during the early stages of pH recovery.
• 2 Cladoceran abundance declined significantly from 1989 to 1991 (pH 4.5), but species richness did not change. Acantholeberis curvirostris, Simocephalus serrulatus, Latona spp. (Latona setifera, L. parviremis), and all species of chydorid Cladocera declined markedly in abundance while at pH 4.5. The abundance of cyclopoid copepods was low and Ceriodaphnia and calanoid copepods were absent.
• 3 Recovery of the community was subsequently monitored as pH was incrementally changed to a target pH 5.1 in 1992 and 1993, and to 5.8 in 1994–97. Species richness remained unchanged. Chydorid cladocerans remained at low abundance in 1992, and only Chydorus cf. brevilabris increased substantially from 1993 to 1996. Non‐chydorid Cladocera increased in abundance in 1992, declined again in 1993, then gradually increased (mainly due to Ophryoxus gracilis) in 1994–96. All species declined in 1997 as minnows recolonized the lake. The calanoid copepod Leptodiaptomus minutus was present in low numbers in 1997.
• 4 The microcrustacean community in the littoral zone of Lake 302S has not yet shown consistent signs of recovery from acidification.

     

Salamander diversity alters stream macroinvertebrate community structure

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Changes in trophic state and aquatic communities in high Arctic ponds in response to increasing goose populations

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Effects of extreme low flows on freshwater shrimps in a perennial tropical stream

• 1 Long-term data on rainfall suggests that perennial rainforest streams rarely are subject to drying of riffles or pools in the wet, non-seasonal Caribbean climate of Puerto Rico. Unusually low rainfall in 1994 caused some headwater riffles to dry out completely, resulting in isolated pools, reduced pool volumes and loss of access to microhabitats by benthic invertebrates.
• 2 From 1992 to 1998, shrimp populations were sampled bimonthly using baited traps in six pools along 1200 m (from 305 to 480 m in altitude) of Quebrada Prieta, a second-order headwater stream in the Luquillo Experimental Forest (Caribbean National Forest).
• 3 Following contraction of the smaller and shallower pools in the most upstream section of the stream, mean densities of the dominant shrimp (Atya lanipes) increased from 22 to 75 shrimp m⁻² of pool area during the 1994 drought year. A second common species (Xiphocaris elongata) increased from 5 to 14 shrimp m⁻². A smaller percentage of adults of both species was gravid during the drought.
• 4 Following the 1994 drought (1995–1998), densities of both shrimp species and reproductive activity of Atya returned to predrought (1990–1993) levels. However, the reproductive activity of Xiphocaris remained lower than in the predrought period.
• 5 It is suggested that prolonged droughts, even in tropical rainforest biomes, may significantly alter aquatic communities through localised crowding effects resulting from habitat contraction, and lead to prolonged decreases in reproductive output. Consequently, major alterations in aquatic populations and communities would be predicted by current climate change scenarios of decreased total rainfall and increased variability.

     

Exotic crayfish in a brown water stream: effects on juvenile trout, invertebrates and algae

SUMMARY 1. The impact of the introduced omnivorous signal crayfish (Pacifastacus leniusculus) on trout fry, macroinvertebrates and algae was evaluated in a brown water stream in southern Sweden using in situ enclosures. We also examined the gut content of all surviving crayfish in the enclosures. Two crayfish densities in addition to a control without crayfish were used in replicate enclosures (1.26 m²) in a 1‐month experiment. Additionally, 20 trout fry (Salmo trutta) were stocked in each enclosure to assess the effects of crayfish on trout survival and growth. 2. Detritus was the most common food item in crayfish guts. Animal fragments were also frequent while algae and macrophytes were scarcer. Crayfish exuviae were found in crayfish guts, but the frequency of cannibalism was low. 3. Trout survival in enclosures was positively related to water velocity but was unaffected by crayfish. 4. Total invertebrate biomass and taxon richness were lower in crayfish treatments. The biomass of all predatory invertebrate taxa was reduced but only three of six non‐predatory taxa were reduced in the crayfish treatments. 5. Epiphytic algal biomass (measured as chlorophyll a, on plastic strips) was not related to crayfish density, whereas the biomass of epilithic algae (measured as chlorophyll a) was enhanced by high water velocity and high crayfish density. The latter was possibly mediated via improved light and nutrient conditions, as active crayfish re‐suspend and/or remove detritus and senescent algal cells during periods of low water velocity. 6. We conclude that the introduced signal crayfish may affect stream communities directly and indirectly. Invaded communities will have reduced macroinvertebrate taxon richness and the signal crayfish will replace vulnerable invertebrate predators such as leeches. In streams that transport large amounts of sediment or organic matter, a high density of crayfish is likely to enhance benthic algal production through physical activity rather than via trophic effects.     

