bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recolonization by benthic invertebrates after experimental disturbance in a Swiss prealpine river
Authors: MATTHAEI CHRISTOPH , UEHLINGER URS , MEYER ELISABETH , FRUTIGER ANDREAS 
Published: November 2003

1. Although the crucial point of disturbance experiments in streams is the extent to which they can simulate an actual spate, this aspect has been widely neglected in the design of such studies. Similarly, the influence of the specific hydrological disturbance regime of a stream on its benthic community has received much theoretical attention in recent years, but hypotheses have rarely been tested in the field.2. Our field experiment compared the structure of the benthic invertebrate community in the prealpine River Necker in north‐eastern Switzerland with predictions of the patch dynamics concept about the faunal composition of frequently disturbed streams. We also compared the resistance and resilience of the invertebrates between two sites in the River Necker. A similar substratum composition at both sites, but higher shear stress values both at baseflow and bankfull discharge at site 2, implied a higher disturbance frequency at the latter site. Five patches of stream bed of ≈ 9 m2 were disturbed by kicking and raking at each site, while five similar areas served as controls. From each plot, six Surber samples were taken: the first immediately after the disturbance, and the following five 1, 3, 6, 10 and 30 days later.3. Resilience of the total benthic invertebrate fauna was high. The total number of individuals recovered to undisturbed densities within 30 days at site 1 and 6 days at site 2. Taxon richness recovered within 3 days. In accordance with theory, taxa with high recolonization rates made up a major percentage of the total number of individuals, especially in disturbed plots. However, this percentage was lower at site 2 in spite of the higher disturbance frequency at this site. Rhithrogena spp., Leuctra spp. and the Simuliidae recovered faster to undisturbed densities at site 2. In contrast, absolute recolonization rates of these taxa were higher at site 1, where total invertebrate densities were more than twice as high as at site 2.4. Our results suggest that the time since the last disturbance should be considered as an important factor in studies of benthic invertebrate communities in prealpine rivers, because disturbances can alter the community structure. In frequently disturbed streams, very short sampling intervals may be needed to detect differences in taxon‐specific colonization rates. The specific hydrological disturbance regime of such streams is also important, because even within‐stream differences in the resilience of the benthic invertebrate community are possible.
Genetic differentiation in Daphnia obtusa: a continental perspective
Authors: HEBERT PAUL , FINSTON TERRIE 
Published: November 2003

1. The restricted scale of most prior studies of genetic diversity in daphniid populations provides limited information on the geographical patterning of gene frequencies. The present study addresses this gap by examining allozymic divergence in populations of the most broadly distributed daphniid in the warm temperate regions of North America, Daphnia obtusa, across its range.2. Local populations of this species show the gene frequency differentiation typical of other daphniids. In contrast to other daphniids with broad distributions, however, further divergence is apparent at a larger geographical scale, with North American D. obtusa fragmented into three lineages showing largely allopatric distributions. The three lineages are based primarily on allele frequency shifts at three polymorphic loci and are represented by eastern, central and south‐western groupings.3. Because of this pattern of differentiation, there is no simple monotonic relationship between geographical distance and genetic divergence. Instead, local metapopulations belonging to a specific lineage show little genetic divergence over several thousand km, while marked shifts in gene frequency occur over a few hundred km in regions where different lineages are in contact.
The influence of a river bird, the dipper (Cinclus cinclus), on the behaviour and drift of its invertebrate prey
Authors: JENKINS R.K.B. , ORMEROD S.J. 
Published: November 2003

1. We examined the behavioural response of stream macroinvertebrates to real and simulated predatory activity by a river bird, the Eurasian dipper, Cinclus cinclus L.2. In the field, we assessed whether invertebrate drift changed in response to live dippers in enclosures; we found no effects on the drift of any of the five families for which individual analyses were possible, either because it was infrequent, or involved distances too short to be detected (< 0.5 m).3. In a laboratory stream, we observed prey during encounters with a model dipper which simulated flight, swimming, bill contact with the prey, and stone turning. Invertebrate families varied in their response. Simuliids and hydropsychid caddis lacked effective escape behaviour, consistent with heavy losses through predation by dippers in the wild. Other families either drifted (Baetidae, Gammaridae) or moved away (Heptageniidae, Ephemerellidae, Leuctridae, Perlidae) from the model dipper, but responded only to bill contact or simulated stone turning. Such delayed responses would not protect individuals directly targeted by foraging dippers and partly explain the lack of detectable effects by dippers on drift in the field.4. We suggest why invertebrates do not show more marked escape responses to this important predator.
The relationships among three habitat scales and stream benthic invertebrate community structure
Authors: CARTER J.L. , FEND S.V. , KENNELLY S.S. 
Published: November 2003

