bluuebunny/crossref_metadata_2025 huggingface dataset:
Macroinvertebrate drift in streams of the Nepalese Himalaya
Authors: BREWIN PHILIP A. , ORMEROD S.J.
Published: May 2006

1. Macroinvertebrate drift was investigated in seven small headwater streams along an altitudinal gradient (600–3350 m) in two adjacent river systems in east‐central Nepal. Study streams in the Likhu Khola were at the lowest altitude and flowed through terraced agriculture. At higher altitudes, Langtang streams flowed through catchments of forest and alpine scrub. Samples were collected every 3h over a 24 h period in each stream.

2. Terrestrial macroinvertebrate drift was greatest in streams with semi‐natural catchments, but was scarce in streams where trees were absent.

3. At lower altitudes drift was dominated by Hydropsychidae and Baetidae, which were most abundant in night samples, and Hydracarina, which tended to be day active. Baetidae also dominated drift at high altitudes, but here drift was increasingly aperiodic or diurnal. The composition of the drift reflected a significant correlation between the percentage abundance of taxa in the drift and benthos.

4. As in other mountain regions of the world, drift was aperiodic in fishless streams (high altitude), but strongly nocturnal in streams where insectivorous fish were present (lower altitude). However, a wide array of potentially important variables along the altitudinal gradient, such as temperature, climate and community structure, might be important influences on these patterns.
International collaboration in freshwater ecology
Authors: RESH VINCENT H. , YAMAMOTO DAVID
Published: May 2006

1. International collaboration in freshwater ecology was examined using authorship affiliations of articles published in thirty‐three specialized journals. Most are published in Europe.

2. Researchers from four to thirty‐seven different countries were represented in the 100 articles examined for each journal. Only 29% of articles were single‐authored; multicountry authors' addresses (indicating international collaboration) were found for 9% (range 0–23% per journal) of articles examined.

3. Five of the eighty‐nine countries listed in the addresses of the 3300 articles together contributed >50% of total articles: United States (24.9%), Canada (8.6%), Germany (7.6%), Commonwealth of Independent States (7.0%) and Poland (5.9%). Of the fifteen countries that each produced >2.5% of total articles, the percentage representing international collaboration was highest for France (34.9%) and Canada (24.0%). The seventy‐four countries that each contributed <2.5% of total articles generally had higher rates of international collaboration.

4. Researchers in the United States and Canada collaborate internationally almost twice as often in freshwater ecology than in all science. Much of France's extensive international collaboration is with countries that produce few articles in freshwater ecology, and their international collaboration is often exclusively with France.

5. Three journals publishing both marine and freshwater ecology articles contain more articles on the former topic, but more countries are represented in the publication of freshwater than marine research.

6. The percentage of articles that represent international collaboration is higher in freshwater ecology than in medicine, biology, chemistry and engineering, and approximates that in physics.
The synthesis of long‐term ecological research in the context of concurrently developed ecological theory: design of a research strategy for the Upper Rhône River and its floodplain
Authors: STATZNER BERNHARD , RESH VINCENT H. , ROUX A. LOUIS
Published: May 2006

Using sites from the Upper Rhône River, France, as an example, the objective of this paper is to identify the essential elements needed to test current ecological theories with previously collected data. Procedures developed may enable other groups to design comparable research strategies for syntheses of long‐term studies of ecological systems.

Because of the high number (more than 200) and turnover of researchers, the long study period (about 17 years), the evolution of research methods and interests, and the diverse systematic groups that were considered (from micro‐organisms to birds), the data available for a synthesis were quite heterogeneous. The application of a ‘fuzzy coding’ technique allowed such disparate information to be structured for analysis.

The habitat templet concept and the patch dynamics concept were selected for analysis with existing data on the Upper Rhône because theories, such as these, that link ecological responses to habitat templets are a focus of current ecological debate and potentially may serve as a general tool for ecologically orientated river management.

A preliminary trial to structure the existing knowledge, to identify (and manage) gaps in it, and to create and apply the analytical tools in a way that predictions from theory could be tested was an essential element in the design of this project.

Predictions derived from the theoretical concepts had to match the format of the available information on the Upper Rhône; potential bias was avoided by having a priori predictions developed by previously uninvolved colleagues.

