bluuebunny/crossref_metadata_2025 huggingface dataset:
Activity profiles of bacterioplankton in a eutrophic river
Authors: Sinsabaugh  , Foreman
Published: March 2003

1. The significance of microbial diversity in processing dissolved organic matter (DOM) is largely unknown. We investigated the range of functional diversity in the bacterioplankton from a eutrophic river by profiling extracellular enzyme activities (EEA) and substrate‐induced respiration (SIR) patterns.

2. The EEA profiles consisted of assays for 21 hydrolases, measured using fluorogenic substrates arrayed on 96‐well microplates. Commercially available BiOLOG® GN and ECO plates, which contained 120 different substrates, were used for the SIR profiles.

3. The EEA data were more dynamic than the SIR. Five enzymes, leucine aminopeptidase, alkaline phosphatase, alanine aminopeptidase, arginine aminopeptidase and β‐glucosidase, showed consistently high activity; ten others were ubiquitous at lower activity levels; the remainder were detected intermittently. The SIR data showed less temporal variability. With one exception (citrate), the 20 substrates that generated the largest responses were all saccharides or their derivatives.

4. The EEA and SIR data did not generally correlate. Both methods were effective for ordinating bacterioplankton although, unlike the SIR, the EEA ordination followed a clear temporal trajectory.

5. Because the SIR profiles are based on a culture response, whilst the EEA profiles measure activity of the extant community, the latter appear to be more directly linked to the mechanics of DOM processing.
Chironomid‐based inference models for estimating end‐of‐summer hypolimnetic oxygen from south‐central Ontario shield lakes
Authors: Quinlan Roberto , Smol John P.
Published: March 2003

1. Subfossil chironomid head capsules were sampled from surficial sediments from 86 boreal shield lakes in south‐central Ontario, Canada. Lake characteristics ranged from shallow to very deep (> 80 m), ultraoligotrophic to mesotrophic, and with end‐of‐summer hypolimnetic oxygen conditions ranging from near‐saturation to anoxic.

2. Subfossil chironomid assemblages, comprising 44 taxa from 59 lakes, were analysed using multivariate ordination techniques such as redundancy analysis (RDA) and canonical correspondence analysis (CCA). Forward selection in RDA and CCA both showed that measures of oxygen, such as end‐of‐summer volume‐weighted hypolimnetic oxygen concentration (VWHO) and bottom oxygen concentration (botO2), were the strongest explanatory variables for the chironomid data. Maximum depth and major ion chemistry were also important explanatory variables.

3. Oxygen inference models were developed using partial‐least‐squares regression (PLS), weighted‐averaging partial‐least‐squares regression (WA‐PLS), and weighted averaging regression (WA). Models were developed using both the full 44 taxa assemblage (which included littoral taxa) and using only 15 profundal‐type taxa.

4. Cross‐validated models (jackknifing) using full‐assemblage or profundal‐only taxa had similar statistical power (similar root mean squared error of prediction, RMSEP). The best models had moderate predictive power, with an r2jack as high as 0.56, and an RMSEP as low as 2.15 mg L–1 for [VWHO], and an r2jack of 0.49 and an RMSEP of 0.24 for log([botO2] + 1).

5. Reconstruction of [VWHO] and [botO2] using a previously published chironomid profile that showed strong lake response to land‐clearance and logging suggests that oxygen inference models are reliable and accurate, reflecting the qualitative changes occurring in subfossil assemblages. However, the profundal‐only models may be misleading in situations where the ratio of littoral‐to‐profundal subfossils changes drastically in response to lake disturbance.
Inter‐biome comparison of factors controlling stream metabolism
Authors: Mulholland P. J. , Fellows C. S. , Tank J. L. , Grimm N. B. , Webster J. R. , Hamilton S. K. , Martí E. , Ashkenas L. , Bowden W. B. , Dodds W. K. , Mcdowell W. H. , Paul M. J. , Peterson B. J.
Published: March 2003

1. We studied whole‐ecosystem metabolism in eight streams from several biomes in North America to identify controls on the rate of stream metabolism over a large geographic range. The streams studied had climates ranging from tropical to cool‐temperate and from humid to arid and were all relatively uninfluenced by human disturbances.

2. Rates of gross primary production (GPP), ecosystem respiration (R) and net ecosystem production (NEP) were determined using the open‐system, two‐station diurnal oxygen change method.

3. Three general patterns in metabolism were evident among streams: (1) relatively high GPP with positive NEP (i.e. net oxygen production) in early afternoon, (2) moderate primary production with a distinct peak in GPP during daylight but negative NEP at all times and (3) little or no evidence of GPP during daylight and a relatively constant and negative NEP over the entire day.

4. Gross primary production was most strongly correlated with photosynthetically active radiation (PAR). A multiple regression model that included log PAR and stream water soluble reactive phosphorus (SRP) concentration explained 90% of the variation in log GPP.

5. Ecosystem respiration was significantly correlated with SRP concentration and size of the transient storage zone and, together, these factors explained 73% of the variation in R. The rate of R was poorly correlated with the rate of GPP.

