bluuebunny/crossref_metadata_2025_split huggingface dataset:
Continuing dispersal of freshwater triclads (Platyhelminthes; Turbellaria) in Britain with particular reference to lakes
Authors: Young J. O. , Reynoldson T. B. 
Published: March 2003

1. A survey of lakes in Anglesey and Snowdonia, Wales, in the summer of 1997 recorded changes in the triclad fauna which had occurred since earlier studies in the 1950s and in 1973. Two native species, Polycelis tenuis and Dugesia polychroa, and two immigrants, Planaria torva and especially Dugesia tigrina, have increased their range. The triclad fauna has remained unchanged with time in eleven out of sixteen lakes in Snowdonia, in contrast to only one out of fourteen lakes on Anglesey. This supports the hypothesis produced in the 1950s, that the triclad fauna of the ion‐poor, unproductive lakes in Snowdonia would change little with time, being maintained by ecological interactions, whereas the ion‐rich, productive lakes on Anglesey, from which native Dugesia spp. and Dendrocoelum lacteum are historically absent, would increase in triclad diversity.2. An examination of national records for the distribution of D. tigrina and Pl. torva indicated their continuing dispersal in both still and running waters in mainland Britain, with the former species having the greater frequency of occurrence.3. The reasons for this may be that D. tigrina is (a) more easily dispersed, (b) a more opportunistic, catholic feeder, (c) a more vigorous competitor, (d) able to reproduce asexually and (e) able to prey to some extent on other triclad species, as shown in the laboratory but not yet confirmed in the field. The absence of D. tigrina and Pl. torva from unproductive lakes may be explained in terms of low temperature and feeding mode, and a low standing crop of gastropods, respectively.4. Seven surveys (1961–1997) of the triclad fauna (six species) of Colemere, England, revealed that D. tigrina was confined to one small area of the littoral zone until the mid‐1980s, after which it spread fairly rapidly to occupy the entire shore by 1997. Its expansion has been to the detriment of all the native species, particularly P. tenuis, except Dd. lacteum. The possible extinction of Pl. torva may be linked to a numerical reduction in snails, particularly Potamopyrgus jenkinsi.5. Dugesia tigrina has an adverse effect on the native triclad fauna in lakes, particularly when only a few species are present. This has been explained in terms of the availability of a wider variety of food. The presence of a larger number of triclad species denies the immigrant food items, particularly crustaceans and snails, the food refuges of Dd. lacteum and Dugesia spp., respectively. However, the long‐term study of Colemere has shown that more diverse triclad faunas may also be vulnerable to this immigrant. The effect of Pl. torva on native triclads remains uncertain.
Effects of urbanization on streams of the Melbourne region, Victoria, Australia. II. Benthic diatom communities
Authors: Sonneman Jason A. , Walsh Christopher J. , Breen Peter F. , Sharpe Andrew K. 
Published: March 2003

1. Epilithic and epiphytic diatom community composition were assessed in small streams of the Melbourne region to test the effects of (a) urban density (sub‐catchment imperviousness 0–51%) and (b) stormwater drainage intensity (comparing the intensively drained metropolitan area with urban areas of the hinterland, which had open drains and some localized stormwater drainage).2. Communities separated into three groups: eastern hinterland, western hinterland and a metropolitan group. Separation of eastern and western hinterland groups, and of eastern and western sites within the metropolitan group were best explained by patterns of electrical conductivity, basalt geology and annual rainfall. Separation of metropolitan and hinterland groups, and patterns within the hinterland groups were best explained by nutrient gradients (phosphorus, ammonia and total nitrogen).3. Nutrient concentrations were not only apparently influenced by urban density but also by effluents from small sewage treatment plants and agricultural activities at a few sites.4. Species richness did not vary consistently between the metropolitan and hinterland groups but within the western hinterland, sites with low nutrient concentrations tended to be more species‐rich than mildly enriched sites.5. Composition of both diatom and macroinvertebrate communities (assessed in a concurrent study) were sensitive indicators of urban‐derived impacts. However, diatoms were better indicators of nutrient enrichment, while macroinvertebrates were better integrative indicators of catchment disturbance.
The impact of an introduced bivalve (Corbicula fluminea) on the benthos of a sandy stream
Authors: Hakenkamp Christine C. , Ribblett Suzanna G. , Palmer Margaret A. , Swan Christopher M. , Reid Janet W. , Goodison Mike R. 
Published: March 2003