1. The relationships between three habitat scales and lotic invertebrate species composition were investigated for the 15 540 km2 Yakima River basin in south‐central Washington, U.S.A.2. The three spatial scales were sample (the sampled riffle), reach (a length of ten–twenty stream widths) and segment (a length of stream of nearly uniform slope and valley form having no change in stream order).3. Physical variables were highly correlated between scales and expressed a relationship between altitude, basin form and small‐scale physical structure.4. Multiple discriminant function analyses indicated that segment‐ and reach‐scale variables discriminated among species‐defined groups better than sample‐scale variables.5. Species composition varied along a complex altitudinal gradient of changing basin form and resultant land use.6. There was no clear relationship between species richness and altitude on a site basis. However, when viewed at the basin scale, maximum richness was observed at the transition between montane and valley sites.
Sediment‐related growth limitation of Elodea nuttallii as indicated by a fertilization experiment
Authors: BEST E.P.H. , WOLTMAN H. , JACOBS FH.H. 
Published: November 2003

1. A fertilization experiment was performed to identify the limiting nutrient for the growth of submerged vegetation in ditches of a peat‐grassland system in the Netherlands, in which restoration measures involved ceasing fertilization, exporting nutrients by removal of above‐ground plant mass and large‐scale introduction of calcium‐rich, nutrient‐poor artesian water.2. Growth of Elodea was significantly enhanced by enrichment with nitrogen alone, and by fertilization with nitrogen in combination with phosphorus, and by nitrogen in combination with phosphorus and potassium.3. Plant tissue nutrient concentrations increased significantly, for nitrogen by enrichment with nitrogen alone, and with nitrogen in combination with phosphorus and potassium; for phosphorus by enrichment with phosphorus alone and with phosphorus in combination with nitrogen and potassium; tissue concentrations of potassium were not enhanced by any treatment.4. The elemental ratios of treated plants indicated that nitrogen, rather than phosphorus, was limiting in all treatments, except in those involving nitrogen and NK enrichment (when phosphorus was limiting).5. The efficiency with which plants used nutrients declined with increased supply of nitrogen and phosphorus, but was unchanged when potassium was increased. Efficiencies were similar to those of other aquatic macrophytes.
Grazing by a native and an exotic crayfish on aquatic macrophytes
Authors: NYSTRÖM PER , STRAND JOHN 
Published: November 2003

1. We compared grazing by native noble crayfish (Astacus astacus) and the exotic signal crayfish (Pacifastacus leniusculus) on seedling or well‐established macrophytes.2. In a pool experiment, seedlings of emergent Scirpuslacustris and floating‐leaved Potamogetonnatans were heavily grazed by adult signal crayfish, whereas established plants of the same species sustained only minor damage.3. In a preference experiment two submerged macrophytes (Charavulgaris and Elodeacanadensis), and both seedlings and established plants of S. lacustris and P. natans, were presented pairwise to signal and noble crayfish. There was no significant difference in preference by the two crayfish species. Chara vulgaris was preferred to all other plants presented, established plants of S. lacustris and P. natans were never preferred, and seedlings of P. natans were preferred to established P. natans.4. An aquarium experiment was conducted in which the consumption of Chara by signal and noble crayfish was measured in relation to water temperature. Signal crayfish consumed significantly more Chara than noble crayfish, especially at higher temperatures.5. Our results indicate that the signal crayfish is the more voracious grazer especially at higher temperatures. There may be negative effects on vegetation (emergents and floating‐leaved, as well as submerged species) when the signal crayfish is introduced. Chara species are particularly susceptible, since they are preferred by crayfish and the genus includes a large number of rare species. Stocking of crayfish therefore could lead to the decline or removal of submerged species in order of crayfish feeding preferences and could prevent the spread or cause a decline of emergent and floating‐leaved vegetation.
Potential fragmentation and loss of thermal habitats for charrs in the Japanese archipelago due to climatic warming
Authors: NAKANO SHIGERU , KITANO FUMIAKI , MAEKAWA KOJI 
Published: November 2003