6. Net ecosystem production was significantly correlated only with PAR, with 53% of the variation in log NEP explained by log PAR. Only Sycamore Creek, a desert stream in Arizona, had positive NEP (GPP: R > 1), supporting the idea that streams are generally net sinks rather than net sources of organic matter.

7. Our results suggest that light, phosphorus concentration and channel hydraulics are important controls on the rate of ecosystem metabolism in streams over very extensive geographic areas.
Physico‐chemistry and aquatic insects of a glacier‐fed and a spring‐fed alpine stream
Authors: Füreder Leopold , Schütz Cornelia , Wallinger Manfred , Burger Rainer
Published: March 2003

1. Physico‐chemical conditions and benthic macroinvertebrates were studied in two adjacent alpine streams in the Tyrolean Alps, Austria, for 2 years, and aquatic insect emergence was recorded for 1 year.

2. In the spring‐fed system, maximum discharge and increased concentrations of suspended solids, nitrate and particulate phosphorus occurred during snowmelt in June. In the glacier‐fed stream, high discharge and strong diel fluctuations in flow and concentrations of suspended solids created a harsh and unstable environment during summer. Glacial ablation, variation in groundwater inflow, and water inputs from tributaries draining calcareous rocks caused water chemistry to vary both seasonally and longitudinally in glacier‐fed Rotmoosache.

3. A total of 126 aquatic or semi‐aquatic invertebrate taxa were collected, 94 of which were found in the glacier‐fed stream and 120 in the spring‐fed stream. Chironomid abundance was 2–8 times and taxa richness 2–3 times lower in the glacier‐fed stream than in the spring‐fed stream, as was the number of chironomid taxa (72 versus 93 total).

4. These results broadly support the conceptual model by Milner & Petts (1994) concerning glacier‐fed stream systems. However, single samples and seasonal means showed relatively high invertebrate abundance and richness, especially during winter, indicating a considerable degree of spatial and temporal variability.

5. We suggest that the seasonal shifts from harsh environmental conditions in summer to less severe conditions in autumn and a rather constant environment in winter are an important factor affecting larval development, life‐history patterns and the maintenance of relatively high levels of diversity and productivity in glacier‐fed streams.
Carry‐over effects of embryonic acid conditions on development and growth ofRana temporariatadpoles
Authors: RÄsänen K. , Laurila A. , Merilä J.
Published: March 2003

1. Conditions experienced during the early stages of development may have carry‐over effects on performance during later life. The egg laying period and embryonic development of temperate and boreal zone amphibians often coincides with peak acidity resulting from spring snow‐melt, but the effects of acid conditions during embryonic stage on subsequent performance are unknown.

2. We investigated the potential carry‐over effects of acidity during the embryonic stage on performance up to metamorphosis in the common frog (Rana temporaria) tadpoles. There were four combinations of acid (4.5) and neutral (7.5) pH treatments applied to the egg and larval stages in a factorial laboratory experiment. In addition, we studied the difference in embryonic and larval tolerance of acidity between two populations originating from circumneutral (pH 6.6) and acidic conditions (pH 4.8).

3. The effects of acid conditions during the embryonic stage were sublethal, as indicated by delayed development and reduced size. Under acid conditions, tadpoles that had been raised in neutral water as embryos at first grew more slowly than tadpoles raised under acid conditions as embryos. At metamorphosis, no effects of embryonic acidity were detectable indicating that tadpoles were able to compensate fully for the initial reduction in growth.

4. Acid conditions during the larval period had a strongly negative effect on survival, size and age at metamorphosis. The amount of food consumed was lower under acid conditions, suggesting that reduced food consumption was at least partly responsible for the negative effects.

5. Although the two populations differed in the length of larval period, there was no indication of a differential response to the treatments in any of the metamorphic traits studied.

6. These results suggest that, although moderate acid conditions during embryonic development affect growth and development negatively, this influence does not persist after conditions have returned to normal. However, even moderately acid conditions during the larval period may have a strong negative influence on survival and performance of the tadpoles.
Population genetic structure of two water strider species in the Ecuadorian Amazon
Authors: GALACATOS KATERINA , COGNATO ANTHONY I. , SPERLING FELIX A. H.
Published: March 2003

1. We used mtDNA sequence variation to estimate population genetic structure between and among water strider populations ofPotamobates williamsiandP.sumacoin the Ecuadorian Amazon.

2. Sequencing of the COI mitochondrial gene revealed 16 haplotypes, which were summarised into four haplotype groups.P.williamsiandP.sumacoshared two common and widespread haplotypes.

3. Population structure was moderate and gene flow was low. Both air and river distances were significantly correlated with gene flow and, thus, indicative of isolation by distance.

4. The genetic structure within and among populations ofP. williamsiandP. sumacowas probably not influenced by the dynamic tropical lotic system.
Dispersal of aquatic organisms by waterbirds: a review of past research and priorities for future studies
Authors: FIGUEROLA JORDI , GREEN ANDY J.
Published: March 2003

1. Inland wetlands constitute ecological islands of aquatic habitat often isolated by huge areas of non‐suitable terrestrial habitats. Although most aquatic organisms lack the capacity to disperse by themselves to neighbouring catchments, many species present widespread distributions consistent with frequent dispersal by migratory waterbirds.

