bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial distribution and population dynamics of a benthic rotifer, Embata laticeps (Murray) (Rotifera, Bdelloidea) in the bed sediments of a gravel brook
Authors: SCHMID‐ARAYA J.M.
Published: May 2006

The spatial and temporal distributions of the most abundant bdelloid rotifer, Embata laticeps (Murray), inhabiting the sediment surface and the hyporheic interstitial of a gravel stream were investigated between October 1991 and October 1992. Three temporal peaks of population density occurred during the year at the sediment surface differing in their riming from the density peaks detected within the bed sediments.

 The depth distributions of E. laticeps in pool and riffle areas differed significantly. Higher abundances were found between 10 and 20 cm depth in the pool and between 20 and 30 cm in the riffle area. In these two sites a significant effect of surface discharge (estimated 1 week before sampling) on rotifer densities was found. Discharge greater than 0.424 m3s−1 significantly reduced the densities in the riffle, while only at values greater than 1.660m3s−1 were abundances influenced in the pool area.

 The percentages of egg‐bearing females were higher within the bed sediment than in the surface layer, and in the pool area than in the riffle. Thus, overall mean values of population increase were higher in the pool habitat (x̄= 0.015 ± SE 0.029 day−1) than in the riffle and at the sediment surface (x̄= 0.004 ± 0.025 and 0.005 ± 0.026 day−1, respectively). In addition, population growth fluctuated more strongly at the sediment surface than within the hyporheic intersiritial. Comparison of the observed values of population increase with a randomization test, where observed densities were randomly permuted, revealed no significant differences between those observed and values from a random model. Thus, a clear trend in population growth of E. laticeps over time could not be demonstrated in this gravel stream.
Dispersal of adult Trichoptera at a Danish forest brook
Authors: SODE ANNETTE , WIBERG‐LARSEN PETER
Published: May 2006

The dispersal of adult Trichoptera at the small Danish forest brook, Stamperenden, was studied from 10 May to 6 October 1990 using Malaise traps placed across the brook, parallel to the brook at distances of 2, 20 and 40m, and perpendicular to it at a distance of 1–3m.

 Of the total of 4175 specimens caught, lotic species breeding in Stamperenden accounted for 95.6%. The dominant species were Agapetus fuscipes, Lype reducta, Plectrocnemia conspersa, Potamophylax nigricornis and Silo pallipes.

 The sex ratios in the catches of most species were uneven. Agapetus fuscipes males were in excess, probably because males fly more frequently than females.

 The dominant species flew predominantly above the surface of the brook. Whereas both sexes of A. fuscipes, L. reducta and S. pallipes were rarely found even as little as 20–40m from the brook, the dispersal range of P. conspersa was much wider.

 The implications of low dispersal for the biological recovery of damaged but subsequently restored streams and stream catchments are discussed. It is concluded that complete biological recovery may be a process requiring decades unless the original aquatic fauna is re‐established artificially.
The rise and fall of Asterionella formosa in the South Basin of Windermere: analysis of a 45‐year series of data
Authors: MABERLY S.C. , HURLEY M.A. , BUTTERWICK C. , CORRY J.E. , HEANEY S.I. , IRISH A.E. , JAWORSKI G.H.M. , LUND J.W.G. , REYNOLDS C.S. , ROSCOE J.V.
Published: May 2006

The changes in abundance of Asterionella formosa in the South Basin of Windermere between 1946 and 1990 are described and analysed. The average seasonal cycle for the 45‐year period shows an overwintering population of about 10 cell ml−1 which increases with an exponential rate of 0.09 loge day−1 to an annual maximum of 4000 cell ml−1 by about Day 124. There is then a rapid decline at an exponential rate of loss of 0.29 loge day−1 to values which typically are less than 0.01 cell ml−1 in mid‐summer. By about Day 240 a second period of rapid increase occurs with an exponential rate of increase of 0.18 loge. day−1 to a plateau of about 7 cell ml−1 in late autumn and early winter.

 This average pattern is subject to considerable year‐to‐year variation. The timing and extent of the increase in the autumn was particularly variable. The rate of increase in the spring was strongly positively correlated, and that in the autumn strongly negatively correlated, with the day at which the exponential phase started. Rates for these two phases of increase were not statistically different when expressed in terms of time from mid‐summer, which reinforces earlier conclusions that light availability is the main factor governing the rate of spring increase and suggests that this is also the case for the autumn increase.

 Eight descriptors of seasonal development showed statistically significant changes over the 45 years. Early winter populations declined from 27 to 4 cell ml−1, and linked to this the day at which cell concentrations exceeded 50 cell ml−1 occurred later by 24 days from Day 54 in 1946 to 78 in 1990. The lower early winter population appears to be linked to a lower end of year population as this decreased between 1946 and 1968 from 46 to 2 cell ml−1, and then increased slightly to 7 cell ml−1 in 1990. The start of the spring exponential increase occurred on Day 57 in 1946 and started earlier by 19 days in 1968 but then occurred later, at Day 76, in 1990. The duration of the spring increase got shorter by 23 days, from 67 days in 1946 to 44 days in 1990. The maximum rate of increase rose from 0.065 loge day−1 in 1946 to 0.112 loge day−1 in 1990. The annual maximum declined from 9863 cell ml−1 in 1946 to 2278 cell ml−1 in 1968 and then increased to 6159 cell ml−1 in 1990. The annual geometric mean decreased from 61 cell ml−1 in 1946 to 5 cell ml−1 in 1968 and remained nearly constant subsequently.

