bluuebunny/crossref_metadata_2025 huggingface dataset:
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.
Learning from the past: palaeohydrology and palaeoecology
Authors: BROWN A. G.
Published: March 2003

Attempts to increase European biodiversity by restoring rivers and floodplains are based on inadequate data on natural systems. This is particularly the case for NW European rivers because all catchments have been impacted by agriculture and river engineering. If river restoration is to have an ecological, as opposed to `cosmetic' design basis then baseline models are required. However, this poses three questions; (a) what is the natural river‐floodplain state, (b) how can it be defined and modelled and (c) can this state be recreated today? The first two questions can only be addressed by using palaeohydrological and palaeoecological data. A second and equally vital consideration is the stability/instability of any restored system to change in external forcing factors (e.g. climate) and in this context it may not be realistic to expect baseline models to provide equilibrium solutions but instead to define process‐form domains. Over the last two decades evidence has accumulated that the natural state of lowland rivers in much of NW Europe was multi rather than single thread‐braided, anastomosing or anabranching. Until recently our knowledge of floodplain palaeoecology was generally derived from pollen diagrams, which have source‐area of problems and lack of taxonomic specificity. The precision and breadth of palaeoecological reconstruction (including richness and structure) has been greatly increased by the use of multiple palaeo‐indicators including macrofossils, diatoms and beetles. The dynamics of small to medium sized, low‐energy, predeforestation floodplains were dominated by disturbance (windthrow, beavers, etc.) and large woody debris. In order to compare the hydrogeomorphological basis of floodplain ecology, both temporally and spatially, a simple index of fluvial complexity is presented. Palaeoecological and geomorphological investigations have the potential to provide in‐depth models of the natural range of channel conditions and sensitivity to external change that can be used to provide a scientific basis for floodplain restoration. There is also the possibility that floodplain‐channel restoration may be a valuable tool in the mitigation of future geomorphological change forced by climatic instability.
Correlations between observed dispersal capabilities and patterns of genetic differentiation in populations of four aquatic insect species from the Arizona White Mountains, U.S.A.
Authors: Miller Mark P. , Blinn Dean W. , Keim Paul
Published: March 2003

SUMMARY 1. Dispersal ability is an important ecological factor that can influence population structure. In an attempt to determine the extent that the pattern of genetic differentiation is correlated with dispersal ability in stream‐dwelling aquatic insects, we used the amplified fragment length polymorphism (AFLP) technique to characterise genetic variation in four aquatic insect species: Gumaga griseola (Trichoptera: Sericostomatidae), Helicopsyche mexicana (Trichoptera: Helicopsychidae), Psephenus montanus (Coleoptera: Psephenidae) and Ambrysus thermarum (Hemiptera: Naucoridae). Individuals were sampled from several sites within two adjacent catchments in the Arizona White Mountains. In addition to the genetic analyses, a 20‐week‐long trapping study was used to determine the relative dispersal ability of adults of the four species examined.

2. We obtained hierarchical indicators of genetic differentiation for catchments, sites within catchments and sites across the region examined. Overall, average estimators of genetic differentiation (F‐statistics) were consistent with direct observations of organismal movement, although it was our direct observations on adult insect flight that permitted us to interpret our results correctly. This was because of the fact that a lack of genetic differentiation across watersheds can be interpreted in two ways.

3. In contrast to F‐statistics, patterns of genetic isolation by distance for each species more clearly reflected dispersal ability, suggesting that such analytical approaches provide less ambiguous information about the importance of gene flow in the hierarchical partitioning of genetic variation in stream organisms.
Geomorphic dynamics of floodplains: ecological implications and a potential modelling strategy
Authors: RICHARDS KEITH , BRASINGTON JAMES , HUGHES FRANCINE
Published: March 2003

1.  The dynamics of channel migration and floodplain renewal constitute an important control of the ecological diversity of river corridors. Restoration initiatives should therefore assess whether these dynamics must be reinstated in order to address the cause rather than the symptoms of floodplain biodiversity decline.

2.  Restoration of reach‐scale dynamism in rivers where this is a natural behavioural process will restore smaller‐scale geomorphological and sedimentological processes that encourage vegetation regeneration, but may require catchment‐scale management of material flows.

3.  Channel dynamics depend on the style of river–floodplain interaction, and this may be summarised in qualitative, classificatory, sedimentological models of floodplain architecture that have been somewhat neglected in the ecological literature.