2. A literature review indicates that bird‐mediated passive transport of propagules of aquatic invertebrates and plants is a frequent process in the field, at least at a local scale. Both endozoochory (internal transport) and ectozoochory (external transport) are important processes.

3. The characteristics of the dispersed and the disperser species that facilitate such transport remain largely uninvestigated, but a small propagule size tends to favour dispersal by both internal and external transport.

4. We review the information currently available on the processes of waterbird‐mediated dispersal, establishing the limits of current knowledge and highlighting problems with research methods used in previous studies. We also identify studies required in the future to further our understanding of the role of such dispersal in aquatic ecology.
Biodiversity and resource use of larval chironomids in relation to environmental factors in a large river
Authors: FESL CHRISTIAN
Published: March 2003

1. Larval chironomids were examined at four sites on a cross‐section of the River Danube in Austria between September 1995 and August 1996. The sites differed in hydraulics, sediment composition and habitat stability.

2. Species–accumulation curves, showing the increase in number of species with increasing sampling effort, from three main channel sites were best described by a logarithmic model, suggesting that most of the species occurring at these sites were found. Data from a site connected to a backwater fitted best to a power model, indicating a random assemblage with additional species immigrating from the backwater area.

3. Properties of the community were estimated using Jackknife techniques: species richness (range of mean values at the four sites: 32–91), H′ diversity (1.5–2.3), evenness (0.23–0.28), spatial resource width (0.01–0.06), spatial resource overlap (0.13–0.20), spatial species aggregation (0.60–0.77), temporal community persistence (Kendal's correlation coefficient: 0.47–0.60) and beta‐diversity (6.2–9.7).

4. Redundancy analysis (RDA) was used to relate the community properties and species abundance to environmental factors. Habitat stability was the major factor associated with community structure. Higher sediment turnover led to higher spatial aggregation and, consequently, a decrease in spatial resource width and overlap, and to a decline in larval density and species richness.

5. Species‐abundance patterns agreed well with the log‐normal model. Moderate community persistence and stability of the streambed sediments suggest that the log‐normal model may be a good descriptor for communities of intermediately disturbed habitats, like large rivers, rather than stable habitats.
Terrestrial invertebrates inhabiting lowland river floodplains of Central Amazonia and Central Europe: a review
Authors: ADIS JOACHIM , JUNK WOLFGANG J.
Published: March 2003

1. Amazonian terrestrial invertebrates produce high population densities during favourable periods and may suffer a drastic decrease during occasional floods and droughts. However, the monomodal, predictable flood pulse of the larger Amazonian rivers favours the development of morphological (respiratory organs, wing‐dimorphism), phenological (synchronization of life cycles, univoltine mode of life), physiological (flooding ability, gonad dormancy, alternating number of developmental stages), and behavioural adaptations (migration, temporal diving) with numerous interactions.

2. In lowlands of Central Europe, the flood pulse of large rivers is less predictable than in Central Amazonia and is superimposed by the seasonal light/temperature pulse (summer/winter regime). Some terrestrial invertebrates show physiological resistance against inundation or drought, phenologies fitting the normal annual rhythm of water level fluctuation (quiescence or diapause of eggs or adult invertebrates), high dispersal ability and migration. However, most species survive simply using a `risk strategy', combining high reproduction rates, dispersal and reimmigration following catastrophic events.

3. The diversity of species in terrestrial invertebrates is lower in lowland riverine ecosystems of Central Amazonia and Central Europe compared with the respective uplands because of flood stress in these systems. However, floodplains in Central Amazonia possess a greater number of endemic species in comparison with Central European floodplains because of long periods of fairly stable climatic conditions in comparison with large palaeoclimatic changes in Central Europe.
A landscape perspective of surface–subsurface hydrological exchanges in river corridors
Authors: MALARD FLORIAN , TOCKNER KLEMENT , DOLE‐OLIVIER MARIE‐JOSÉ , WARD J. V.
Published: March 2003

1.  River corridors can be visualised as a three‐dimensional mosaic of surface–subsurface exchange patches over multiple spatial scales. Along major flow paths, surface water downwells into the sediment, travels for some distance beneath or along the stream, eventually mixes with ground water, and then returns to the stream.

2.  Spatial variations in bed topography and sediment permeability result in a mosaic of patch types (e.g. gravel versus sandy patches) that differ in their hydrological exchange rate with the surface stream. Biogeochemical processes and invertebrate assemblages vary among patch types as a function of the flux of advected channel water that determines the supply of organic matter and terminal electron acceptors.

3.  The overall effect of surface–subsurface hydrological exchanges on nutrient cycling and biodiversity in streams not only depends on the proportion of the different patch types, but also on the frequency distribution of patch size and shape.

4.  Because nutrients are essentially produced or depleted at the downwelling end of hyporheic flow paths, reach‐scale processing rates of nutrients should be greater in stretches with many small patches (e.g. short compact gravel bars) than in stretches with only a few large patches (e.g. large gravel bars).