 In many cases, the precise underlying causes of these changes were not apparent. However, the increase with time of rate of increase in the spring appeared to be linked to a later start and hence growth under higher light. There was no significant cyclical change in any of the descriptors studied.
Size dependence of composition, photosynthesis and growth in the colony‐forming freshwater ciliate, Ophrydium versatile
Authors: SAND‐JENSEN KAJ , GEERTZ‐HANSEN OLE , PEDERSEN OLE , NIELSEN HELLE SKOVGAARD
Published: May 2006

1. Ophrydium versatile is a symbiotic ciliate which forms gelatinous colonies up to several centimetres in diameter in transparent temperate lakes. The ciliates are evenly spaced at the colony surface and constitute a small proportion of the surface area (7%) and volume (3.1%) of the colony, but a large proportion of organic carbon (74%) and nitrogen content (82%) (exemplified for 1 cm3 colonies). The majority of the colony volume is formed by the jelly. The biomass proportion of ciliates scales inversely with colony size, following the decline of surface area to colony volume. The largest colonies found in Danish lakes in early summer contain almost 1 million ciliates, and assuming they derive from a single ciliate undergoing exponential division, they need twenty generations and, presumably, almost a year to reach maximum size.

2. The ciliates contain numerous symbiotic zoochlorellae that constitute about 10% of ciliate volume and more than half of the carbon content. Zoochlorellae dominate oxygen metabolism of the assemblage, resulting in low light compensation points, a large diel photosynthetic surplus, and a marked dependence on light for sustained growth and ciliate metabolism. Estimated gross photosynthesis (7ng C ciliate−1 day−1) of Ophnrydium from shallow, clear waters in June greatly exceeded the estimated carbon contained in filtered bacteria and small algae (1.9ng C cilicate−1 day−1). Nitrogen and phosphorus content of the prey, however, may provide the main nutrient source consistent with the correspondence between mass‐specific rates of nutrient uptake and measured relative growth rates (average 0.067 day−1, generation time 10 days).

3. The large Ophrydium colonies require increased allocation of photosynthetic carbohydrates with increasing colony size to maintain the jelly. The large colonies tend to become gas‐filled, floating, mechanically destroyed and their ciliate inhabitants abandon them as swarmers. Colony formation, however, should offer protection against predators which may be more important for the natural abundance than the costs of growing in a colony.
Disturbance and the temporal variability of invertebrate assemblages in two Andean streams
Authors: FLECKER ALEXANDER S. , FEIFAREK BRIAN
Published: May 2006

1. Monthly variation in patterns of invertebrate density was examined in two streams in the Venezuelan Andes that differed in elevation, geomorphology, and disturbance regime.

2. At one stream, located in the Andean piedmont, invertebrate densities displayed large fluctuations and between‐month variation differed by as many as four orders of magnitude. Major declines in invertebrate numbers were generally associated with frequent disasters, defined as channel‐shifting spates and drought.

3. At the other stream, a montane site located at higher elevation, invertebrate densities varied by tittle more than an order of magnitude over the duration of the study. Reductions in invertebrate numbers between successive months generally occurred during the rainy season.

4. Monthly invertebrate densities were inversely related to rainfall at each site. In addition, a highly significant positive relationship was observed between invertebrate density and the number of days elapsed since the previous major rainstorm event. Relationships between rainfall and invertebrate densities differed between streams, however, with significantly steeper regression slopes being found at the piedmont than the montane site.

5. We suggest that disturbance plays a seasonally important role in structuring neotropical stream communities in which changes in discharge are severe and unpredictable. Our data contrast with studies from tropical floodplain rivers in which rainy‐season floods are predictable events that cannot be readily characterized as disturbances.
Estimating the abundance of subterranean propagules of submersed aquatic plants
Authors: SPENCER DAVID F. , KSANDER GREGORY G. , WHITEHAND LINDA C.
Published: May 2006

1. Data on sample means (x|) and variances (s2) of propagule abundance for five typos of aquatic plants growing in a variety of habitats were collected. The data set consisted of 379 values for x| and s2, based on 4942 individual sample units (sediment samples), drawn from the literature or from data collected as part of this study.

2. Regression analysis relating log s2to log x| yielded an equation which was solved for the number of sample units (n) required to achieve a given degree of precision. For precise estimates [standard error (SE) = 20% of x|], values ofnbetween twenty‐seven and 234 are required when propagule density is low (<200m−2), whereas eight to twenty‐six sample units are required when propaguie density is high (200–1000 m−2). For larger SE (i.e. 30% of x|),ndecreased by about 50%. Sampler area (20 to 1600cm2) did not affect estimates ofn.