Synthesis of the long‐term study of the Upper Rhône in the context of concurrently developed ecological theory required, at times, an unconventional research strategy. Hence, the generation of hypotheses and methods, the presentation of results, and consequently the discussions in papers of this special issue of Freshwater Biology (Statzner, Resh & Dolédec, 1994) represent an innovative approach to testing ecological theory.
A fuzzy coding approach for the analysis of long‐term ecological data
Authors: CHEVENE FRANçOIS , DOLÉADEC SYLVAIN , CHESSEL DANIEL
Published: May 2006

We present an unconventional procedure (fuzzy coding) to structure biological and environmental information, which uses positive scores to describe the affinity of a species for different modalities (i.e. categories) of a given variable. Fuzzy coding is essential for the synthesis of long‐term ecological data because it enables analysis of diverse kinds of biological information derived from a variety of sources (e.g. samples, literature).

A fuzzy coded table can be processed by correspondence analysis. An example using aquatic beetles illustrates the properties of such a fuzzy correspondence analysis. Fuzzy coded tables were used in all articles of this issue to examine relationships between spatial‐temporal habitat variability and species traits, which were obtained from a long‐term study of the Upper Rhône River, France.

Fuzzy correspondence analysis can be programmed with the equations given in this paper or can be performed using ADE (Environmental Data Analysis) software that has been adapted to analyse such long‐term ecological data. On Macintosh AppleTM computers, ADE performs simple linear ordination, more recently developed methods (e.g. principal component analysis with respect to instrumental variables, canonical correspondence analysis, co‐inertia analysis, local and spatial analyses), and provides a graphical display of results of these and other types of analysis (e.g. biplot, mapping, modelling curves).

ADE consists of a program library that exploits the potential of the HyperCardTM interface. ADE in an open system, which offers the user a variety of facilities to create a specific sequence of programs. The mathematical background of ADE is supported by the algebraic model known as ‘duality diagram’.
Theoretical habitat templets, species traits, and species richness: aquatic oligochaetes in the Upper Rhône River and its floodplain
Authors: JUGET JACQUES , LAFONT MICHEL
Published: May 2006

This paper summarizes twenty years of ecological research on aquatic oligochaetes of the Upper Rhône River and its alluvial floodplain (France). Species traits of fifty species of the ninety taxa recorded from two areas Gons and Brégnier‐Cordon) were used to examine the relationships among species traits, habitat utilization of these species, whether a relationship exists between species traits and habitat utilization, and the applicability of predictions from the river habitat templet and the patch dynamics concept in the framework of spatial and temporal habitat variability. We used fourteen habitat types and sixteen species traits in this analysis.

When examined by correspondence analysis, species traits separate the Naididae (with a higher potential for reproduction, small size, high mobility, and opportunistic diet) from all other families.

Habitat utilization by oligochaetes demonstrates two gradients: a vertical gradient that arranges species by their affinity for interstitial habitats (stygophily) and a transversal gradient that arranges them by their affinity for main channel habitats (rheophily).

No significant relationship was found between species traits and habitat utilization in a co‐inertia analysis.

Trends observed for species traits within the framework of spatial‐temporal habitat variability show only minor agreement with predictions of the river habitat templet.

Species richness is generally higher in superficial and interstitial habitats that are permanently connected with the main channel, and peaks in the superficial parapotamons (backwaters that are permanently connected with the main channel) characterized by intermediate levels of spatial as well as temporal variability; this pattern only partially fits with predictions of the patch dynamics concept.
Theoretical habitat templets, species traits, and species richness: ostracods (Crustacea) in the Upper Rhône River and its floodplain
Authors: MARMONIER PIERRE , BODERGAT ANNE‐MARIE , DOLÉDEC SYLVAIN
Published: May 2006

Ostracods occurring at two sections of the Upper Rhône River, France, were examined to determine relationships among species traits, habitat utilization, the relationship between species traits and habitat utilization, and trends in species traits and species richness in the context of spatial and temporal variability of habitats. Twenty regularly sampled species were used in this study and fifteen species traits were considered.

Throe groups can be distinguished according to their species traits: group 1 has species of mixed sizes with high reproductive rates, short life span, spherical shape, long swimming bristles, low thigmotactism, and high resistance to desiccation; group 2 has medium‐sized species with low reproductive rates, long life span, low or no tolerance to desiccation, geometric (trapezoidal, triangular) or streamlined carapace shape, no swimming bristles, and a strong thigmotactism; group 3 has the largest species with parthenogenetic reproduction, medium‐sized swimming bristles, and flattened or cylindric carapace shape.

Ostracod habitat utilization segregates the superficial and interstitial habitats along a gradient from the main channel to the abandoned arms and to the temporary waters.

The co‐structure (= relationship) between species traits and habitat utilization indicates that the species use particular habitats with a particular set of species trait modalities. Species with long life spans, late maturity, low fecundity, and low migratory ability are restricted to the interstitial habitats; the epigean species with long life spans, large size, and parental care are more abundant in permanent flowing and standing surface waters; the epigean species with short life spans, high migratory ability, and high tolerance to desiccation are more abundant in temporary ponds.