5.  Based on data from the Rhône River, we predict that a reach with many small bars should offer more hyporheic refugia for epigean fauna than a reach containing only a few large gravel bars because benthic organisms accumulate preferentially in sediments located at the upstream and downwelling edge of bars during floods. However, large bars are more stable and may provide the only refugia during severe flood events.

6.  In river floodplain systems exhibiting pronounced expansion/contraction cycles, hyporheic assemblages within newly created patches not only depend on the intrinsic characteristics of these patches but also on their life span, hydrological connection with neighbouring patches, and movement patterns of organisms.

7.  Empirical and theoretical evidence illustrate how the spatial arrangement of surface–subsurface exchange patches affects heterogeneity in stream nutrient concentration, surface water temperature, and colonisation of dry reaches by invertebrates.

8.  Interactions between fluvial action and geomorphic features, resulting from seasonal and episodic flow pulses, alter surface–subsurface exchange pathways and repeatedly modify the configuration of the mosaic, thereby altering the contribution of the hyporheic zone to nutrient transformation and biodiversity in river corridors.
Large wood and fluvial processes
Authors: GURNELL A. M. , PIÉGAY H. , SWANSON F. J. , GREGORY S. V.
Published: March 2003

1. Large wood forms an important component of woodland river ecosystems. The relationship between large wood and the physical characteristics of river systems varies greatly with changes in the tree species of the marginal woodland, the climatic and hydrological regime, the fluvial geomorphological setting and the river and woodland management context.

2. Research on large wood and fluvial processes over the last 25 years has focussed on three main themes: the effects of wood on flow hydraulics; on the transfer of mineral and organic sediment; and on the geomorphology of river channels.

3. Analogies between wood and mineral sediment transfer processes (supply, mobility and river characteristics that affect retention) are found useful as a framework for synthesising current knowledge on large wood in rivers.

4. An important property of wood is its size when scaled to the size of the river channel. ′Small′ channels are defined as those whose width is less than the majority of wood pieces (e.g. width < median wood piece length). `Medium' channels have widths greater than the size of most wood pieces (e.g. width < upper quartile wood piece length), and `Large' channels are wider than the length of all of the wood pieces delivered to them.

5. A conceptual framework defined here for evaluating the storage and dynamics of wood in rivers ranks the relative importance of hydrological characteristics (flow regime, sediment transport regime), wood characteristics (piece size, buoyancy, morphological complexity) and geomorphological characteristics (channel width, geomorphological style) in `Small', `Medium' and `Large' rivers.

6. Wood pieces are large in comparison with river size in `small' rivers, therefore they tend to remain close to where they are delivered to the river and provide important structures in the stream, controlling rather than responding to the hydrological and sediment transfer characteristics of the river.

7. For `Medium' rivers, the combination of wood length and form becomes critical to the stability of wood within the channel. Wood accumulations form as a result of smaller or more mobile wood pieces accumulating behind key pieces. Wood transport is governed mainly by the flow regime and the buoyancy of the wood. Even quite large wood pieces may require partial burial to give them stability, so enhancing the importance of the sediment transport regime.

8. Wood dynamics in `Large' rivers vary with the geometry of the channel (slope and channel pattern), which controls the delivery, mobility and breakage of wood, and also the characteristics of the riparian zone, from where the greatest volume of wood is introduced. Wood retention depends on the channel pattern and the distribution of flow velocity. A large amount is stored at the channel margins. The greater the contact between the active channel and the forested floodplain and islands, the greater the quantity of wood that is stored.
Life history of Daphnia galeata in a hypertrophic reservoir and consequences of non‐consumptive mortality for the initiation of a midsummer decline
Authors: Hülsmann S. , Voigt H.
Published: March 2003

SUMMARY 1. Field and laboratory investigations were combined in a 2‐year study on the initiation of a midsummer decline of Daphnia galeata Sars in a hypertrophic reservoir. Quantitative field samples were taken twice a week, and, adult and juvenile mortality rates were calculated. Patterns of reproduction and survival of daphnids born during spring and early summer under fluctuating food conditions were determined in life‐table experiments.

2. The abundance of Daphnia increased strongly in early May and declined in June 1998 (midsummer decline). In 1999, Daphnia density increased only slowly in spring and remained constantly high throughout the summer.

3. Food conditions (concentrations of POC<30 μm) for daphnids deteriorated in both years in response to increasing Daphnia densities, resulting in a clear‐water phase of about 4 weeks. When Daphnia abundance declined in 1998, POC<30 μm concentrations increased greatly, whereas in 1999 food conditions improved only slightly and Secchi depth remained high.

4. Survival of daphnids in life‐table experiments decreased greatly after food became rare and was strongly reduced in those animals born during the clear‐water phase compared with those born later. In addition, age at first reproduction was retarded during the clear‐water phase, resulting in very low population growth rates. Survivorship patterns in life‐table experiments suggest a strong impact of non‐consumptive mortality on Daphnia population dynamics.