Industrial road crossings drive changes in community structure and instream habitat for freshwater fishes in the boreal forest

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Interactive multiple‐stressor effects of the antibiotic monensin,cattle effluent and light on stream periphyton

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Shortcuts in biodiversity research: What determines the performance of higher taxa as surrogates for species?

Biodiversity research is often impeded by the time and resources required to identify species. One possible solution is to use higher taxa to predict species richness and community composition. However, previous studies have shown that the performance of higher taxa as surrogates for species is highly variable, making it difficult to predict whether the method will be reliable for a particular objective. Using 8 independent datasets, I tested whether higher taxa accurately characterize the responses of beetle and ant communities to environmental drivers. For each dataset, ordinations were carried out using species and higher taxa, and the two compared using the Procrustes m² statistic (a scale‐independent variant of Procrustes sum of squares). I then modelled the relationship between five hypothesised explanatory variables and 1) Procrustes m², and 2) the coefficient of determination (R²) for the correlation between richness of species and higher taxa. The species to higher taxon ratio, community structure, beta diversity, completeness of sampling, and taxon (beetles or ants) were all significant predictors of m², together explaining 88% of the variance. The only significant predictor of R² was the species to higher taxon ratio, which explained 45% of the variance. When using higher taxa to predict community composition, better performance is expected when the ratio of species to higher taxa is low, in communities with high evenness and high species turnover, and when there is niche conservation within higher taxa. When using higher taxa to predict species richness, effective surrogacy can be expected when the species to higher taxon ratio is very low. When it is not, surrogacy performance may be strongly influenced by stochastic factors, making predictions of performance difficult.     

Drought ecohydrology alters the structure and function of benthic invertebrate communities in mountain streams

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Influence of disturbance on insect communities in Pacific Northwest streams

Coniferous forests of the Pacific Northwest provide a unique setting for stream ecology research because of the great age of the forests and the important role of wood debris in structuring aquatic systems. The composition and diversity of the insect community in Mack Creek, a stream in a 450 yr conifer forest, was compared with that in Grasshopper Creek where it flowed through a recent clearcut, and at Quartz Creek, which had a 40 yr deciduous canopy. Of the 256 taxa identified, Mack Creek had the highest species richness (196) and evenness. The open site had 191 taxa but high dominance of a few grazer taxa. The deciduous-canopy site had 165 taxa with abundant detritivores. Despite differences in density, the biomass of emergence was similar at the three sites, ranging from 1.53 to 1.65 g m^–2 yr^–1.The importance of disturbance in structuring stream communities was demonstrated in phenomenological studies after a debris torrent at Quartz Creek, and by monitoring stream recovery following the eruption of Mt. St. Helens in 1980. At Quartz Creek, the debris torrent eliminated the fauna from a 300 m reach, but there was rapid recovery. Emergence density in the same year was similar to that of the control site. The major shift in populations was a decrease in detritivores and moss associates and an increase in grazers, especially Baetis mayflies.At Ape Creek on Mt. St. Helens, over 200 taxa were recorded by 1987 but most occurred in very low densities. This site is reset by winter freshets and by infilling with glacial fines in the summer so the fauna continues to be dominated by weedy, or early successional species. At Clearwater Creek, the presence of wood debris as a stable substrate and limited inputs of fine sediment after 1980 have hastened population recovery. A decade after the eruption this site can be characterized as being in the mid-stages of succession with high insect productivity from an algal-based food web. With further growth of the riparian vegetation I predict a shift towards a detritus-based food web and fauna more similar to Mack Creek than it is at present.     

Environmental effects on biofilm bacterial communities: a comparison of natural and anthropogenic factors in New Zealand streams

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