3. Time required to collect and process sediment cores (collected with either a 5, 10, or 15cm corer) was approximately 7, 10, or 13min, respectively. Combining this information with the required number of samples is useful in planning studies designed to measure changes in the abundance of underground propagules of submersed aquatic plants.
Longitudinal effects of herbivory on lotic periphyton assemblages
Authors: McCORMICK PAUL V. , LOUIE DENISE , CAIRNS JOHN
Published: May 2006

1. The longitudinal effects of herbivory on stream periphyton assemblages were examined in laboratory stream channels, each of which consisted of an upstream chamber, which either contained snail grazers or not, and downstream chambers, none of which contained grazers. Periphyton assemblages of two ages (0–21 days old and 21–42 days old) were sampled in both upstream and downstream chambers to detect proximate (i.e. localized) and longitudinal (i.e. downstream) effects of herbivory.

2. Both proximate and longitudinal effects were detected, although they differed in their impact on the periphyton assemblage. Periphyton biomass and cell accumulation were lower in grazed than in ungrazed upstream chambers throughout the experimental period. Accumulation rates on initially bare tiles were substantially higher downstream of grazed than of ungrazed chambers, but grazing had no effect on cell densities in established (21–42 day old) assemblages downstream.

3. Longitudinal effects of herbivory were not due to quantitative differences in the flux of propagules or nutrients from grazed and ungrazed chambers. Although not tested in this study, it is hypothesized that differences in the physiological condition of exported propagules may have contributed to differences in downstream colonization rates in grazed and ungrazed streams.

4. The magnitude of longitudinal impacts of herbivory and the importance of different causal mechanisms are predicted to vary depending on the standing crop and productive capacity of the periphyton assemblages as well as the consumptive demand of the herbivore guild.
Recurrent response patterns of a zooplankton community to whole‐lake fish manipulation
Authors: HE XI , SCHEURELL MARK D. , SORANNO PATRICIA A. , WRIGHT RUSSELL A.
Published: May 2006

1. In a series of whole‐lake manipulations conducted from 1984 to 1991, planktivorous fishes were alternately removed and restocked in a small mesotrophic lake, resulting in dramatic changes in the zooplankton community.

2. Response patterns in the zooplankton community, which include species and size structure, and within‐year community variability, were examined. Variation in the zooplankton community in unmanipulated years was much lower than that in manipulated years, regardless of direction of the manipulation (i.e. decreasing or increasing planktivory).

3. The succession of zooplankton species abundance was repeated in the second removal of planktivorous fishes. The community shifted from small‐bodied cladocerans, copepods and rotifers, through an intermediate state with high abundance of Holopedium, to an assemblage dominated by large‐bodied daphnids.
The role of drought in the impact of climatic change on the microbiota of peatland streams
Authors: FREEMAN C. , GRESSWELL R. , GUASCH H. , HUDSON J. , LOCK M.A. , REYNOLDS B. , SABATER F. , SABATER S.
Published: May 2006

1. Simulation of climate change (summer drought) stimulated autotrophy in a stream draining a Welsh peatland. Biofilm autotrophic biomass (chlorophyll) increased by 145% and was correlated with an increased overall metabolic activity (r = 0.75, P<0.05). Bacterial population densities were not significantly affected.

2. The increased autotrophy was probably related to a decrease in the organic:inorganic ratio of nutrients released from the wetland to the stream.

3. Bacterial reserves of poly‐β‐hydroxyalkanoate (PHA) fell by 51%. Increased nitrate concentrations were inversely correlated with autotrophic diversity (r=−0.88, P < 0.001).

4. The increased autotrophic biomass represents an increased nutrient supply for the higher trophic levels which could promote higher productivity within the stream ecosystem as a whole.

5. The simulation also caused a cooler (11%, P<0.01) streamflow from the drought‐impacted wetland, which could mitigate against any adverse temperature‐dependent effects of future climatic change.
Glacial rivers: physical habitat and ecology
Authors: MILNER ALEXANDER M. , PETTS GEOFFREY E.
Published: May 2006

1. This review examines the physical habitat and ecology of glacial rivers which have been relatively unstudied compared with rivers originating from other sources.

2. Typical glacial rivers have summer temperatures below 10°C, a single seasonal peak in discharge, which in the Northern Hemisphere typically occurs in July, a diel fluctuation in flow which usually peaks in late afternoon, and turbidity levels in summer that exceed 30 NTU. These variables contrast with those in snowmelt/rainfall streams, particularly in summer, and make conditions more extreme for the biota.

3. Where maximum temperatures are 2°C benthic invertebrate communities are dominated by Diamcsa (Chironomidae). Downstream, temperatures increase, channels become more stable and valley floors become older. Orthocladiinae (Chironomidae), Simuliidae, Baetidae, Nemouridae and Chloroperlidae become characteristic members of the invertebrate community.

4. Fauna may be displaced, or at least colonization delayed, by channel instability; the variable age structure of the valley floor will influence the faunal gradient, which may also be reset by the effects of tributaries, lakes and valley confinement.

5. We propose a qualitative model that outlines zoobenthic community gradients determined by two principal variables, water temperature and channel stability, as a function of distance downstream, or time since deglaciation.
Macroinvertebrate communities of streams in western Nepal: effects of altitude and land use
Authors: SUREN ALASTAIR M.
Published: May 2006

1. The influence of altitude and land‐use changes on macroinvertebrate assemblages from riffles in forty‐three streams in the Dolpo region of western Nepal were examined. Sampling sites ranged in altitude from 850 to 4250m, and land‐use patterns fell into five categories: alpine, forest, grassland, pasture and agricultural land.