5. Field data of mortality point to differences in mortality patterns between years, probably resulting from different predation impacts of juvenile fish. In both years, however, adult mortality contributed substantially to overall mortality at the end of the clear‐water phase. As bottom‐up effects on D. galeata were very similar in both years, the significance of non‐consumptive mortality on the initiation of midsummer declines appears to depend largely on recruitment patterns before the clear‐water phase. A high impact can be expected when Daphnia populations are dominated by a peak cohort of nearly identical age during the clear‐water phase.
Migratory Atlantic salmon as vectors for the transfer of energy and nutrients between freshwater and marine environments
Authors: Jonsson Bror , Jonsson Nina
Published: March 2003

SUMMARY 1. Annual energy, carbon, nitrogen and phosphorus fluxes across the river mouth by Atlantic salmon were estimated for 18 years (1976–94) in the Norwegian River Imsa. The total energy content of the emigrating smolts in each year varied considerably with a mean value of 237 × 103 kJ. That of returning adults also varied between years with a mean value of 141 × 104 kJ. One‐sea‐winter salmon (grilse) made up 65% of the total energy content of the spawners in the river. Dead carcasses remaining in the river after spawning were estimated to have a mean annual energy content of 175 × 103 kJ.

2. The net annual energy flux from the sea to the river varied between 48 × 103 kJ (1987) and 152 × 104 kJ (1989) with a mean of 616 × 103 kJ, and a coefficient of variation of 67%. Average net marine import of the returning adults was 83 × 104 kJ year−1 with a coefficient of variation of 52%. Mean annual export of C, N and P to sea by the smolts was 595, 131 and 22 kg, and by kelts 1535, 352 and 70 kg, respectively, whereas gross import via the adults was 3176 kg C, 735 kg N and 132 kg P. The annual flux across the river mouth was 1046 kg C, 253 kg N and 39 kg P. The net marine import were 1585 kg C, 371 kg N and 60 kg P. The net flux was estimated at 0.2% for nitrogen and 5% for phosphorus of the total river load.

3. The energy flux caused by Atlantic salmon spawning in the River Imsa was relatively high because the general nutrient load in the river is low. Thus, even though most Atlantic salmon survive spawning, their contribution to the nutrient flux in the river is significant.
Effects of stream phosphorus levels on microbial respiration
Authors: Ramírez Alonso , Pringle Catherine M. , Molina Luisenrique
Published: March 2003

SUMMARY 1. We examined microbial respiration among streams in lowland Costa Rica comprising a natural phosphorus gradient (5–350 μg SRP L−1) resulting from variable inputs of solute‐rich (e.g. P, SO4 and Cl) groundwater.

2. Microbial respiration rates were determined by measuring oxygen change in situ in nine low‐order streams on three substrate types: mixed leaves collected from the stream bottom, conditioned Ficus leaves and sediments.

3. Respiration rates on both leaf types were positively related to phosphorus and negatively related to N : P ratios. Microbial respiration rates on sediments were not related to any of the variables [i.e. soluble reactive phosphorus (SRP), N‐NO3 and N : P] measured.

4. Respiration rates on newly colonised Ficus leaves formed an asymptotic curve increasing to a plateau, suggesting that saturation with phosphorus occurred at concentrations <15 μg SRP L−1.

5. To test the hypothesis that phosphorus was the main solute in solute‐rich water that was driving observed differences in microbial respiration rates, we artificially enriched a small stream with phosphorus and measured changes in respiration before and after enrichment.

6. Experimental phosphorus enrichment produced increases in respiration rates similar in magnitude to those observed in the nine streams forming the natural phosphorus gradient, supporting our hypothesis that phosphorus was the major variable driving interstream differences in microbial respiration rates. Respiration rates were higher in this study than those reported for most other tropical streams and rivers with the exception of those reported for tropical Asian streams.

7. Results indicate that variations in phosphorus concentrations can potentially affect patterns of microbial respiration rates at a landscape level via differential inputs of solute‐rich groundwater into streams.
Sex and outcrossing in a sessile freshwater invertebrate
Authors: Freeland Joanna R. , Lodge Rebecca J. , Okamura Beth
Published: March 2003

SUMMARY 1. The freshwater bryozoan Cristatella mucedo, in common with other sessile, benthic freshwater taxa, has an unusual life history: sex occurs during a relatively brief period near the start of the growing season, and overwintering occurs in the form of asexually produced dormant propagules (statoblasts). Consistent observed heterozygosity (Ho) deficits in C. mucedo populations have previously suggested that inbreeding is common, although a possible contribution of a Wahlund effect to low Ho could not be discounted.

2. We have used microsatellite data in the first study based on codominant markers to genetically characterise maternal colonies and larval offspring of C. mucedo. The ‘population’ represented by the larvae was in Hardy–Weinberg equilibrium, which has previously been found in only one of 39 populations of C. mucedo. At least 64% of larvae were the products of outcrossing. We suggest that the unusual early timing of sex may be a strategy to maximise rates of outcrossing within populations of sessile freshwater invertebrates.
Vulnerability of cladoceran species to predation by the copepod Mesocyclops leuckarti: laboratory observations on the behavioural interactions between predator and prey
Authors: Chang Kwang‐Hyeon , Hanazato Takayuki
Published: March 2003

SUMMARY 1. We analysed the vulnerability of a number of cladoceran species (Bosmina longirostris, B. fatalis, Diaphanosoma brachyurum, Ceriodaphnia reticulata, Daphnia ambigua and D. pulex) to predation by Mesocyclops leuckarti in the laboratory.