1. The effect of an exotic, burrowing bivalve (Corbicula fluminea) on the benthic fauna of a sandy‐bottomed stream was assessed by field and laboratory experiments. Corbicula differs from other freshwater, non‐native bivalves in that it both filter‐ and pedal‐feeds and thus has the potential to influence the streambed community in different ways.2. In the field, cages were used to vary the abundance of Corbicula in the streambed. Increasing abundance of Corbicula was negatively associated with the abundance of benthic bacteria and flagellates but had no apparent effect on other protists or meiofauna.3. In the laboratory, we compared the effect of Corbicula on the benthic community when the bivalves were able both to filter‐ and pedal‐feed with that when they were able only to filter‐feed. Bivalves restricted to filter‐feeding were placed in sediment lacking benthic fauna and organic matter, then the benthos in nearby natural sediment was compared with the community present when Corbicula was able to move freely through the sediment and both to filter‐ and pedal‐feed. Corbicula able to pedal‐feed were again associated with a decreased abundance of benthic flagellates and bacteria, as well as diatoms.
Modelling growth of brown trout,Salmo trutta, in terms of weight and energy units
Authors: Elliott  , Hurley  
Published: March 2003

1. The chief objectives were: (i) to compare two growth models, one based on weight and the other on energy, using the same data set for the analyses; (ii) to discover if weight and energy units can be simply interchanged for growth assessment. The data set was for 183 brown trout,Salmo trutta(live weight 1–300 g), fed to satiation on shrimps,Gammarus pulex, and grown individually over 42 days at constant temperatures (range 3.8–20.4 °C).2. Rates of change in weight or energy content, and final weight or energy content at the end of 42 days growth, were estimated from the models and were excellent fits to the experimental data (P < 0.001). The shape of the temperature relationship for rates of change or final values was triangular for the weight model and curvilinear for the energetics model. Optimum temperatures for growth according to the weight and energetics models were 13.1 and 13.9 °C, respectively, for rates of change and 13.1 and 13.5 °C, respectively, for final values. When the growth period was extended to 100 and then 300 days, the triangular relationship and optimum temperature remained the same for the weight model, but the curvilinear relationship became more triangular for the energetics model and the optimum temperature identical to that in the weight model. The relationship between gross efficiency and temperature also differed in shape between the two models but maximum efficiencies occurred at a similar value of 9 ± 0.1 °C (18 and 32% for weight and energetics models). As fish weight increased, gross efficiency remained constant in terms of energy units, but decreased markedly in terms of weight.3. These comparisons showed that different conclusions can be drawn from the two models, even if the same data set was analysed. There was a close relationship between initial wet weight and energy content for stock trout used in the experiments, but the relationship was not so close at the end of the experiments, and interchangeability of units could no longer be assumed. A variable error, often as high as 10–12%, would occur if the relationship for initial values was used to predict one unit from the other. Therefore, weight and energy units cannot be simply interchanged for growth assessment, especially in comparisons for trout of different sizes.
Stable isotope analysis of macroinvertebrates and their food sources in a glacier stream
Authors: Zah Rainer , Burgherr Peter , Bernasconi Stefano M. , Uehlinger Urs 
Published: March 2003