2. TWTNSPAN classification of physicochemical data separated streams into groups on the basis of climatic and physical factors. Streams from high, cold, alpine areas were separated from those in warmer, lower, agricultural areas.

3. In all, 138 macroinvertebrate taxa were collected from fifty‐three insect families. Ephemeroptera were most common, especially Baetidae.

4. Taxonomic richness declined with increasing altitude. Ten insect families were significantly more abundant in lowland streams, and five were more common in alpine streams.

5. TWINSPAN and DECORANA revealed distinct invertebrate groupings of the forty‐three streams surveyed. A high percentage of the variance (79.3%) in ordination space was explained by DECORANA axes 1 and 2. Altitude, temperature, stream width and land use were implicated in structuring invertebrate communities.
Macroinvertebrate community structure and altitudinal changes in the upper reaches of a warm temperate southern African river
Authors: PALMER CAROLYN , PALMER ANTHONY , O'KEEFFE JAY , PALMER ROBERT
Published: May 2006

1. The Buffalo River rises 1200m above sea level, drops 600m in the first 7km, and a further 100m in the next 30 river kilometres. Macroinvertebrates were sampled, and environmental variables measured monthly in 1987, at four sites along this part of the river.

2. Flow at the headwater site (1120m a.s.l., 1 km from the source) was seasonal, though pools remained and subterranean flow was continuous. Twelve macroinvertebrate taxa were found exclusively at this site, where conductivity, pH and nutrient concentrations were low.

3. Flow at the foothill site (530m a.s.l., 7km from the source) was perennial. The invertebrate community, although distinct from that at downstream sites, lacked the unique taxa of the headwater site. Conductivity, pH and nutrient concentrations were higher.

4. The two sites downstream of the foothills (450m a.s.l., 18km from the source, and 410m a.s.l., 31 km from the source), had similar invertebrate communities. Conductivity, pH and nutrient concentrations were higher than at the upper sites.

5. Community structure changed most between the headwater and foothill sites. This paralleled changes in river steepness rather than changes in measured physicochemical variables.
Theoretical habitat templets, species traits, and species richness: aquatic Coleoptera in the Upper Rhône River and its floodplain
Authors: RICHOUX PHILIPPE
Published: May 2006

To test predictions of the river habitat templet and the patch dynamics concept, trends in species traits and species richness of aquatic beetles were related to the spatial‐temporal variability of eighteen habitat types in the alluvial floodplain of the French Upper Rhône River. One hundred and twenty species of beetles were used in this analysis.

The basic information was obtained either from the literature (for most of the species traits) or from observations made at approximately 500 sampling sites in the Brégnier‐Cordon and Jons sections over the past 19 years (for habitat utilization). This information was structured by a fuzzy coding technique and examined by ordination analyses.

Analyses of the relationships among nineteen species traits revealed a clear distinction according to traits such as body form (for adults), functional feeding type and food (adults and larvae), attachment to the substrate and dissemination potential (adults and larvae), and patterns of aquatic and/or terrestrial life of adults and larvae. Species traits such as number of descendants per reproductive cycle, and number of reproductive cycles per year or per individual showed less contrast, because these traits are rather homogeneous in aquatic beetles.

Analyses of the habitat utilization by the aquatic beetles revealed a vertical gradient that separates interstitial from superficial habitats, and a transverse gradient for the superficial habitats, which extends from the main channel towards permanent oxbow lakes and temporary waters.

The significant relationship betweeen species traits and habitat utilization demonstrates that most beetle species use a particular set of habitat types with a particular set of species trait modalities.

Species traits of aquatic beetles are homogeneous but evidently very successful and are adapted to many potential conditions of spatial–temporal variability. Because of this homogeneity, observations on aquatic beetles do not support trends of traits in the framework of spatial–temporal variability predicted from the river habitat templet.

The observed species richness of aquatic beetles is low in habitat types with a low spatial–temporal variability, increases as spatial variability increases, and tends to be highest at intermediate temporal variability. This pattern matches predictions of the patch dynamics concept.
Theoretical habitat templets, species traits, and species richness: Trichoptera in the Upper Rhône River and its floodplain
Authors: TACHET HENRI , USSEGLIO‐POLATERA PHILIPPE , ROUX CHANTAL
Published: May 2006

For Trichoptera occurring in two sites of the Upper Rhône River (France) we examine: (i) relationships among species traits; (ii) habitat utilization of Trichoptera species; (iii) the relationship between species traits and habitat utilization; (iv) trends of species traits in the framework of spatial–temporal habitat variability to test predictions of the habitat templet concept; and (v) trends of species richness in the framework of spatial–temporal habitat variability to test predictions of the patch dynamics concept.

Of the sixteen species traits selected, twelve have high correlation ratios for the seventy‐five species used in this analysis; these traits are related to behavioural, morphological, or physiological aspects. Traits related to reproduction or life cycle have lower correlation ratios.

An ordination by species traits separates the five main families into three groups: (i) Hydropsychidae and Polycentropodidae; (ii) Hydroptilidae; and (iii) Leptoceridae and Limnephilidae. An ordination of the habitat utilization of the species in ten habitats indicates that the Hydropsychidae occur preferentially in the main channel, Hydroptilidae, Polycentropodidae, and Limnephilidae occur in backwaters or oxbow lakes, and the Leptoceridae are ubiquitous.