The analyses of the distribution of the species traits in a river habitat templet of spatial and temporal variability emphasized that the main disturbance structuring the Rhône River ostracod assemblage is desiccation.

Of the trends predicted for species traits in the framework of the river habitat templet, five (size, body form, attachment, reproductive technique, and mobility) are clearly opposite for ostracods (because the predictions were mainly established for flood‐related disturbances) but four (life span, number of reproductive cycles per year, age at first reproduction, and desiccation tolerance) are in agreement.

No trends in ostracod species richness in the framework of spatial–temporal habitat variability were evident.
Theoretical habitat templets, species traits, and species richness: amphibians in the Upper Rhône River and its floodplain
Authors: JOLY PIERRE , MORAND ALAIN
Published: May 2006

The purpose of this study was to test predictions of the habitat templet and the patch dynamics concept by analysing the relationship between either the species traits or species richness of amphibians and the spatial–temporal variability of eight habitat types of the Upper Rhône River and its floodplain, France.

The information on species traits of the twelve amphibian species was accumulated primarily from the literature; that on habitat utilization was based on field surveys. The information was ‘fuzzy coded’, analysed by ordination techniques, and finally linked to the spatial–temporal variability of habitat types elaborated elsewhere in this issue.

After elimination of the variance caused by the differences between urodeles and anurans, correspondence analysis of the matrix of species traits demonstrated that the flexibility of the temporal pattern of reproduction was the major source of variation among amphibian species. A less significant source of variation within anurans was related to traits usually linked to the concept of r–K selection (potential number of descendants per reproductive cycle and ratio of egg size to female size).

A correspondence analysis of habitat utilization by amphibian species separated four groups of habitat types, corresponding to different degrees of influence that the active channel had on adjacent waters in the floodplain (i.e. from habitats that are most frequently disturbed by floods, to habitats of braided sections, old oxbow lakes, and the more terrestrialized habitats).

A co‐inertia analysis of the relationship between species traits and habitat utilization separated two habitat types (terrestrialized former meanders and oxbow lakes) from the others. Species of terrestrialized habitats had a reproductive display, a low number of descendants per reproductive cycle, and a high ratio of egg size to female size. Species of oxbow lakes were early or synchronous breeders, and laid a single clutch.

Neither the predictions of the habitat templet concept nor those of the patch dynamics concept were validated. Species traits were not significantly correlated to the axes of the spatial–temporal variability templet. The highest species richness was observed in habitat types with the highest temporal variability; in addition, richness did not peak at highest spatial variability.

Deviation from the predictions of the river habitat templet could be explained by: (i) the over‐simplification of this model with regard to the evolution of the complex life cycles of the amphibians; and (ii) an underestimation of the importance of phylogenetic constraints and the evolution of community interactions.
Native and exotic freshwater fishes in Spanish river basins
Authors: ELVIRA B.
Published: May 2006

1. The degree to which fish faunas have been invaded by exotic species is quantified on the basis of river basins.

2. Nineteen exotic species are now established in Spanish fresh waters. Alburnus alburnus (L., 1758) is reported here for the first time.

3. The native/total fish ratio varies from 0.71 in Galicia, the best preserved fish fauna, to 0.41 in Douro, the most modified fish assemblage. The national average ratio (0.63) is similar to that reported for Portugal (0.65), but higher than that in Italy (0.56) and much lower than that in Greece (0.88).

4. Exotic fishes have sometimes become successfully established over wide areas in a short time.
Freshwater amphipods as biomonitors of metal pollution in surface and interstitial aquatic systems
Authors: PLÉNET S.
Published: May 2006

1. The relationships between levels of metals (Zn, Cu) in the environment (water, sediment) and in the tissues of three species of amphipod crustaceans were investigated in superficial and interstitial ecosystems of the Rivers Rhone and Ain, France.

2. Epigean and hypogean amphipods differed in their ability to accumulate Zn and Cu. At all sites, Gammarus fossarum (epigean) showed lower Zn or Cu body concentrations than Niphargus of, rhenorhodanensis or Niphargopsis casparyi (hypogean). Differences were also observed between the two interstitial taxa.

3. A significant difference among sites was observed for metal concentrations in sediment. In contrast, no significant inter‐site differences were found for metal concentrations in organisms.

4. No significant correlation was found between metal concentrations in the three taxa and quantities of metals in the water. A positive correlation was observed between Zn and Cu body content in Gammarus fossarum and metal level in the sediment. No relationships were found between interstitial amphipods and metal concentrations in the sediment.