1. The upper thermal limits of the present distributions of two charr species, Dolly Varden, Salvelinus malma, and white‐spotted charr, S. leucomaenis, in streams of the Japanese archipelago were examined using groundwater temperature as an index of thermal condition. The lower limits of the altitudinal distributions of Dolly Varden and white‐spotted charr were delineated, respectively, by 8 and 16 °C groundwater isotherms.2. The potential impact of future climatic warming on the geographical distribution, habitat extent and population fragmentation of each species was predicted at both the full archipelago and individual catchment levels.3. For Dolly Varden, analysis at the full archipelago level indicated a loss of 27.6, 67.2, 79.6 and 89.6% of the current geographical range, respectively, for a 1, 2, 3 and 4 °C increase in mean annual air temperature. The present distribution area of white‐spotted charr would likewise reduce by 4.1, 20.5, 33.8 and 45.6%, respectively.4. Based on the analyses of three individual catchments, one for Dolly Varden and two for white‐spotted charr, the lower habitat boundaries for the two charr species could be expected to rise increasingly to higher elevations in each catchment as warming proceeded. As a consequence, there would be large reductions in mean habitat area, with increasing habitat fragmentation followed by localized extinctions of the two species.
Patterns in benthic food webs: a role for omnivorous crayfish?
Authors: NYSTRÖM PER , BRÖNMARK CHRISTER , GRANÉLI WILHELM 
Published: November 2003

1. The biomass and species richness of macrophytes and invertebrates in artificial ponds at two sites in southern Sweden (twenty‐one ponds at each site) were investigated. Alkalinity was high at one site (H ponds) and low at the other site (L ponds). The ponds chosen had different densities of signal crayfish (Pacifastacus leniusculus), with mean crayfish abundance (estimated by trapping and expressed as catch per unit effort) significantly higher in the L ponds (10.7) than in the H ponds (4.9). Macrophytes, invertebrates, the amount of periphyton on stones and the organic content of the sediment were determined in each pond.2. Macrophyte biomass, cover and species richness declined with increasing crayfish density. Macrophyte species composition differed between ponds and was related to crayfish abundance.3. The total biomass of invertebrates and the biomass of herbivorous/detritivorous invertebrates declined with increasing crayfish abundance, but the biomass of predatory invertebrates declined only in the L ponds. The relative biomass of Gastropoda and Odonata declined in ponds where crayfish were abundant. In ponds where crayfish were abundant the invertebrate fauna was dominated by sediment‐dwelling taxa (Sialis (H and L ponds) and Chironomidae (H ponds)).4. The number of invertebrate taxa in macrophytes declined with increasing crayfish abundance. The percentage of macrophyte‐associated invertebrate taxa differed between ponds, but also between sites. The relative biomass of Gastropoda declined in H ponds where crayfish were abundant. In H ponds Trichoptera or Gammarus sp. and Heteroptera dominated where crayfish were abundant, whereas Odonata dominated in L ponds with abundant crayfish.5. The organic content of the sediment decreased in ponds with high crayfish densities, while the amount of periphyton on stones was not related to crayfish density.6. We conclude that the signal crayfish may play an important role as a keystone consumer in pond ecosystems, but lower trophic levels did not respond to changes in the abundance of the crayfish according to the trophic cascade model. Omnivorous crayfish may decouple the cascading effect.
Tropical acid streams – the chironomid (Diptera) response in northern Australia
Authors: CRANSTON P.S. , COOPER P.D. , HARDWICK R.A. , HUMPHREY C.L. , DOSTINE P.L. 
Published: November 2003