The Hydropsychidae exhibit a relationship between species traits and habitat utilization, i.e. they use similar habitat types with similar species traits. The species traits of the other four families are similar but their habitat utilization is quite different.

The Hydropsychidae occur in lowest spatial–temporal variability habitats and Limnephilidae in the highest. Therefore, net spinners and filterers are characteristic of habitats with a low spatial–temporal variability, whereas shredders and case makers using plant material are characteristic of habitats with high spatial–temporal variability. The trends in species traits show little agreement with trends predicted from the river habitat templet.

Trends of species richness in the framework of spatial and temporal variability do not follow the predictions of the patch dynamics concept because richness is similar in all superficial habitats. This implies that each habitat, in spite of large differences in their spatial and temporal variability, offers Trichoptera a similar but limited number of ecological niches.
Sulphate reduction in the hypolimnion and sediments of Lake Kinneret, Israel
Authors: HADAS O. , PINKAS R.
Published: May 2006

1. Lake Kinneret is a warm (13–30°C) monomictic lake. Between January and June a heavy annual bloom of the dinoflagellate Peridinium gatunense dominates phytoplankton biomass (250 g m−2). At the beginning of the summer, degradation and decomposition of the Peridinium biomass occurs, serving as a trigger for intense sulphate reduction in the hypolimnion and sediments.

2. The rates of sulphate reduction in the sediments varied seasonally from 12 to 1700 nmol SO4.−2 reduced cm−3 day−1 in December and July, respectively. The availability of organic matter and sulphate is high in June after the crash of the Peridinium bloom and the beginning of stratification and is lowest in December before overturn.

3. Sulphate concentrations in the hypolimnion range between 0.52 mM and 0.20 mM during mixing (January‐April) and before overturn (December), respectively. The depletion in sulphate in the hypolimnion is stoichiometrically correlated to the increase in sulphide. The lake is not depleted of sulphate at any time, so the sulphate reduction process in Lake Kinneret is not limited by sulphate concentrations except in the sediments just before overturn.
Deep‐water aquatic plant communities in an oligotrophic lake: physiological responses to variable light
Authors: HOWARD‐WILLIAMS CLIVE , SCHWARZ ANNE‐MAREE , VINCENT WARWICK F.
Published: May 2006

1. Oligotrophic Lake Waikaremoana, New Zealand, is used for hydroelectric power generation and the lake levels are manipulated within an operating range of 3 m. There was concern that rapidly changing water levels adversely affected the littoral zone by decreasing light availability in two ways: local turbidity caused by shoreline erosion at low water levels; and decreased light penetration to the deep littoral zone caused by high water levels in summer.

2. The littoral zone was dominated by native aquatic plants with vascular species to 6 m and a characean meadow below this to 16 m. The biomass and heights of the communities in the depth zone 0–6 m were reduced at a site exposed to wave action relative to those at a sheltered site. However, the community structure below 6 m was similar at exposed and sheltered sites. The lower boundary of the littoral zone was sharply delimited at 16 m and this bottom boundary remained constant throughout the year despite large seasonal changes in solar radiation and the 3 m variation in lake level.

3. There was evidence that the deep‐water community consisting of Chara corallina had adapted physiologically to low‐light conditions. Net light saturated photosynthesis (CO2 exchange) per unit chlorophyll a (Chl a) was reduced to 1.7 μg C (μg Chl a)−1 h−1 at the lower boundary, half of that recorded at 5 m. The concentration of Chi a per gram of biomass (dry weight), was considerably greater at the lower boundary than higher in the profile [c. 7 mg Chl a (g dry wt)−1 at 16 m vs. 4 mg Chl a (g dry wt)−1 at 5 m]. Chl b also increased with depth and there was no change in the ratio of Chl a and Chl b with increasing depth. The saturation light intensity (Ik) of the community at the lower boundary was only 78 μmol photons m−2 s−1. Photosynthetic parameters (Ik and α) as well as the Chl a content remained relatively constant throughout the seasonal and short‐term changes in radiation.

4. The photosynthetic characteristics of the littoral community were therefore not greatly affected by the lake level change caused by the present hydroelectric operations. However, the sharpness of the lower boundary and its extreme shade characteristics imply that the deep‐water community would be sensitive to any further changes in underwater light availability.
Nutrient enrichment effects on biofilm metabolism in a Mediterranean stream
Authors: GUASCH HELENA , MARTÍ EUGÈNIA , SABATER SERGI
Published: May 2006

1. Biofilm biomass and metabolism were analysed in La Solana, a calcareous, undisturbed second‐order stream. Measurements were carried out in two Mediterranean climatic extremes, summer and winter. Two on‐site experimental channels were used to study changes following nutrient addition to one of them.

2. Algal biomass (chlorophyll a), NDPP (net daily primary production), GDPP (gross daily primary production) and R (respiration) increased in the enriched channel, and these increases were greater in summer.

3. Photosynthetic capacity (Pmaxchl) decreased during summer, possibly due to enhanced self‐shading accompanying the increase in biomass.