5. Differences in accumulation rates among the three amphipod species suggest their potential use as biological indicators for monitoring metal pollution.
The contribution of flood disturbance, catchment geology and land use to the habitat template of periphyton in stream ecosystems
Authors: BIGGS BARRY J.F.
Published: May 2006

1. Periphyton chlorophyll a (chl a), ash‐free dry mass, taxonomic composition, and cellular and water‐column nutrients were analysed every 4 weeks for a year at sixteen stream sites in New Zealand. The hypothesis was investigated that broad‐scale differences in mean monthly periphyton development are defined primarily by the frequency of flood disturbances and the periphyton's interaction with the nutrients. it us of the streams as determined by catchment geology and land use.

2. Overall, mean monthly chl a concentration declined with increasing flood frequency (r= ‐0.711, P < 0.001), and seasonality in chl a was better defined at sites with a low frequency of floods. Chlorophyll a concentration was generally low throughout the year at sites with frequent floods (> 15 yr−1).

3. No relationship existed between inorganic nutrient concentrations and catchment geology or land development. However, conductivity declined significantly as a function of the percentage of the catchment underlain by nutrient‐poor, hard rocks (plutonic and fine‐grained metamorphic rocks) (r= ‐0.515, P < 0.05), but increased significantly with the percentage of the catchment in intensive agricultural land use (r= 0.799, P < 0.001).

4. Cellular nutrient concentrations suggested that nitrogen was the nutrient most commonly limiting periphyton production. In turn, cellular N concentrations declined significantly with increasing percentage of the catchment in hard rock (r= ‐0.5M, P < 0.05) and increased with percentage of the catchments in intensive agricultlural land use (r= 0.948, P < 0.001).

5.The sites were classified into three enrichment groups (high, moderate and low) based on their land use and underlying geology. Cellular N concentrations varied significantly among these enrichment groups (ANOVA F= 14.661, P < 0.001).

6. Log chl a decreased significantly with increases in the annual 80th percentile velocity. However, the relationship was significantly different among the enrichment groups.

7. A stepwise multiple regression on the full dataset identified that the frequency of floods, proportion of the catchment in high‐intensity agricultural land use and proportion in alkaline rocks were the most significant factors explaining variation in mean monthly chl a among the sites (r2= 89%).

8. Overall, the results showed that flood disturbance and catchment enrichment regimes are probably the principal axes of the habitat template of periphyton among the study streams, and could be used to explain and predict broad‐scale differences in periphyton development among other temperate stream ecosystems.
The ordination of benthic invertebrate communities in the South Platte River Basin in relation to environmental factors
Authors: TATE C.M. , HEINY J.S.
Published: May 2006

1. Spatial patterns of benthic‐invertebrate communities were examined in the 62 900 km2 South Platte River Basin in Colorado, Nebraska and Wyoming, U.S.A., to determine major environmental factors associated with invertebrate distribution. Stable substrates were sampled semiquantitalively for invertebrates from 27 July to 7 August 1992, at twenty‐one sites. Data on physical and chemical variables were collected concurrently at each site.

2. Four site groups were identified using derrended correspondence analysis (DCA), one in the mountains and three in the plains (braided channels, tributaries near the confluence with the main stem, and sites affected by effluent from wastewater‐treatment plants). DCA axis 1 separated sites into the two major ecoregions (Southern Rocky Mountains and Western High Plains), and regression of DCA axis 1 with environmental variables indicated significant relationships primarily with slope, water temperature, specific conductance, and concentrations of organic nitrogen + ammonia and total phosphorus in surface water. Regression of DCA axis 2 with environmental variables indicated significant relationships with channel width and concentrations of nitrate + nitrite in surface water.

3. Invertebrate community composition and structure varied between ecoregions with greater number of taxa and number of insect families in mountain streams than in plains streams. Within an ecoregion, land use affected the invertebrate community.

4. Factors affecting invertebrate community distribution in stream ecosystems are scale dependent.
Long‐term dynamics of a freshwater sponge population
Authors: PRONZATO ROBERTO , MANCONI RENATA
Published: May 2006

1. Quantitative field data were collected from a Sardinian population of the sponge Ephydutia fluvtatilis from 1987 to 1993 in order to study its life style.

2. Growth of sponges was high during the annual cycle, and showed few changes in 6 years. Gemmulation was very rapid and highly efficient. Life spans of many specimens extended up to 5 years.