1. Food sources and trophic structure of the macroinvertebrate community along a longitudinal gradient were examined in a glacier stream of the Swiss Alps (Val Roseg). Analysis of multiple stable isotopes (δ13C and δ15N) and measurement of C : N ratios were used to differentiate between allochthonous and autochthonous organic matter.2. Although isotopic signatures of algae varied widely among sites and dates, it was possible to discriminate between allochthonous and autochthonous food sources using a site‐specific approach.3. Dominant food sources of herbivorous invertebrates in all main channel sites were epilithic diatoms and the filamentous gold alga Hydrurus foetidus. Allochthonous organic matter was of some importance only in a groundwater‐fed stream close to the floodplain margin.4. Seasonal changes in the δ13C signature of the macroinvertebrates corresponded with seasonal changes in δ13C of the gold alga H. foetidus. This indicated that the energy base remains autochthonous throughout the year.5. Because of limited food sources, feeding plasticity of the invertebrate community was high. Both grazers and shredders fed predominantly on algae, whereas gatherer‐collectors seemed to be omnivorous.6. The overall enrichment of δ15N was 2.25‰ (r2=0.99) per trophic level. On a gradient from the glacier site to a downstream forested site trophic enrichment was constant but variation in δ15N within trophic levels decreased.
Length‐specific growth rates in freshwater mussels (Bivalvia: Unionidae): extreme longevity or generalized growth cessation?
Authors: Anthony James L. , Kesler David H. , Downing William L. , Downing John A. 
Published: March 2003

1. North American lacustrine freshwater mussels (Bivalvia: Unionidae) are one of the world’s most imperilled groups of organisms. Knowledge of their age structure and longevity is needed for the understanding and management of mussels. Current methods for age estimation in freshwater mussels are insufficient and may have resulted in an erroneous view of the ages of lacustrine freshwater mussels.2. We collected growth data through mark‐recapture in Minnesota and Rhode Island, U.S.A., examining four lentic populations of three of the most common species of freshwater mussels, Elliptio complanata, Lampsilis siliquoidea, and Pyganodon grandis. Using an inversion of the von Bertalanffy growth equation, we estimated age at length from length‐specific growth relationships.3. In some populations, lacustrine mussels may be much older than previously predicted. Ages predicted from actual growth rates suggest that individuals in some populations frequently reach ages in excess of a century, placing unionid mussels among the Earth’s longest‐lived animals. Alternatively, if growth has only recently slowed in these populations, generalized growth cessation may be occurring over a broad distributional range of some common North American lacustrine mussels.
Macroinvertebrate community structure in relation to environmental variables in a Swiss glacial stream
Authors: Lods‐Crozet Brigitte , Castella Emmanuel , Cambin Diana , Ilg Christiane , Knispel Sandra , Mayor‐Simeant Helene 
Published: March 2003

1. Benthic macroinvertebrate distribution was examined in relation to channel characteristics (including stability), substratum, hydraulic variables, primary production (chlorophyll a) and coarse particular organic matter (CPOM) in an alpine glacial stream, the Mutt (Upper Rhône valley, Switzerland). Co‐inertia analysis and canonical correspondence analysis were used to identify the major environmental gradients influencing community variations.2. The Mutt (length: 3.6 km, altitudinal range: 1800–3099 m a.s.l.) exhibited typical characteristics of a kryal stream. Average summer temperature remained below 2 °C immediately downstream from the snout but was on average 5 °C higher 1700 m downstream. Seasonal variations in water sources were evidenced by the high late‐summer (September) contribution of groundwater with increased conductivity.3. Sixty‐six taxa were recorded from the five reaches sampled at three periods (snowmelt, ice melt and low water in late summer) in 1996 and 1997, of which 29 were Chironomidae. Three taxa of Diamesinae were the first colonizers of the stream below the glacier, but 16 taxa, including Ephemeroptera, Plecoptera and Trichoptera, were already recorded 200 m downstream. Water depth, channel slope and Pfankuch’s Index of channel stability were strongly correlated with the longitudinal faunal gradient. Maximum temperature, current velocity and water conductivity were also correlated, but to a lesser extent.4. The rapid incorporation of non‐chironomid taxa into the stream community represented a departure from Milner & Petts’s (1994) conceptual model of invertebrate succession downstream of glacial margins. The results confirmed that glacial stream communities are primarily driven by physical determinants.
Long‐term effects of catchment liming on invertebrates in upland streams
Authors: Bradley David C. , Ormerod S. J. 
Published: March 2003