4. In winter, Pmaxchl increased and reached values similar to those in the summer control channel. Because grazing was low, the higher values of Pmaxchl were attributed to partial substitution of the cyanobacterial assemblage by a green‐algae dominated assemblage with higher photosynthetic capacity as well as the low increase in biomass preventing any significant self‐shading.
The impact of pH on interactions among phytoplankton algae, zooplankton and perch (Perca fluviatilis) in a shallow, fertile lake
Authors: BEKLIOGLU MERYEM , MOSS BRIAN
Published: May 2006

1. The combined effects of increasing pH (< 9–11) and increasing densities of perch (0, two, four per enclosure) have been investigated in polyethylene enclosures of volume about 1100 1 in a shallow, fertile lake in Cheshire.

2. Increasing pH decreased carbon dioxide concentrations, chlorophyll a concentrations and diatom biomass. It led to increases in the proportions of Cryptophyta (to pH 10) and Chlorophyta (to pH 11). Although ample inocula were present, significant growths of cyanophytes were not recorded, contrary to expectation.

3. Increasing pH led to increases in numbers of Daphnia hyalina particularly at pH 10 but collapse at pH 11. This persistence at pH 10, independent of perch number, is attributed to reduced feeding of the fish, which survived at this pH. Other zooplankters (Ceriodaphnia spp., Bosmina longirostris, Polyphemus pediculus, Cyclops spp.) all declined with increasing pH.

4. Increasing fish density resulted in an increase in chlorophyll a concentration and in the biomass of Chlorophyta but had no effect on cyanophyte or cryptophyte biomass.

5. Increasing fish density led to declines in Daphnia in the untreated lake‐water controls (pH < 9) and at pH 9, but had no effect at pH 10 where Daphnia hyalina was very abundant. Numbers of Ceriodaphnia spp. and Bosmina longirostris increased with increasing fish density, whilst numbers of Polyphemus pediculus and Cyclops spp. were independent of it.

6. The results are discussed in the light of contemporary knowledge of the factors resulting in large cyanophyte growths and of the factors controlling the stability of macrophyte‐dominated and phytoplankton‐dominated states in shallow lakes. The interaction between pH and fish density and consequent non‐linear response of Daphnia hyalina is particularly notable because of the significance of zooplankton grazing in shallow lakes.
The application of habitat templets and traits to hyphomycete fungi in a mid‐European river system
Authors: PATTEE E. , CHERGUI H.
Published: May 2006

1. The general knowledge about hyphomycetes is summarized and traits of some of these organisms in the Rhône floodplain are described to assess compliance with the river habitat templet (RHT) and patch dynamics concept (PDC) hypotheses. This investigation corresponds with those for other taxonomic groups reported in a recent Freshwater Biology Special Issue on the Ecology of the Upper Rhône River (Statzner, Resh & Dolédec, 1994).

2. Three groups of fungi were considered: aquatic, terrestrial, and aero‐aquatic hyphomycetes.

3. The main factors controlling distribution of these micro‐organisms are food (mostly organic matter), dissolved oxygen and biotic interactions.

4. With contrasting strategies, hyphomycetes exploit both fallen leaves, a discrete ephemeral resource, and wood fragments, which are more durable.

5. Fungal propagules (spores, hyphae) are distributed in the water, and even the air, largely throughout the year. This explains the resilience of these organisms to disturbance.

6. A major problem is the spatial (boundary layer, dead zones) and temporal (leaf input) scale at which these micro‐organisms live and their interactions at the scale adopted for the other organisms referred to in the Special Issue on the Ecology of the Upper Rhône.

7. Our scant knowledge of the microbial ecology in the Rhône floodplain, together with the scale problem and high microbial resilience to environmental stress, render the RHT and PDC hypotheses difficult to test. Only three traits could be tested on hyphomycetes, but all three confirmed the RHT hypotheses.

8. Hyphomycete communities appear to be biologically controlled in more favourable and temporally stable environments, and physico‐chemically controlled in harsher and more perturbed environments.
Microfaunal response to fertilization of an arctic tundra stream
Authors: RUBLEE P. A. , PARTUSCH‐TALLEY A.
Published: May 2006

1. As part of a whole‐system study, the response of the heterotrophic microfaunal community colonizing artificial substrata (polyfoam units) to fertilization of an arctic tundra stream was followed for 6 weeks during the summer.

2. Dominant heterotrophic microfauna observed included amoebae (approximately 40% of colonizing biomass), rotifers (36% of biomass) and ciliates (25% of biomass).

3. Biomass of heterotrophic microfauna on artificial substrata was not significantly different in a control reach and an experimental reach fertilized with phosphorus (loading rate ten times ambient), but in a reach fertilized with both phosphorus and nitrogen (loading rates ten times ambient) biomass was double that of the control and phosphorus‐fertilized reaches. The lack of response in the phosphorus reach was probably due to greater insect grazing as a result of previous phosphorus fertilization of this reach.

4. Abundance of microfauna on epilithic surfaces in the river was higher on rocks from pools than on rocks from riffle areas, but abundance on the artificial substrata was higher than on the natural rocks.

5. The results suggest that microfauna of arctic tundra streams are regulated by grazers and that their importance in transfers among trophic levels is greater in pools than in riffles.
Fossil record of cladoceran and algal responses to fishery management practices
Authors: MISKIMMIN BRENDA M. , LEAVITT PETER R. , SCHINDLER DAVID W.
Published: May 2006

1. We hypothesized that the fishery management practices of toxaphene application and trout stocking would affect non‐target organisms in lakes. Because these practices were rarely monitored in the past, cladoceran and algal assemblages were quantified in sediment cores from two lakes treated 30+ years ago to determine the long‐term response of organisms near the base of the food chain.