4.  One approach to the assessment of floodplain biodiversity and its restoration would be through the development of simulation models based on specified channel styles, and involving simplified hydrodynamics and successional changes. Such models, currently the subject of research as a spin‐off from modelling studies of landscape evolution, would permit evaluation of the consequences for ecological diversity of implementing various management options that may affect the dynamics of channel migration.
Functional heterogeneity of dry‐season fish refugia across a Mediterranean catchment: the role of habitat and predation
Authors: Magalhães M. Filomena , Beja Pedro , Canas Catarina , Collares‐Pereira Maria João
Published: March 2003

SUMMARY 1. Fish in Mediterranean streams survive through the summer in residual surface waters, encompassing a broad range of abiotic and biotic conditions. Yet, the extent to which fish assemblages may be shaped by functional heterogeneity in dry‐season refugia is largely unknown. This study addresses this issue, by examining fish assemblage and population attributes, and predation patterns in residual summer habitats (12 pools and six runs) across a Mediterranean catchment in south‐west Portugal.

2. Species richness was fairly constant among runs but increased with pool size, with the addition of exotics and rare natives to large pools resulting in nested subsets. The four most common species (chub, nase, loach and eel) were considered generalists in terms of their use of dry‐season refugia. Conversely, rare species presented more specialised habitats, with barbel and exotics favouring pools and stickleback favouring runs.

3. Age and size of the two most common species varied among dry‐season habitats. Age 0 chub were restricted to runs, where spawning stages (age 2 and older fish) were also more represented. Age 0 nase also concentrated in runs, but the individuals collected in pools exhibited greater growth. Conversely, age 2 and older nase were proportionally more abundant in pools, but with greater growth and better condition in runs.

4. The otter was the main fish predator, consuming fish of all species and size classes, irrespective of habitat. Otter activity concentrated in pools, where predation risk for cyprinids seemed to be much higher than in runs.

5. Dry‐season refugia apparently vary in functional importance for different fish species and life stages, acting as complementary units in the landscape. Therefore, the presence of both pool and run refugia trough the summer dry season may play a critical role in promoting the persistence of native species in Mediterranean streams.
Temperature‐ and predator‐induced phenotypic plasticity in Bosmina cornuta and B. pellucida (Crustacea: Cladocera)
Authors: Kappes Heike , Sinsch Ulrich
Published: March 2003

SUMMARY 1. Clones of Bosmina cornuta and B. pellucida (B. longirostris species complex) were derived from samples collected from Scheuermühlenteich and Lake Windsborn(westernGermany). Experimental temperature change (to 10 °C and 20 °C) and exposure to Acanthocyclops vernalis copepods (12 L−1) significantly altered external morphology in laboratory cultures of the two species. Morphological traits were derived from eight log10‐transformed and standardised morphometric distances by factorial analysis: factor 1 represented body size, factor 2, size of appendages and factor 3, the head size.

2. Acclimation of clones to cold water (10 °C, >14 days) led to an increase in body, antennule and mucrone size in B. cornuta and B. pellucida. Moreover, at 10 °C, B. cornuta cultures usually collapsed within a few weeks. Compared to the trials at 10 °C, acclimation to 20 °C (the two species) and to 15 °C (B. pellucida only) left the size of body appendages unchanged. Individuals were unequivocally assigned to each species by discriminant functions. Conspecific individuals that were acclimated to different temperatures between 10 and 20 °C also differed in external morphology, but discriminant analysis yielded misclassification rates of 5.3–23.3%.

3. Morphological response to the presence of copepod predators was weaker than that caused by temperature change. Long‐term exposure of clones to copepod predators induced a significant increase in size of appendages in the two species but left body size unaffected. Again, species identification by discriminant functions could be made without any error, whereas conspecific controls and experimentals were misclassified at rates between 19.4 and 29.5%.

4. It is suggested that temperature is the main proximal cue for Bosmina cyclomorphosis. The distinct response to temperature of B. pellucida and B. cornuta may also account for seasonal differences in abundance observed in field.
Genetic and morphological differentiation of Dikerogammarus invaders and their invasion history in Central Europe
Authors: Müller Jakob C. , Schramm Stephanie , Seitz Alfred
Published: March 2003

SUMMARY 1. Biological invasions often involve close taxonomic relatives either as native/invader pairs or as invader/invader pairs. Precise identification and differentiation of species is therefore of paramount importance to reconstruct the invasion history. Genetic studies are indispensable in the case of morphologically conservative taxonomic groups.