1. Chironomidae, sampled by interception of drifting cast pupal exuviae, responded to inputs of acid, heavy metal‐rich waters in a seasonally flowing tropical stream in northern Australia.2. Responses included gain of distinctive (indicative) taxa, loss of some species typical of pristine conditions, and increase in species richness.3. Experimental manipulation (upstream diversion) of a mine adit entry showed that these responses were the result of change in water quality.4. The higher species richness at low pH, which is contrary to temperate studies, may be explained by the large tropical (Australian and south‐east Asian) pool of species tolerant of naturally occurring acidic aquatic habitats.5. The structure and responses of the exuvial‐assessed chironomid community matched long‐term larval data.
A classification of mixotrophic protists based on their behaviour
Authors: JONES HARRIET 
Published: November 2003

1. Mixotrophs are organisms which combine phototrophy and heterotrophy; such nutritional behaviour is widespread among protists. This ability to combine multiple modes of nutrition varies between species and is not related to their taxonomic grouping. A classification of mixotrophic protists, based on their behaviour, is proposed, dividing them into four groups.2. Group A includes protists whose primary mode of nutrition is heterotrophy and where phototrophy is employed only when prey concentrations limit heterotrophic growth. In groups B, C and D phototrophy is the dominant mode of nutrition. In group B phagotrophy supplements growth when light is limiting, therefore ingestion of prey is inversely proportional to light intensity; in group C phagotrophy provides essential substances for growth and ingestion is proportional to light intensity; and group D includes those who have very low ingestion rates, ingesting prey only, for example, for cell maintenance during prolonged dark periods.3. This classification is aimed towards predicting the impact of any particular mixotrophic protist on the aquatic food web, and how this impact may vary depending on the environmental conditions. A model representation of the four groups is discussed.
Response of invertebrates to lotic disturbance: is the hyporheic zone a patchy refugium?
Authors: DOLE‐OLIVIER M.‐J. , MARMONIER P. , BEFFY J.‐L 
Published: November 2003

1. Natural experiments, in the form of disturbance from spates, were used to study the resistance and resilience of interstitial communities. Investigations were conducted in a by‐passed section of the Rhône River characterized by an artificial hydrology with frequent spates separated by regular minimum discharge of 30 m3 s–1.2. Three areas of a bar were studied, upwellings at the head of the bar (stations 1 and 2), and downwelling at the tail of the bar (station 3). In the head of the bar the substratum was characterized by stable cobbles, while mobile gravels dominated in the tail of the bar. At each station, samples were derived from four depths (0.5, 1.0, 1.5 and 2.0 m below the surface of the substratum). Fifteen spates occurred during the study period whose peak discharge ranged from 50 to 1640 m3 s–1. Temporal variations of the fauna were studied by comparing the spate effect observed 1 day (resistance), 7 days (resilience) and 17 days after the spate. Within‐class correspondence analysis was used to compare the temporal variability of the fauna within each class {station/depth}.3. The fauna differed markedly between the three stations, and the relative density of stygobionts (i.e. hypogean fauna) decreased from 55% at station 1 to 4% at station 3. The spatio‐temporal variability increased dramatically from station 1 to station 3.4. The results suggest that the hyporheic zone acts as a patchy refugium: the stations were more or less active refugial zones, depending on hydrology (upwelling or downwelling), substratum stability and spate amplitude.5. The downwelling station was the main refugium area for benthic taxa. Important migrations of benthic groups (e.g. Gammarus, Cladocera) or hyporheic taxa (e.g. Cyclopoida and Harpacticoida) were observed deep into the sediment (2 m). Vertical movements of stygobionts (Niphargus, Niphargopsis) were also observed at high amplitude spates. These movements were very important (great numbers of individuals migrated) at low and medium magnitude spates, but were unimportant at high discharge, when the threshold of sediment instability was exceeded. In this case the substratum became mobile and induced drift of benthic organisms.6. Conversely, in the upwelling stable stations, accumulation was less important (lower number of species and lower densities) but more constant with increasing discharge, suggesting that substratum stability is also a key factor.7. Generally recovery was rapid at all stations (within 7 days) but no relationships were found between resilience (rate of recovery) and the amplitude of spates.
Spatial pattern, patch dynamics and successional change: chironomid assemblages in a Lake Erie coastal wetland
Authors: BOTTS P. 
Published: November 2003