3. The population was destroyed by one flood during our study period. The persistence of gemmules on substrata suggested that dispersal was low in our study population. Recolonization started 7 months after the flood and re‐established a new population, different from the previous one in terms of spatial structure and specimen size.
Effects of microspatial complexity on a herbivore—epilithon interaction in an Australian upland stream
Authors: GAWNE BENJAMIN , LAKE P. SAM
Published: May 2006

1. Increases in spatial heterogeneity may provide more food, create new resources or interfere with the foraging activities of a herbivore.

2. Three colonization experiments were performed in an upland stream to investigate the effects of one type of spatial heterogeneity (grooves on the substratum) on the relationship between an abundant herbivore, Agapetus monticolus (Banks, Trichoptera), and the epilithon on which it feeds.

3. The results indicate that grooves do not provide any different resources or interfere with the foraging activities of A. monticolus, but may increase food abundance, although the effect of grooves on food abundance appears to vary temporally.

4. Temporal variation in the effects of microspatial complexity raises the possibility that its importance to the community may be over‐ or underestimated unless experiments are designed to incorporate this temporal variation.
Randomness and aggregation: analysis of dispersion in an epiphytic chironomid community
Authors: TOKESHI MUTSUNORI
Published: May 2006

1. Patterns of dispersion in a chironomid community on the submersed macrophyte Myriophyllum spicatum were analysed.

2. Random dispersion commonly occurred throughout the year, with an average of 40% of all species being observed with random spatial patterns. The frequency of occasions with random dispersion varied among chironomid species, ranging from 3.3% in Rheotanytarsus curtistylus to 56% in Thienemanniella majuscula.

3. Estimates of the negative binomial parameter k show that 26% of all cases demonstrate strong aggregation (0 < k < 1.0) while nearly half (47%) have quasi‐random dispersion. Interspecific variation in k was not significant statistically when all the species were considered together, although a pairwise comparison between two abundant species Tvetenia calvescens and Rheotanytarsus curtistylus demonstrated a marginally significant difference. When different instars were compared, the percentage frequency of strong aggregation (0 < k < 1.0) declined from first instars (49%) to later instars (II‐38%, III‐24% and IV‐27%).

4. Variance/mean and m*—m regressions (m* is Lloyd's mean crowding statistic and m is the sample mean) both fitted the data well, but there was little indication of significant interspecific variation in parameter values, particularly the slope of regression.

5. Dispersion patterns were examined along with the analysis of spatial overlap in this community. Forty‐two per cent of species‐pairs with reduced spatial overlap (spatially ‘segregated’ pairs) contained one or both species with random dispersion, while the corresponding value for spatially unsegregated pairs was 57%. This suggests that spatial segregation is not necessarily caused by strong, independent aggregation of both species. Comparing spatially segregated vs. unsegregated pairs, the former tend to have one species with a stronger tendency of aggregation than species of the latter.

6. Patterns of dispersion observed were considered in the light of ‘random patch formation’. Random patch formation emphasizes the stochasticity of patch‐forming processes as well as the stochastically dynamic nature of resultant patches. Unlike terrestrial drosophilid assemblages, where strong aggregation is a predominant pattern, this chironomid community demonstrates widely varying degrees of dispersion with high occurrence of randomness, reflecting the stochasticity of dispersal and recolonization processes. It is suggested that, in terms of species coexistence, more emphasis should be placed on stochasticity rather than on aggregation in this type of community.
Phenotypic variation in metamorphosis in four species of freshwater copepods
Authors: TWOMBLY S.
Published: May 2006

1. Physiological metamorphosis accompanied by an ecological habitat shift is a widespread life‐history phenomenon, and both age and size at metamorphosis are highly variable in many organisms. In this study, age and size at metamorphosis (defined as the transition from the last naupliar to the first copepodite stage) were quantified for four species of freshwater copepods to determine the scale on which these two traits vary, if age and size at metamorphosis are equally variable, and if variation at metamorphosis is related to variation in newborn size.

2. Measurements of laboratory‐reared and field‐caught individuals show that age and size at metamorphosis, together with newborn size, vary among siblings, between families within a population, between populations of one species and between closely related species.

3. In all populations, age at metamorphosis was the most variable trait, a result observed in many other organisms. Most of the variation in age at metamorphosis could be explained by differences between families within a population, while differences among siblings from the same clutch accounted for most of the variation in size at metamorphosis.

4. Although newborn size was variable, differences in this trait could not fully account for variation observed at metamorphosis. Newborn size differed among populations, but most interpopularional differences disappeared by the rime metamorphosis was reached. In particular, size at metamorphosis appears to be tightly constrained in freshwater copepods.