2. We analysed the Pontocaspian freshwater amphipods Dikerogammarus that have successfully invaded the benthos of large Central European rivers. Taxonomic uncertainties were clarified by phylogenetic analyses of mitochondrial 16S and COI genes. The three‐way partitioning of allozyme genotypes in a syntopic population further corroborated the taxonomic status of the three species Dikerogammarus haemobaphes, D. villosus and D. bispinosus. Dikerogammarus bispinosus had been prior misidentified as a subspecies of D. villosus. The conspicuous colour types of D. villosus, however, appeared to be conspecific.

3. The genetic identification of the previously more abundant D. haemobaphes individuals in old samples supported the ‘successive invasion wave’ hypothesis with D. haemobaphes as the first invader displaced by the second invader D. villosus. Dikerogammarus bispinosus could be a potential future invader.

4. Haplotype differentiation was apparent between two invasion lines of D. haemobaphes, but the occurrence of a single widespread haplotype indicates genetic impoverishment during rapid colonisation.
Water temperature, light intensity and zooplankton density and the feeding activity of juvenile brook charr (Salvelinus fontinalis)
Authors: Marchand F. , Magnan P. , Boisclair D.
Published: March 2003

SUMMARY 1. The objective of this study was to evaluate the effects of zooplankton biomass (as a measure of density), fish biomass, light intensity and water temperature on the attack rate and swimming characteristics (i.e. swimming speed and angle of turn) of juvenile (1+) brook charr (Salvelinus fontinalis) in field enclosures. We used a portable underwater camera system in a series of pelagic enclosures to quantify the feeding behaviour of brook charr over a gradient of natural conditions.

2. In simple linear or non‐linear regression models we found (i) that attack rate and angle of turn were positively related to water temperature, (ii) that attack rate and swimming speed were positively related to zooplankton biomass and light intensity and (iii) that attack rate was positively related to swimming speed. In multiple regression models, fish biomass, light intensity and variance of the angle of turn accounted for 87% of the variation in attack rate. Light intensity and water temperature accounted for 86% of the variation in swimming speed. Fish gut fullness and attack rate accounted for 83% of the variation in the variance of the angle of turn executed by fish.

3. The increase in the number of attacks as zooplankton biomass increases conforms to the general positive functional response observed in other fish species. Our results also support the hypothesis that swimming speed increases with prey biomass. We did not observe a plateau in attack rate as zooplankton biomass increased. As our experiments were performed under natural biotic and abiotic conditions, factors other than zooplankton biomass might affect or limit this response, such as water temperature and light intensity.

4. Because zooplankton biomass was correlated with water temperature and light intensity, it was not possible to evaluate the independent contribution of these factors on the attack rate and swimming characteristics (swimming speeds and angle of turn) of brook charr. However, this study highlighted the impact of these factors on the feeding behaviour of juvenile brook charr when feeding in the pelagic habitat under natural conditions, and their importance in future models of optimal foraging and fish habitat quality.
Effect of wave exposure on vegetation abundance, richness and depth distribution of shallow water plants in a New Zealand lake
Authors: Riis Tenna , Hawes IAN
Published: March 2003

SUMMARY 1. The effects of physical disturbance in terms of wave exposure, shore slope and substrate mobility on the presence, species richness, cover and depth limits of the low‐growing, shallow water macrophyte community (called the low mixed community) were examined at 41 shore sites in Lake Wanaka, South Island, New Zealand.

2. Wave exposure at a site was described by the previous year's maximum depth of sediment motion and maximum vertical extension of waves, determined from a computer wave model. Shore slope at each site was recorded from −1 to 0 m depth, and sediment stability was assessed as the cover of small gravel.

3. The low mixed community was only present on sites where the previous year's maximum depth of sediment motion was <8 m, maximum wave run‐up was <0.3 m, shore slope <0.12 m m−1, and small gravel cover <78%.