1. Catchment liming to mitigate acidification causes major chemical change in freshwaters but longer‐term effects are poorly understood. Using a replicated basin‐scale experiment with a multiple BACI design (= before‐after‐control‐impact), we assessed chemical and biological effects for 10 years after the catchments of three acidified Welsh streams at Llyn Brianne were limed in 1987/88.2. Stream chemistry was measured weekly to monthly, and macroinvertebrates monitored annually, between 1985 and 1998. Biological change through time was assessed from the abundance and taxon richness of invertebrates. We paid particular attention to 18 species known to be acid‐sensitive. The effects of liming were assessed by comparing chemical and biological trends among the three replicate limed streams, three acid reference streams and two naturally circumneutral streams.3. Following single lime applications, acid‐base chemistry in treated streams changed significantly. High mean pH (> 6), increased calcium (> 2.5 mg L−1) and low aluminium (< 0.1 mg L−1) persisted throughout the 10 years following liming.4. The effects of liming on invertebrates were modest. Acid sensitive taxa increased significantly in abundance in limed streams, but only during 2 years following treatment. Significant effects on richness were more sustained, but on average added only 2–3 acid‐sensitive species to the treated streams, roughly one‐third of their average richness in adjacent circumneutral streams. Only the mayfly Baetis rhodani and the stonefly Brachyptera risi occurred significantly more often in limed streams after treatment than before it.5. Despite these modest long‐term effects on invertebrates, nearly 80% of the total pool of acid‐sensitive species has occurred at least once in the limed streams in the 10 years since treatment. This pattern of occurrence suggests that the colonization of limed streams by acid‐sensitive taxa reflects limited persistence rather than restricted dispersal. We present evidence to show that episodes of low pH continued to affect acid‐sensitive taxa even after liming. We highlight the importance of extending the time‐periods over which the effects of large‐scale ecological experiments are assessed.
Time spent in the drift by downstream‐dispersing invertebrates in a Lake District stream
Authors: Elliott J. M. 
Published: March 2003

1. The objective was to determine the time spent in the drift by different taxa of stream invertebrates. Most data were obtained from an earlier experimental study to determine the distances travelled by drifting invertebrates of 16 taxa in Wilfin Beck. Experiments were performed at two sites: ‘site 4’ in a stony, fast‐flowing, section of stream, ‘site 3’ in a deeper stream section where macrophytes were abundant.2. The significant relationship between the mean distance x (m) travelled in the drift and modal water velocity V (m s−1) was described by a power function in the earlier study but, as the power was close to one, a linear relationship has now been found to provide a satisfactory model. The rate of increase in x (m) with increasing V varied considerably between taxa. The mean time [mean t (s)] spent in the drift was estimated by dividing each x (m) by the appropriate V. Mean t (s) for each taxon was usually very constant over a wide range of V at each site (0.10–0.60 m s−1 at site 4, 0.15–0.53 m s−1 at site 3). A simple model estimated the time spent in the drift by different percentages (e.g. 75, 50, 10 and 1%) of the drifting invertebrates.3. The experimental taxa at site 4 were divided into three groups according to the mean time spent in the drift. Mean t (s) for the five taxa in group 1 (32.8 s) was not significantly different from that obtained in control experiments with a mixed group of dead invertebrates. A similar time (33.0 s) was obtained for the five taxa in group 2, except at water velocities less than 0.2 m s−1 when the mean t (s) decreased to 15–21 s. Mean t (s) was constant for each of the six taxa in group 3, and significantly less than that for groups 1 and 2. Mean values ranged from 28.8 s for Ephemerella ignita to only 9.4 s for Baetis rhodani and Gammarus pulex. All mean values were lower at site 3, presumably because of the dense stands of macrophytes, with mean values of 12.9 s for the five taxa in group 1 (equalling the value for dead invertebrates). Mean values for the six remaining taxa varied from 6.4 s for Simulium spp. to only 4.9 s for Baetis rhodani and 4.8 s for Gammarus pulex. It was concluded from a discussion of this study that the time spent in the drift may provide a useful measure for comparing the downstream dispersal of invertebrates in different streams, and may be a useful addition to models for the drift feeding of salmonids.
The function of the suckers of larval net‐winged midges (Diptera: Blephariceridae)
Authors: Frutiger Andreas 
Published: March 2003