2. Chydorids were remarkably resistant over the short term (a few years) in both the oligotrophic and eutrophic lakes despite toxaphene treatments that extirpated native fish and other invertebrates. In the oligotrophic lake (Annette Lake), six chydorid taxa were less abundant in the years following treatment, although no loss of species richness was detected. In the eutrophic lake (Chatwin Lake), the dominant Chydorus cf. sphaericus declined coincident with toxaphene treatment, but longer‐term declines of all taxa were probably related to food web or other changes rather than to toxaphene toxicity. Cause and effect coupling was complicated by the fact that many chydorids were present at low concentrations in some pretreatment samples.

3. The algal communities (as fossil pigments) responded to treatment differently in the two lakes. In the oligotrophic lake, planktonic diatoms, dinoflagellates and chlorophytes were replaced as dominants by deep‐water or benthic blooming cryptophytes, chrysophytes and cyanobacteria. This shift occurred along with increases in large daphnids and the ‘grazing indicator’, pheophorbide a. While both lakes appear to have had enhanced pigment preservation following treatment, the eutrophic lake encountered few long‐term changes in its fossil pigment assemblage. Redundancy analysis estimated that the presence or absence of stocked trout explained much of the variation in the algal assemblages, particularly in the oligotrophic lake.

4. Toxaphene remained elevated in profundal sediments from these lakes 30 and 35 years after treatment.
The effects of iron and manganese on diatom colonization in a Vermont stream
Authors: WELLNITZ T.A. , SHELDON S.P.
Published: May 2006

1. Neutral streams with elevated concentrations of iron and manganese can develop blooms of ferromanganese‐depositing bacteria within oxide deposition zones. Algal abundance declines within these blooms. An in situ experiment was conducted in a Vermont stream to assess the importance of increased concentrations of iron and manganese, without the confounding effects of ferromanganese‐depositing bacteria, on limiting diatom colonization.

2. Diatom abundance in treatments receiving iron increased over time, but densities were lower by a factor of ten or more compared with either control or manganese treatments. These results indicate that the presence of ferromanganese‐depositing bacteria is not necessary for lowering algal abundance.

3. We speculate that ferromanganese‐depositing bacteria may thrive in iron oxide deposition zones, in part because iron oxides help displace periphytic algae which may be superior competitors for space and/or limiting nutrients.
The horizontal distribution of plankton in a deep, oligotrophic lake—Loch Ness, Scotland
Authors: JONES R.I. , FULCHER A.S. , JAYAKODY J.K.U. , LAYBOURN‐PARRY J. , SHINE A.J. , WALTON M.C. , YOUNG J.M.
Published: May 2006

1. The horizontal distribution of plankton in Loch Ness, a deep, oligotrophic lake with a simple trench morphometry, was studied on three occasions in 1993. Samples were collected from ten stations spaced along the length of the loch and the abundance of algae, bacteria, protozoa, rotifers and crustacean zooplankton was determined.

2. Horizontal variability was found to be greatest for the metazoan zooplankton and for the algae, especially two cryptomonad flagellates. Bacteria and heterotrophic protozoa showed relatively little horizontal variability. The degree of horizontal variability was not sufficient seriously to affect studies of the seasonality of plankton abundance conducted from a single sampling station.

3. Gradients of plankton distribution along the length of the loch were dependent on the recent wind history. The direction of the gradient could readily reverse with a shift in wind direction. These results indicate that the horizontal distribution of plankton in Loch Ness is more dependent on wind‐induced water circulation patterns than on differential growth of plankton in water masses of differing chemistry.
Use of an encounter model to predict size‐selective predation by a stream‐dwelling cyprinid
Authors: RINCÓN PEDRO A. , LOBÓN‐CERVIÁ JAVIER
Published: May 2006

1. The increased probability of detection of larger prey in the drift appeared to be the major determinant of prey consumption by red roach (Rutilus arcasi) in an Iberian stream. We developed a model of prey encounter incorporating this factor that explained 68% of the overall variation in the consumption of prey of different size. When the same model was applied to benthic size distributions the variance explained was 16%.

2. Gape‐limited ingestion also was a significant factor influencing prey consumption and, when added to the model, the variance explained increased to 85% (32% for the benthos), but its importance was strongly dependent on both: (i) the maximum prey size available and (ii) fish size.

3. The exact shape of red roach reactive fields and, as a consequence, their degree of size‐selectivity appeared to vary seasonally and ontogenetically. In summer, younger fish exhibited apparently reduced reactive fields. We hypothesize that this can be the result of factors such as microhabitat shifts or a reduced range of prey sizes.
Estimating morphologically determined connectance and structure for food webs of freshwater invertebrates
Authors: WARREN PHILIP H.
Published: May 2006

1. Connectance is a parameter of central importance in determining food‐web structure, but the processes determining its value remain unclear. In evaluating possible explanations it is useful to know what patterns, and values, of connectance occur in food webs assembled at random from a set of species in a regional species pool; i.e. where the number of links is determined by the morphological features of the species present, not by the immediate effects of energetics or stability on the particular web.