4. Species richness, cover and depth limits of the low mixed community decreased with increasing disturbance on the sites. Sixty‐two percentage of the variation in species richness could be explained by physical disturbance variables when all sites were included (N=41). When only sites with a low mixed community were included (N=22), only 18% of the variation was explained. Species richness within sites supporting a low mixed community is thus poorly explained by physical disturbance, whereas presence or absence is better explained. There was no evidence to support the intermediate disturbance hypothesis in this study.

5. Disturbance as a result of waves explained 86% of the variation in cover among sites with a low mixed community and accounted for 68 and 58% of the variation in upper and lower depth limit of the low mixed community, respectively.

6. The models obtained in this study can be used as predictive models for the low mixed community in New Zealand lakes in relation to natural physical disturbance on the shore. By integrating these results with previous studies on the effect of water level fluctuation, we describe a generalised optimum physical habitat for the low mixed community in New Zealand lakes.
Effects of livestock grazing on benthic invertebrates from a native grassland ecosystem
Authors: Scrimgeour Garry J. , Kendall Sharon
Published: March 2003

SUMMARY 1. The effects of cattle grazing on stream bank stability, biomass of riparian vegetation, instream vegetation cover, biomass of coarse particulate organic matter (CPOM) and epilithon and benthic invertebrate community structure were investigated over a 2‐year period using: (i) enclosures containing different cattle grazing treatments and (ii) by comparing streams with different grazing intensities in the Cypress Hills Provincial Park, Alberta, Canada.

2. Livestock enclosure experiments comprised four treatments of: (1) early season cattle grazing (June–August), (2) late season cattle grazing (August–September), (3) all season cattle grazing (June–September) and (4) cattle‐absent controls. All four treatments were replicated in two streams while two treatments (i.e. cattle‐absent controls, early season cattle grazing) were established in a third stream.

3. Bank stability, estimated visually based on sediment inputs to the stream channel, increased significantly in cattle‐absent treatments compared with cattle‐present enclosures over the 2‐year study period.

4. Epilithic chlorophyll a was significantly affected by time, but neither cattle nor the interaction of time and treatment were significant.

5. At the end of the experiment, total invertebrate biomass in the late and all‐season treatment exceeded that in the early and cattle‐absent treatments. However, excluding cattle from the streams, at any of the different treatments, had little clear impact on the total benthic invertebrate abundance or the abundance of the predominant functional feeding groups over the 2‐year study period.

6. In contrast, comparisons of benthic assemblages from streams with different grazing intensities showed that the non‐grazed reach of Storm Creek contained significantly higher biomass of CPOM and shredders compared with the cattle‐absent enclosures in Battle, Graburn and Nine Mile creeks. Redundancy analysis showed that benthic communities from all enclosures and Storm Creek in summer and autumn 2000 were affected primarily by CPOM biomass, pH, nitrate, turbidity and benthic chlorophyll a. Construction of a 99% probability ellipse from enclosure sites showed that invertebrate communities from livestock enclosures differed from that in the non‐grazed Storm Creek.

7. Results from stream‐scale comparisons indicate that current livestock grazing practices in the Cypress Hills significantly impact riparian zones, stream channels and benthic invertebrate community structure and that alternative practices, such as rotational grazing, need to be developed.
Invasibility of a reservoir to exotic Daphnia lumholtzi: experimental assessment of diet selection and life history responses to cyanobacteria
Authors: Pattinson K. R. , Havel J. E. , Rhodes R. G.
Published: March 2003

SUMMARY 1. In reservoirs of the south‐central United States, the exotic cladoceran Daphnia lumholtzi is common during warm midsummer conditions, when cyanobacteria are abundant and native Daphnia are rare. In the current study, we employed surveys, field experiments, and a life table experiment to investigate the role of food quality in explaining the distribution and phenology of D. lumholtzi, relative to two native species (Daphnia parvula and Daphnia mendotae).

2. During May–September 2000 in eutrophic McDaniel Lake, Missouri U.S.A., cyanobacteria (primarily Oscillatoria) first appeared at 6‐m depth and then became abundant throughout the epilimnion.

3. During the May field experiment, D. lumholtzi, D. parvula and D. mendotae all consumed a similar diet of algae, showing positive selection for small greens (chlorophytes and cryptophytes <20 μm). During the July experiment, when the epilimnion exceeded 25 °C and cyanobacteria were common in the lake, D. lumholtzi consumed significantly more total algae and more cyanobacteria than the two native species. Although the Daphnia selected against cyanobacteria, all three species consumed about 25% of this food in their diet.