5. Age and size at metamorphosis were not equally variable among species, either. Species‐specific metamorphic envelopes (joint distributions of age and size at metamorphosis) result from differences in trait means, variances and covariances, and suggest very different larval growth trajectories among three of the species examined.
Life cycles and food habits of mayflies and stoneflies from temporary streams in western Oregon
Authors: DIETERICH MARTIN , ANDERSON N. H.
Published: May 2006

1. Field data and results from laboratory rearing are combined to describe life cycles and food habits of the mayflies Paraleptophlebia gregalis and Ameletus n. sp., and the stoneflies Soyedina interrupts, Ostrocerca foersteri, Sweltsa fidelis and Calliperla luctuosa.

2. P. gregalis, A. n. sp., S. interrupts and O. foersteri have univoltine life cycles which are characterized by a high degree of plasticity. S. fidelis and C. luctuosa have semivoltine life cycles which are more tightly synchronized.

3. Laboratory feeding trials and field observations characterize P. gregalis as a collector, A. n. sp. as a scraper, O. foersteri and S. interrupta as shredders and C. luctuosa as a predator mainly of midge larvae. Late‐instar larvae of S. fidelis are believed to be scavengers.

4. Laboratory rearing yielded a negative correlation between growth rates (Y) and larval size in autumn (X) for S. interrupta. This indicates compensatory growth by small larvae in order to achieve synchronized emergence. The correlation can be described by the equation: Y = 0.0053–0.0036X (R2= 0.82; P < 0.01; n = 22)

5. The field and laboratory data indicate that photoperiod mainly determines the rate of development and size of emerging subimagos in P. gregalis.
Experiments on the effects of food and density on voltinism in a stream‐dwelling water strider (Aquarius remigis)
Authors: TRAMONTIN A.D. , SIH A.
Published: May 2006

1. The stream water strider Aquarius remigis shows a latitudinal pattern of variation in voltinism. In general, populations with shorter growing seasons (e.g. in eastern Canada) tend to be univoltine (animals that reach adulthood in the summer overwinter before reproducing in the following spring), whereas populations with somewhat longer growing seasons (e.g. in the north‐eastern United States) tend to be bivoltine.

2. This pattern was broken at our study site in the south‐eastern United States (Kentucky) where A. remigis had a long growing season, but was almost always univoltine. In summer 1993, however, adult A. remigis in central Kentucky displayed a bivoltine reproductive cycle; i.e. individuals in some pools began breeding shortly after maturing to the adult stage.

3. A field survey documented a negative relationship between local water strider density and reproductive activity in prediapause adults. A laboratory experiment manipulating food availability and density, revealed that animals held at low density with high food levels displayed greater mating activity and egg production than did their counterparts at higher density or lower food levels.

4. A laboratory experiment also showed that high water strider density resulted in a greater frequency of very short pair durations (< 10 min).

5. Although the observed effects of density and food availability on mating activity of prediapause adults seem intuitively reasonable, they differ from the patterns observed in overwintered adults. The difference in reproduction patterns might be due to differences in selective pressures on prediapause vs. post‐diapause adults.
Response of epilithic diatom assemblages to water pollution in rivers in the Tokyo Metropolitan area, Japan
Authors: LOBO EDUARDO A. , KATOH KAZUHIRO , ARUGA YUSHO
Published: May 2006

1. During the spring of 1992, fifty‐two quantitative diatom samples were collected from twenty‐eight rivers located in the Tokyo Metropolitan area, Japan, to study the response of the diatom assemblages to water pollution (assessed using physical and chemical data determined monthly from April 1987 to March 1992).

2. Species composition was analysed by means of biotic indices (Pantle and Buck's saprobic index) and multivariate analyses [two‐way indicator species analysis (TWINSPAN) for classification and canonical correspondence analysis (CCA) for ordination]. Species‐abundance relationships were analysed using diversity indices (species richness, Shannon's diversity index and Pielou's evenness index) and rank‐abundance patterns (rank‐abundance curves).

3. CCA revealed two major gradients. The first corresponded to organic pollution and eutrophication. The second corresponded to variables related to geographical location. Four main station groups were determined by TWINSPAN. The location of the indicator species of groups 1–3 along the CCA axis 1 is consistent with their known pollution tolerance characteristics. Indicator species for group 4 had larger scores on CCA axis 2, and are representative of brackish water environments.

4. Species richness tended to be higher in the intermediate range of water pollution. Pielou's evenness index and Shannon's diversity index followed the same tendency but only weakly.

5. The rank‐abundance patterns of diatom assemblages were more or less constant in all stations. The curves were very similar in shape, differing only in length and gradient (directly related to species richness and evenness, respectively).