2. This study examines, by means of laboratory experiments, the occurrence of potential feeding interactions among a set of freshwater invertebrate species randomly selected from different freshwater sites in a geographical region. The results from pairwise feeding trials are used to construct two ‘theoretical’ food webs, in which the patterns and values of connectance are examined.

3. Analyses of these webs indicate that their structure is consistent with the observed values in previously documented ‘real’ webs. Directed connectance values of 0.12–0.16 (or less) suggest that the assembled webs are no more connected than many freshwater webs from natural systems. The number of links per species increases curvilinearly with the number of species, during web assembly, consistent with recent hypotheses.

4. These results also indicate that quantifying, and understanding the determinants of, trophic generalism or specialism does have implications for understanding how connectance is constrained in real webs. Freshwater invertebrates seem to be relatively generalist, and freshwater food webs perhaps correspondingly highly connected. Such arguments have implications for interpreting other aspects of food‐web structure in these systems, and for parameterizing models that are based on connectance.
APPLIED ISSUES The effect of ammonium nitrate on the feeding and development of larvae of the smooth newt, Triturus vulgaris (L.), and on the behaviour of its food source, Daphnia
Authors: WATT PENELOPE J. , OLDHAM ROBERT S.
Published: May 2006

1. Larvae of the smooth newt, Triturus vulgaris, were exposed to four concentrations of ammonium nitrate in artificial pond water (50, 100, 200 and 500 mg 1‐−1) under controlled laboratory conditions.

2. Larvae exposed to a 50 mg 1‐−1 solution of ammonium nitrate showed no significant difference to control larvae in feeding rate, mass at metamorphosis or time to metamorphosis. However, larvae exposed to 200 or 500 mg 1‐−1 ammonium nitrate, for a single period of 24, 48 or 72 h, were significantly smaller than controls at metamorphosis. Larvae exposed to 100 mg 1‐−1 had a significantly higher feeding rate than those reared under control conditions or those exposed to 200 or 500 mg 1‐−1 ammonium nitrate, but this was not reflected in their size at metamorphosis, which was not significantly different from the controls. Larval survival remained high in all trials.

3. In separate trials, Daphnia, used as a food source for the newt larvae, were exposed to the same series of ammonium nitrate concentrations. Daphnia behaviour was affected by exposure to 200 and 500 mg 1‐−1 ammonium nitrate, and in both cases animals were significantly more likely to be found at the top of the water column than those exposed to 50 or 100 mg 1‐−1 ammonium nitrate or the control medium.
A critical appraisal of prognostic and predictive factors for common lung cancers
Authors: Thunnissen F B J M , Schuurbiers O C J , Den Bakker M A
Published: May 2006

The outlook for patients with lung cancer remains poor despite advances in the understanding of the pathology and biology of this disease. To optimize treatment protocols prognostic data are essential. The current era with molecular research on mRNA expression analysis and proteomics will lead to a plethora of new molecular markers, which are likely to be correlated, at least in part, with each other and with disease activity, progression and survival. However, although the number of prognostic factors analysed in published systematic reviews on lung cancer is large, the scope of these factors in individual studies is often narrow. In daily practice prognostic factors other than general TNM staging are not implemented. To assess the efficacy of new prognostic factors for the management of individual patients with non‐small cell lung cancer, studies with clinically relevant modelling are required. In this review arguments are provided to use a model combining radiological and histopathological growth rate, histopathological diagnosis and molecular characteristics as markers for metastatic capacity, tumour volume doubling time and expected response to targeted therapy. This may reveal time‐related predictive information useful for treatment guidance of the individual patient.
Simultaneous immunohistochemical expression of HBME‐1 and galectin‐3 differentiates papillary carcinomas from hyperfunctioning lesions of the thyroid
Authors: Rossi E D , Raffaelli M , Mule' A , Miraglia A , Lombardi C P , Vecchio F M , Fadda G
Published: May 2006

Aims : The histological diagnosis is critical for the postsurgical management and follow‐up of thyroid malignancies. The differential diagnosis between papillary carcinoma and hyperfunctioning lesions, either with papillary hyperplasia or with a follicular architecture, can create real diagnostic difficulty. The aim of this study was to evaluate the expression of several antibodies considered to be markers of malignancy in malignant and hyperfunctioning thyroid neoplasms and to include the most effective of them in a diagnostic panel.

Methods and results : One hundred resected thyroid nodules—58 hyperfunctioning benign lesions and 42 papillary carcinomas (14 follicular variant, 14 macrofollicular variant and 14 classic type)—were immunohistochemically studied for HBME‐1, galectin‐3, cytokeratin (CK) 19 and RET‐proto‐oncogene. HBME‐1 and galectin‐3 showed 92.8% and 89% sensitivity, respectively, and their coexpression was present in 36 out of 42 papillary carcinomas (85.7%) and absent in non‐malignant lesions. Their association increased sensitivity to 94.7% and the diagnostic accuracy to 97.9% and involved the highest number of cases (95%) in comparison with two other panels including, respectively, three (HBME‐1, galectin‐3, CK19) and all four antibodies.

Conclusion : An immunohistochemical panel consisting of HBME‐1 and galectin‐3 can make a correct distinction between malignant and hyperfunctioning thyroid neoplasms with high diagnostic accuracy.