4. A life table experiment compared the responses of D. lumholtzi and D. parvula with variation in density of high‐quality food (Ankistrodesmus) and concentration of a toxic strain of cyanobacteria (Anabaena flos‐aquae). Both Daphnia species showed reduced survivorship, fertility and intrinsic rates of increase in response to elevated concentrations of cyanobacteria, particularly at the higher food level.

5. The results suggest that D. lumholtzi shows similar inhibition from cyanobacteria as does the native Daphnia. However, their continued high in situ feeding rates imply that D. lumholtzi is less affected by midsummer conditions in warm‐water reservoirs than are native Daphnia.
Temporal dynamics in epipelic, pelagic and epiphytic algal production in a clear and a turbid shallow lake
Authors: Liboriussen Lone , Jeppesen Erik
Published: March 2003

SUMMARY 1. Pelagic and epipelic microalgal production were measured over a year in a pre‐defined area (depth 0.5 m) in each of two lakes, one turbid and one with clear water. Further estimates of epiphytic production within reed stands were obtained by measuring production of periphyton developed on artificial substrata.

2. Total annual production of phytoplankton and epipelon was 34% greater in the turbid lake (190 g C m−2 year−1) than in the clearwater lake (141 g C m−2 year−1). However, the ratio of total production to mean water column TP concentration was two fold greater in the clearwater lake.

3. Phytoplankton accounted for the majority of the annual production (96%) in the turbid lake, while epipelic microalgal production dominated (77%) in the clear lake. The relative contribution of epipelic algae varied over the year, however, and in the turbid lake was higher in winter (11–25%), when the water was relatively clear, than during summer (0.7–1.7%), when the water was more turbid. In the clearwater lake, the relative contribution of epipelon was high both in winter, when the water was most clear, and in mid‐summer, when phytoplankton production was constrained either by nutrients or grazing.

4. Compared with pelagic and epipelic primary production, epiphytic production within a reed stand was low and did not vary significantly between the lakes.

5. The study supports the theory of a competitive and compensatory trade‐off between primary producers in lakes with contrasting nutrient concentrations, resulting in relatively small differences in overall production between clear and turbid lakes when integrating over the season and over different habitats.
Carbon gains by desiccation‐tolerant plants at elevated CO2
Authors: Tuba Z. , Csintalan Z. , Szente K. , Nagy Z. , Grace J.
Published: March 2003

1. There have been no reports of the long‐term responses of the desiccation‐tolerant (DT) plants to elevated CO2. Xerophyta scabrida is a DT woody shrub, which loses chlorophylls and thylakoids during desiccation: a so‐called poikilochlorophyllous desiccation‐tolerant species (PDT). When the leaves of X. scabria are allowed to desiccate, the species shows many of the normal features of (P)DT plants.

2. However, the duration of photosynthesis in X. scabria is prolonged by 300% when the measurements are made at 700 as opposed to 350p.p.m. CO2. The implication is that the carboxylating enzymes must still have been active at this time to enable appreciable photosynthetic activity. This response could have far‐reaching implications for the success of such species in a future climate.

3. Lichens and mosses, representing the homoiochlorophyllous DTs (HDT), retain their chlorophyll content and photosynthetic apparatus during desiccation. We show the desiccation responses of two common HDT species (Cladonia convoluta and Tortula ruralis) to elevated CO2 for comparison. Both HDT species showed increased net CO2 uptake in the material grown at high CO2 by more than 30% in moss and by more than 50% in lichen. It is concluded that desiccation‐tolerant plants will be among the main beneficiaries of a high CO2 future.
The influence of sex and body size on food habits of a giant tropical snake, Python reticulatus
Authors: Shine R. , Harlow P. S. , Keogh J. S. , Boeadi
Published: March 2003

1. In many animal species, dietary habits shift with body size, and differ between the sexes. However, the intraspecific range of body sizes is usually low, making it difficult to quantify size‐associated trophic shifts, or to determine the degree to which sex differences in diet are due to body‐size differences. Large snakes are ideal for such a study, because they provide a vast range of body sizes within a single population.