2. The prey species represented a wide range of body size, morphology, and swimming behaviour. To compare vulnerability, we measured the efficiency of capture and ingestion of each prey species by Mesocyclops. We also measured the rate at which prey were damaged in attacks by Mesocyclops.

3. Mesocyclops preyed effectively on Diaphanosoma and small juvenile Ceriodaphnia but not on Bosmina or Daphnia. Observations suggested that various defence mechanisms, including protruding structures and swimming behaviour and speed, are important in determining prey vulnerability.

4. The body size of Daphnia and Ceriodaphnia seems to be important, because larger animals were better able to escape Mesocyclops attacks. Attacks by Mesocyclops often caused fatal damage, however, even to large Daphnia.
Greenhouse gas dynamics in boreal, littoral sediments under raised CO2 and nitrogen supply
Authors: Liikanen Anu , Ratilainen Eeva , Saarnio Sanna , Alm Jukka , Martikainen Pertti J. , Silvola Jouko
Published: March 2003

SUMMARY 1. The effects of increasing CO2 and nitrogen loading and of a change in water table and temperature on littoral CH4, N2O and CO2 fluxes were studied in a glasshouse experiment with intact sediment cores including vegetation (mainly sedges), taken from a boreal eutrophic lake in Finland. Sediments with the water table held at a level of 0 or at −15 cm were incubated in an atmosphere of 360 or 720 p.p.m. CO2 for 18 weeks. The experiment included fertilisation with NO3– and NH4+ (to a total 3 g N m−2).

2. Changes in the water table and temperature strongly regulated sediment CH4 and cCO2 fluxes (community CO2 release), but did not affect N2O emissions. Increase in the water table increased CH4 emissions but reduced cCO2 release, while increase in temperature increased emissions of both CO2 and CH4.

3. The raised CO2 increased carbon turnover in the sediments, such that cCO2 release was increased by 16–26%. However, CH4 fluxes were not significantly affected by raised CO2, although CH4 production potential (at 22 °C) of the sediments incubated at high CO2 was increased. In the boreal region, littoral CH4 production is more likely to be limited by temperature than by the availability of carbon. Raised CO2 did not affect N2O production by denitrification, indicating that this process was not carbon limited.

4. A low availability of NO3– did severely limit N2O production. The NO3– addition caused up to a 100‐fold increase in the fluxes of N2O. The NH4+ addition did not increase N2O fluxes, indicating low nitrification capacity in the sediments.
Resource availability and population size in cactophilicDrosophila
Authors: Breitmeyer C. M. , Markow T. A.
Published: March 2003

1.Four species ofDrosophila, Drosophila nigrospiracula(Patterson & Wheeler 1942), Drosophila mettleri(Heed 1977), Drosophila pachea(Patterson & Wheeler 1942),andDrosophila mojavensis(Patterson & Crow 1940),are endemic to the Sonoran Desert of North America and breed in different species of necrotic columnar cacti. Differences in resource availability have been suggested to explain the interspecific variability in fly population biology, but resource availability for these species has not been quantitatively assessed thoroughly in either spatial or temporal terms. The resource availability was quantified quarterly at three sites for 3 years and population sizes for eachDrosophilaspecies were estimated.

2.Spatial and temporal availability of resources differed significantly among species of host cacti, with organpipe cactus (Stenocereus thurberi) being the least abundant and senita (Lophocereus schottii) the most abundant spatially.

3.Drosophilaspecies differed significantly in population size. The largest population sizes were found forD. nigrospiraculaandD. mojavensisand smallest forD. pachea. Populations ofD. mettleriwere intermediate to these.

4.Population size was greatest for fly species utilizing host species having the largest and longest lasting necroses.

5.Resource availability does not explain the reduction of fly populations in the summer. Necroses were most abundant when flies were absent.
Implications of shoot structure on the rate of photosynthesis at different levels in a coniferous canopy using a model incorporating grouping and penumbra
Authors: Stenberg P.
Published: March 2003

1. The connection between high leaf area index (LAI) and photosynthetic production with two attributes of coniferous canopy structure: small leaf size and grouping of needles on shoots, was analysed using a simulation model.

2. The small size of conifer needles gives rise to penumbras, which even out the distribution of direct sunlight on the leaf area and thereby act to increase the rate of canopy photosynthesis per unit of LAI.

3. Grouping, by producing a non‐uniform distribution of leaf area, causes a decrease in total canopy light interception at any given LAI, but improves the photosynthetic light capture by shoots in the lower canopy.