6. The results of this study indicate that the response of diatom assemblages to environmental change can be observed in species compositional variation. Multivariate analyses and pollution indices revealed this response and are to be preferred to species diversity measures.
Structure, development and induction of a new diapause stage in rotifers
Authors: GILBERT JOHN J.
Published: May 2006

1. This study shows that females of Synchaeta pectinata Ehrenberg can produce two morphologically and physiologically distinct kinds of amictic eggs that develop parthenogenetically into females. One kind, until now the only one known in monogonont rotifers, is a thin‐shelled (about 1.4 μm) subitaneous egg that develops without arrest. The other kind is a thick‐shelled (about 9 μm) egg that enters obligatory diapause after 1–3 cleavage divisions before resuming development. The thicker shell of the diapausing egg is due to an expansion of the outer sublayer of the single‐layered shell.

2. The mean duration of the diapause at 19 °C (L : D 16 : 8) is about 14 days. This diapause is not broken by low temperature (5 °C), and it is not greatly extended by storage at low temperature (5 °C).

3. Diapausing eggs are induced immediately after a brief starvation period, and seem to be produced at no additional energetic cost. However, a population producing a high proportion of diapausing eggs has a much reduced reproductive potential.

4. Production of diapausing amictic eggs may be a strategy to increase the ability of clones to survive food limitation.

5. Diapausing amictic eggs differ markedly from fertilized resting eggs produced following bisexual reproduction during favourable conditions.
Size‐related shifts in the physical habitat of two mayfly species (Ephemeroptera)
Authors: BUFFAGNI ANDREA , CROSA GIUSEPPE , MARCHETTI ROBERTO
Published: May 2006

1. The spatial niche shifts of the nymphs of two mayfly species (Rhithrogena semicolorata and Ecdyonurus sp, gr. venosus) in relation to their growth were investigated in two lowland springs of northern Italy where they are dominant species.

2. Ordination of the different size classes of the two species revealed a canonical trend related to season and bottom roughness.

3. Larger nymphs of both species colonized rougher substrata. Differences between species in the roughness of areas colonized by small nymphs, which were very numerous, may have been due to competition for space.
Biofilm development and invertebrate colonization of wood in four New Zealand streams of contrasting pH
Authors: TANK JENNIFER L. , WINTERBOURN MICHAEL J.
Published: May 2006

1. Biofilm development and activity on wood substrata (Nothofagus menziesii) were examined at four forested sites in a South Island, New Zealand, river catchment over a period of 6 months. Two of the sites had brown waters and mean pH of 3.7 and 4.5, whereas the other two had clear waters and mean pH of 6.3 and 6.8.

2. Fungi and other filamentous heterotrophs were the dominant colonizers of wood at all sites; few algal cells were present. Incorporation of 14C‐glucose by biofilms was greatest in all four streams after 3 months, whereas endocellulase activity fluctuated over time and temporal patterns differed among streams.

3. No clear relationship was found between the incorporation of 14C‐glucose or endocellulase activity of biofilms and pH, although at one near‐neutral pH site 14C‐glucose uptake increased in response to nutrient (N + P) additions.

4. After 6 months, incorporation of 14C‐glucose and endocellulase activity of biofilms on Pinus radiata dowels buried vertically in the stream beds did not differ at depths of 3–9 cm and 19–25 cm in each stream.

5. Radiotracer experiments with a grazing amphipod (Paraleptamphopus sp.) demonstrated that biofilms on wood from all four sites could be ingested and at least partially assimilated. Chironomid larvae and harpacricoid copepods were the most abundant invertebrates colonizing wood substrata at all sites. Different chironomid species dominated at acidic and near‐neutral pH sites.

6. Overall, our findings provide little support for the hypothesis that microbial activity on organic substrata is necessarily lower in streams of low pH.
Microbial enzyme activities as indicators of organic matter processing rates in a Lake Erie coastal wetland
Authors: JACKSON COLIN R. , FOREMAN CHRISTINE M. , SINSABAUGH ROBERT L.
Published: May 2006

1. Particulate organic material (POM) is an important source of energy and nutrients in aquatic ecosystems. The decomposition of this material is typically studied using the litter bag technique. However, this method has inherent limitations that can preclude the estimation of in situ decomposition rates, especially for fine particles. In this study, we tried to circumvent these limitations through the use of enzymatic decomposition models (EDMs), which relate mass loss rates to lignocellulase activities. With this approach, we investigated the in situ processing of three size ranges of detritus in a Typha wetland.