2. More than 1000 Reticulated Pythons (Python reticulatus) from southern Sumatra were examined, with specimens from 1·5 to > 6 m in snout–vent length, and from 1 to 75 kg in mass. Females attained much larger body sizes than did conspecific males (maxima of 20 vs 75 kg, 5 vs 7 m), but had similar head lengths at the same body lengths.

3. Prey sizes, feeding frequencies and numbers of stomach parasites (ascarid nematodes) increased with body size in both sexes, and dietary composition changed ontogenetically. Small snakes fed mostly on rats, but shifted to larger mammalian taxa (e.g. pangolins, porcupines, monkeys, wild pigs, mouse deer) at 3–4‐m body length.

4. Adult males and females showed strong ecological divergence. For some traits, this divergence was entirely caused by the strong allometry (combined with sexual size dimorphism), but in other cases (e.g. feeding frequency, dietary composition), the sexes followed different allometric trajectories. For example, females shifted from rats to larger mammals at a smaller body size than did conspecific males, and feeding frequencies increased more rapidly with body size in females than in males. These allometric divergences enhanced the degree of sex difference in trophic ecology induced by sexual size dimorphism.
Female control of the embryonic environment in a terrestrial amphipod, Mysticotalitrus cryptus (Crustacea)
Authors: Morritt D. , Richardson A. M. M.
Published: March 2003

1. In amphipod crustaceans the ventral chamber plays an integral role in a number of physiological processes and in the female forms the marsupium in which eggs are brooded. The ventral chamber can be viewed as a pre‐adaptation to the colonization of land by the family Talitridae. The hypothesis that the female of the terrestrial species, Mysticotalitrus cryptus, can control the osmotic concentration of the marsupial fluid ([MF]) bathing the eggs, thereby buffering the brood from potential physiological stresses presented by the terrestrial environment, is examined.

2.[MF] was maintained significantly higher than the concentration of the external medium ([Medium]) on both dechlorinated tap‐water and 400 mOsm kg–1 media. In each case, [MF] was intermediate to [Medium] and the concentration of the female haemolymph ([Haem]): when [Medium] = 40 mOsm kg–1, [MF] = 277 mOsm kg–1 and [Haem] = 590 mOsm kg–1, respectively, and when [Medium] = 413 mOsm kg–1, [MF] = 516 mOsm kg–1 and [Haem] = 722 mOsm kg–1, respectively.

3. Evidence is provided that females produce urine that is isosmotic with the haemolymph and that the urine is directed, by capillarity, into the marsupium via cuticular channels. It is suggested that this urine plays a role in controlling [MF] in combination with other behavioural mechanisms.

4. Some preliminary observations are presented on the ontogeny of embryonic osmoregulation in M. cryptus which suggest that osmoregulatory ability improves with developmental stage. There is also limited evidence for the ability of the late embryonic stages to hypo‐osmoregulate on concentrated media, even though adults lack this capacity.

5. The results are discussed in relation to the colonization of the terrestrial environment by the Talitridae.
Effect of nectar‐robbing birds on fruit set of Fuchsia magellanica in Tierra Del Fuego: a disrupted mutualism
Authors: Traveset A. , Willson M. F. , Sabag C.
Published: March 2003

1. This paper investigates spatial habitat variation in flower visitation by avian pollinators (mainly Hummingbirds) and nectar robbers to Fuchsia magellanica at the southern limit of its range, Tierra del Fuego, and their effects on plant reproductive success.

2. The plant‐pollination mutualism appears to be disrupted as Hummingbirds (Sephanoides galeritus) are rare at this high latitude and the frequencies of a nectar‐robbing bird (Phrygilus patagonicus) are high, especially in open areas where F. magellanica is most abundant.

3. Nectar robbery by P. patagonicus reduced fruit set about 20%, mainly because this fringillid can damage the ovary when piercing a flower. This bird was more abundant in open areas than inside the forest and, as expected, flower piercing was also more frequent in the former habitat.

4. Spatial variation was also found in the frequency of flower visitation by Hummingbirds; these birds foraged chiefly in the forest presumably because of the greater probability of finding intact (non‐robbed) flowers there. This suggests that cross‐pollinations in this self‐compatible plant are more likely to occur in the forest. Nectar robbers therefore may influence not only the quantity of seeds produced but also, indirectly, their quality.

5.
Fuchsia magellanica is polymorphic in flower colour. Robbery was significantly lower in the pale than in the normal (red) morph, although fruit set was similar between morphs.