1. Larval net‐winged midges (Diptera: Blephariceridae) possess six ventral suckers that enable them to inhabit swift streams. Each sucker consists of a suction disc and a cavity with a piston. Large muscles are inserted within the piston, as well as at the base of the suction disc. This structure infers that both attachment and release of the sucker is achieved by vertical movements of the piston.2. Live observations of blepharicerid larvae revealed that the sucker is indeed attached by an upward movement of the piston, but that the cavity is flooded when the sucker is released. The piston is lowered only at the end of a sucker ‘step’, expelling water from the cavity.3. During foraging, the maxilla and the piston of the first sucker are moved synchronously, indicating that the first sucker functions as a holdfast thus facilitating grazing.4. The adhesive forces, as well as the relative size of blepharicerid suckers, differ amongst species. They are highest in Hapalothrix lugubris and lowest in Liponeura cordata, which correlates with the hydraulic stress to which the larvae of these species are exposed in their preferred habitat. The balance between the efficiency of their retention structure and the hydraulic conditions of their preferred habitat defines a key dimension of their ecological niche.
Competition in variable environments: experiments with planktonic rotifers
Authors: KIRK KEVIN L. 
Published: March 2003

1. In a constant environment, competition often tends to reduce species diversity. However, several theories predict that temporal variation in the environment can slow competitive exclusion and allow competing species to coexist. This study reports on laboratory competition experiments in which two pairs of planktonic rotifer species competed for a phytoplankton resource under different conditions of temporal variability in resource supply.2. For both species pairs, Keratella cochlearis dominated under all conditions of temporal variability, and the other species (Brachionus calyciflorus or Synchaeta sp.) almost always went extinct. Increasing temporal variation in resource supply slowed competitive exclusion but did not change competitive outcome or allow coexistence.3. Rotifers show a gleaner–opportunist trade‐off, because gleaner species have low threshold resource levels (R*) and low maximum population growth rates, while opportunist species have the opposite characteristics. In the competition experiments, the gleaner always won and the opportunists always lost. Thus, a gleaner–opportunist trade‐off was not sufficient to facilitate coexistence under conditions of resource variability. Instead, the winning species had both the lowest R* and the greatest ability to store resources and ration their use during times of extreme resource scarcity.
Life history variability of a grazing stream insect (Liponeura cinerascens minor; Diptera: Blephariceridae)
Authors: Frutiger Andreas , Buergisser Gabriella Meier 
Published: March 2003

SUMMARY 1. Fourteen populations of Liponeura cinerascens minor from different sites in the Swiss Alps were investigated. Our goals were to describe the life history of this blepharicerid species and to analyse how it was influenced by temperature and food availability.2. Temperature regimes and periphyton density at the sampling sites varied considerably. Mean annual temperature ranged from 3.8 to 6.5 °C, with annual amplitudes (i.e. the difference between the mean of the coldest and the warmest month) between 3.7 and 12.0 °C. Averaged periphyton density, which was assessed semiquantitatively on a scale from 0 to 5, ranged from 1.1 to 3.3.3. Larvae or pupae of L. c. minor were found between January and October. Presence of larvae or pupae at individual sites ranged from 100 to 224 days and appeared to be mainly a result of hatching patterns. Individual larval development required between 7 and 20 weeks. Our findings suggest that L. c. minor is univoltine and undergoes an extended (≥4 months) egg dormancy during late summer, autumn and winter.4. Development of L. c. minor was observed from <1 to 15.8 °C, indicating it is a cold‐stenotherm. Its geographical distribution seems to be constrained by high summer temperatures. Within the tolerated temperature range (0–16 °C), however, temperature had no apparent effect on hatching, larval growth rate or pupal size.5. Larval growth rate and size of pupae were significantly correlated with food availability. Completion of larval development required 300–400 degree‐days at sites where periphyton was readily available, but >800 degree‐days where periphyton availability was low.6. No evidence for intraspecific food competition was found, whereas food competition by other blepharicerid species, mainly Hapalothrix lugubris, appeared to be a major reason for the observed food limitation. However, as L. c. minor is much more widespread than H. lugubris, food competition between these two species is likely to occur infrequently. We therefore contend that variations in the life history of L. c. minor are mainly a consequence of its thermal constraints.