1. Distribution patterns in 1994 and 1995 of chironomid larvae in the sediments of wetlands on Presque Isle, Pennsylvania were used to determine whether relationships exist among species composition and wetland age, position or environmental characteristics. Canonical correspondence analysis was used to relate wetland age, degree of isolation, vegetation abundance and water chemistry to species composition.2. Of forty‐two chironomid taxa collected, Tanytarsus lugens group, Paratanytarsus sp. and Cladotanytarsus mancus group were the most widespread, but Lauterborniella agrayloides, Stictochironomus sp. and Cryptochironomus sp. were locally abundant in several sampling sites.3. The canonical ordination based on all site characteristics was statistically significant and accounted for 54.9% of the variance in the species data and 69.5% of the variance in the species–environment relationship. The variables that contributed significantly to the ordination model were macrophyte abundance, conductivity and wetland area.4. Partial canonical ordination based on environmental conditions with wetland age and position effects as covariables showed that environmental conditions explain a significant proportion of the variance in species composition among sites. Neither wetland age nor position variables explain a significant proportion of the variance in species composition.
Long‐term exposure of Boeckellagibbosa (Copepoda, Calanoida) to in situ levels of solar UVB radiation
Authors: ZAGARESE HORACIO , WILLIAMSON CRAIG , VAIL TIMOTHY , OLSEN OLAF , QUEIMALIÑOS CLAUDIA 
Published: November 2003

1. The freshwater calanoid copepod Boeckella gibbosa is typical of high elevation lakes and ponds in Patagonia (Argentina). Previous studies have shown that this species is highly tolerant to short‐term exposure to natural and artificial UVB radiation, and that its tolerance is due to photoreactivation by longer wavelength radiation. In this study, we investigate the potential sublethal effects of solar radiation after prolonged exposure.2. We incubated B. gibbosa at 1 m depth in oligotrophic Lake Toncek for 24 days. The incubation chambers were 1.2 l acrylic cylinders covered with appropriate filters in order to obtain three radiation treatments: visible radiation only, visible radiation + UVA and visible radiation + UVA + UVB.3. The three treatments did not differ significantly in variables considered as indicators of survival (number of individuals), reproduction (proportion of ovigerous females, clutch size) and development (instar composition). Although resistance to solar UVB radiation is certainly a requisite to live in transparent high elevation habitats, the fact of being effectively exposed to natural levels of UVB radiation does not seem to have measurable consequences on an already adapted species, such as B. gibbosa
How much water does a river need?
Authors: RICHTER BRIAN , BAUMGARTNER JEFFREY , WIGINGTON ROBERT , BRAUN DAVID 
Published: November 2003

1. This paper introduces a new approach for setting streamflow‐based river ecosystem management targets and this method is called the ‘Range of Variability Approach’ (RVA). The proposed approach derives from aquatic ecology theory concerning the critical role of hydrological variability, and associated characteristics of timing, frequency, duration, and rates of change, in sustaining aquatic ecosystems. The method is intended for application on rivers wherein the conservation of native aquatic biodiversity and protection of natural ecosystem functions are primary river management objectives.2. The RVA uses as its starting point either measured or synthesized daily streamflow values from a period during which human perturbations to the hydrological regime were negligible. This streamflow record is then characterized using thirty‐two different hydrological parameters, using methods defined in Richter et al. (1996). Using the RVA, a range of variation in each of the thirty‐two parameters, e.g. the values at ± 1 standard deviation from the mean or the twenty‐fifth to seventy‐fifth percentile range, are selected as initial flow management targets.3. The RVA targets are intended to guide the design of river management strategies (e.g. reservoir operations rules, catchment restoration) that will lead to attainment of these targets on an annual basis. The RVA will enable river managers to define and adopt readily interim management targets before conclusive, long‐term ecosystem research results are available. The RVA targets and management strategies should be adaptively refined as suggested by research results and as needed to sustain native aquatic ecosystem biodiversity and integrity.