4. Application of the model on a case study showed that: (a) grouping had a negative effect on the rate of photosynthesis in the upper canopy, but deeper down in the canopy the situation was reversed; (b) in the lower canopy, photosynthetic rates were up to 10 times higher as a result from the combined effect of grouping and penumbra; (c) grouping did not improve the rate of canopy photosynthesis per unit of LAI, however, it can have a positive effect on the total photosynthetic production by allowing a higher productive LAI to be maintained; (d) penumbra, on the other hand, increased the rate of canopy photosynthesis by as much as 40% for moderate values of the LAI.
Experimental testing of dynamic energy budget models
Authors: Noonburg E. G. , Nisbet R. M. , Mccauley E. , Gurney W. S. C. , Murdoch W. W. , DE Roos A. M.
Published: March 2003

1. Dynamic energy budget (DEB) models describing the allocation of assimilate to the competing processes of growth, reproduction and maintenance in individual organisms have been applied to a variety of species with some success. There are two contrasting model formulations based on dynamic allocation rules that have been widely used (net production and net assimilation formulations). However, the predictions of these two classes of DEB models are not easily distinguished on the basis of simple growth and fecundity data.

2. It is shown that different assumptions incorporated in the rules determining allocation to growth and reproduction in two classes of commonly applied DEB models predict qualitatively distinct patterns for an easily measured variable, cumulative reproduction by the time an individual reaches an arbitrary size.

3. A comparison with experimental data from Daphnia pulex reveals that, in their simplest form, neither model predicts the observed qualitative pattern of reproduction, despite the fact that both formulations capture basic growth features.

4. An examination of more elaborate versions of the two models, in which the allocation rules are modified to account for brief periods of starvation experienced in the laboratory cultures, reveals that a version of the net production model can predict the qualitative pattern seen for cumulative eggs as a function of mass in D. pulex. The analysis leads to new predictions which can be easily tested with further laboratory experiments.
The phenology of gender in homogamous flowers: temporal change in the residual sex function of flowers of Oil‐seed Rape (Brassica napus)
Authors: Bell S. A. , Cresswell J. E.
Published: March 2003

1. We investigated the phenology of the male and female sexual functions in flowers of Oil‐seed Rape (Brassica napus) that were exposed to pollinators in an experimental garden. The female ‘residual sex function’ (RSF) of flowers was measured by hand‐pollinating with genetically marked pollen in order to determine the proportion of ovules that remained available for fertilization by incoming pollen. Male RSF was measured by estimating the proportion of pollen grains that remained in dehiscing anthers.

2. Following flower opening, an average flower’s male and female sexual functions each required for completion c. 13 h of exposure to pollinators. One hour after opening, c. 50% of a flower’s ovules were unavailable to incoming pollen whereas only c. 10% of pollen was removed. Therefore, a flower’s sexual function was predominantly female for the first hour and predominantly male thereafter.

3. We found a fairly close correspondence between the proportion of the stigma covered with pollen and the depletion of female RSF.

4. On average, floral senescence occurred after c. 14·5 h of exposure to pollinators. Our observations are fairly consistent with a simple, economic model of optimal senescence time because the flowers remained open for approximately the same length of time as was necessary for the completion of their sexual functions.

5. A flower’s senescence was hastened when pollen was removed from the anthers, but not when pollen was deposited on the stigma.

6. When flowers were either left undisturbed or hand‐pollinated, senescence occurred after c. 24 h. Pollen removal caused senescence after c. 13 h, which also approximated the longevity of flowers in the experimental garden. Apparently, pollen removal governed floral longevity under field conditions.
The use of variance in enzyme activity as an indicator of long‐term exposure to toxicant‐stressed environments inCulex pipiensmosquitoes
Authors: Callaghan A. , Parker P. J. A. N. , Holloway G. J.
Published: March 2003

1.The identification of easy to use and cheap biomarkers is important as a means of determining whether animals are developing under stressful environmental conditions. Previous studies have indicated that the variance about the mean esterase activity in toxic environments increases in the absence of a significant shift in the mean value, suggesting that variance levels may have potential as a biomarker of toxicant‐stressed or otherwise stressful environments.

2.Several field and laboratory populations of the mosquito,Culex pipiens, were examined for esterase activities using a colorimetric assay and levels of polymorphism using polyacrylamide gel electrophoresis. Some of these populations had been exposed to environmental toxicants (organophosphorus (OP) insecticides).

3.The OP‐stressed field population had lower levels of polymorphism as indicated by fewer electromorphs than the populations that had not been exposed to OPs. However, the mean level of esterase activity was higher in the OP‐stressed populations.

4.Despite having lower genetic variation, the OP‐stressed populations showed much higher levels of variation about the mean enzyme activity, at least two orders of magnitude higher, than the unstressed populations. Knowledge of the genetics of OP resistance in these populations confirmed that the increase in variance was not due to the general switching on of genes in response to stress.

5.One field population that had been exposed to heavy metal pollution had similar levels of esterase activity and variation about the mean as the unstressed populations, suggesting that variation only increases in characters directly affected by the environmental pollutant.

6.The probable factors causing the increase in variance and the potential of this type of variation as a biomarker of stressful environments are discussed.
The photosynthetic drought physiology of a diverse group of southern hemisphere conifer species is correlated with minimum seasonal rainfall
Authors: Brodribb T. , Hill R. S.
Published: March 2003

1. The instantaneous and integrated leaf gas exchange of 13 species of southern hemisphere conifers grown under identical glasshouse conditions were examined to determine whether there was any correlation between the characteristics of water use at the leaf level and environmental water availability.

2. In the conifer species examined, the minimum ratio of internal to ambient CO2 measured in leaves during artificially imposed drought [(ci/ca)min] was strongly correlated with the minimum rainfall observed within the natural range of each species. This suggests that the distributions of these species are constrained by the drought tolerance of their photosynthetic apparatus.

3. A good correlation was found between the ratio of internal to ambient CO2 measured in leaves under optimal conditions (ci/ca)max and leaf δ13C (and hence inferred ∫[ci/ca]). Neither of these, however, correlated with the environmental parameters considered most likely to be limiting species distribution, i.e. precipitation and altitude.

4. These data suggest that decreasing water availability may have been the major factor responsible for the restriction and extinction of conifers in the southern hemisphere.
Seed size and shape are not related to persistence in soil in Australia in the same way as in Britain
Authors: Leishman M. R. , Westoby M.
Published: March 2003

1. Previous studies have shown that among British species, seeds that persist in the soil tend to be small and compact compared with non‐persistent seeds. We tested whether or not this pattern is repeated among 101 Australian species, from a range of habitats.

2. Seed mass was plotted against variance of seed dimensions, across all species. Species with persistent seeds were found across the whole range of seed mass (0·217–648·9 mg) and variance (0·0000–0·2497), providing no evidence for a critical mass or variance which separated persistent from transient seeds.

3. We tested whether or not divergence within individual clades between persistent and transient seeds was associated with increased seed mass or seed dimension variance, using phylogenetically independent contrasts (PICs). There was no consistent tendency found.

4. Thus for Australian species, persistent seeds were not smaller or more compact than transient seeds when compared across all species or when compared using PICs. Presumably the natural history of burial and disturbance operates differently in British and Australian habitats.
Climate change andCognettia sphagnetorum: effects on carbon dynamics in organic soils
Authors: Briones M. J. I. , Ineson P. , Poskitt J.
Published: March 2003

1.A microcosm experiment was performed to test the impacts ofCognettia sphagnetorumon carbon leaching in a cambic stagnohumic gley soil.

2.Leaching of dissolved organic carbon (DOC) was significantly enhanced byC.sphagnetorum,with the greatest effect being found in the upper, 0–6 cm, soil layers. The ratio of DOC to dissolved organic nitrogen (DON) in the leachate decreased in faunated systems, indicating that the enchytraeids were mobilizing carbon from organic matter with a low C to N ratio.

3.The vertical distribution of the enchytraeids had an effect on the production of DOC, and this vertical distribution is affected strongly by climate. It is proposed that increases in DOC found in a field soil‐warming experiment with the same soil are largely a result of changes in the vertical distribution of these organisms.
Which components of diet quality affect retention time of digesta in seabirds?
Authors: Hilton G. M. , Houston D. C. , Furness R. W.
Published: March 2003

1. The nature of the diet can affect the gut retention time of food consumed by an animal, and a theoretical framework has been developed to explain this in terms of optimal digestion rates. However, diets may differ in a number of different attributes, all of which may separately affect the optimal length of time that they are retained in the gut.

2. Here an attempt is made to elucidate which of these features are important in determining gut retention time of different fish species when fed to nine north Atlantic seabird species, and discuss the different potential optimization criteria for retention time in seabirds.

3. Retention times of Lesser Sandeel (Ammodytes marinus Raitt.) were shortest, and this species was also rapidly broken down in vitro. Sprat (Sprattus sprattus (L.)) took longer to be broken down in vitro than Whiting (Merlangius merlangus (L.)), and also had a high energy and lipid content, which might be expected to result in slow digestion; yet retention times of the two species were similar.

4. Meal size also had an important effect on gut retention times, large meals being retained for longer in the gut than small meals, apparently because of an upper limit on the peak excretion rate.

5. Diet and meal‐size related characteristics are important factors influencing prey profitability, prey selection and foraging patterns in seabirds.
Symbiotic N2 fixation in a high Alpine grassland: effects of four growing seasons of elevated CO2
Authors: Arnone Iii J. A.
Published: March 2003

1. Increasing carbon dioxide concentration (E: 680 μl CO2 litre–1vs ambient, A: 355 μl CO2 litre–1) around late‐successional Alpine sedge communities of the Swiss Central Alps (2450 m) for four growing seasons (1992–1995) had no detectable effect on symbiotic N2 fixation in Trifolium alpinum—the sole N2‐fixing plant species in these communities (74 ± 30 mg N m–2 year–1, A and E plots pooled).

2. This result is based on data collected in the fourth growing season showing that elevated CO2 had no effect on Trifolium above‐ground biomass (4·4 ± 1·7 g m–2, A and E plots pooled, n = 24) or N content per unit land area (124 ± 51 mg N m–2, A and E pooled), or on the percentage of N Trifolium derived from the atmosphere through symbiotic N2 fixation (%Ndfa: 61·0 ± 4·1 across A and E plots) estimated using the 15N dilution method.

3. Thus, it appears that N inputs to this ecosystem via symbiotic N2 fixation will not be dramatically affected in the foreseeable future even as atmospheric CO2 continues to rise.