2. Litter was collected, dried and sorted into three size ranges [coarse (C) > 4, medium (M) 0.5–4 and fine (F) 0.063–0.5 mm] and placed in litter bags that were attached to the sediment surface at two sites in a Typha wetland in May 1994. Over a 7‐month period, litter bags were collected and analysed for mass loss and the activities of six extracellular enzymes involved in the degradation of lignocellulose. In situ POM was collected concurrently, sorted into the same three size ranges and assayed for the same suite of enzymes. Additional cores were taken for the determination of organic matter standing stocks and particle size distribution.

3. Mean mass loss rates for CPOM, MPOM and FPOM were ‐0.139, ‐0.073 and ‐0.053% day−1, respectively. Only CPOM rates were significantly different between sites. For CPOM and FPOM there were strong linear relationships between mass loss and cumulative enzyme activities; the mass loss data for MPOM were erratic and precluded the development of reliable enzyme models. EDMs for CPOM and FPOM were constructed from regressions relating mass loss to average cumulative lignocellulase activity, and used to estimate instantaneous in situ decomposition rates. These rates varied by site and throughout the year but averaged ‐0.204 and ‐0.045% day−1, respectively. Based upon measurements of OM standing stock and particle size distributions, POM processing rates of 1100–1400 g m2 yr−1 were calculated. These rates are near the upper end of the range for net annual production in Typha wetlands, suggesting that there is little net accumulation of POM.

4. Despite some problems, the EDM method has the potential to facilitate studies of detrital dynamics in large, heterogeneous systems.
Variability of invertebrate herbivory on the submerged macrophyte Potamogeton perfoliatus
Authors: JACOBSEN DEAN , SAND‐JENSEN KAJ
Published: May 2006

1. Invertebrate herbivory was studied in twenty‐eight populations of the submerged macrophyte Potamogeton perfoliatus in Danish streams and lakes in mid‐June. All populations but one experienced invertebrate herbivory and loss ranged from 0 to 11.9% of leaf area among populations. Loss generally increased with leaf age towards the base of the plants, and young apical leaves were rarely damaged.

2. Herbivory loss was significantly higher in streams (mean 5.0%) than in lakes (mean 2.2%), but varied greatly among populations within the same stream or lake and was not correlated to physico‐chemical site characteristics, size or density of plant population, or leaf N and P content. High levels of invertebrate herbivory were therefore not associated with certain types of streams or lakes.

3. High herbivore biomass relative to abundance of plants was conducive to high loss. In streams, the biomass of the trichopteran Anabolia nervosa accounted for 50% of the variability in loss. No single species appeared to be equally important in lakes, although loss was correlated to the biomass of the chrysomelid beetle Macroplea appendiculata. Obligate herbivores, such as lepidopteran larvae, apparently exerted little damage on P. perfoliatus, and leaf mining and channelization from specialist feeders were negligible. It is concluded that shredders acting as facultative herbivores were the most important invertebrate herbivores on P. perfoliatus in Danish freshwaters.
Suppression of microzooplankton by zebra mussels: importance of mussel size
Authors: MACISAAC HUGH J. , LONNEE CHRISTOPHER J. , LEACH J.H.
Published: May 2006

1. The zebra mussel (Dreissena polymorpha) is amongst the most recent species to invade the Great Lakes. We explored the suppressive capabilities of mussels 6–22‐mm in size on Lake St Clair microzooplankton (< 240)μm) in laboratory experiments.

2. Absolute suppression of rotifers and Dreissena veliger larvae was proportional to mussel shell length for individuals larger than 10 mm; larger zooplankton, mainly copepod nauplii and Cladocera, were not affected. Mussel clearance rates on rotifers generally exceeded those on veligers, although rates for both increased with increasing mussel size. Rotifer‐based clearance rates of large (22 mm) mussels approached published values for phytoplankton food.

3. Most zooplankton taxa, particularly rotifers, declined significantly in western Lake Erie during the late 1980s concomitant with the establishment and population growth of zebra mussels in the basin. Densities of some taxa subsequently increased, although rotifers and copepod nauplii densities remained suppressed through 1993. Available evidence indicates that direct suppression by Dreissena coupled with food limitation provides the most parsimonious explanation for these patterns.
Benthic macroinvertebrate community structure, function and production with respect to habitat type, reach and drainage basin in the southern Appalachians (U.S.A.)
Authors: WOHL DEBRA L. , WALLACE J. BRUCE , MEYER JUDITH L.
Published: May 2006

1. Benthic macroinvertebrates were sampled for 1 year to assess functional and taxonomic differences in invertebrate biomass and production with respect to habitat types, reaches and catchments in Wine Spring Basin, western North Carolina. Quantitative samples were collected from depositional, cobble‐riffle and bedrock outcrop habitats at four stream reaches (two headwater sites, one second order, and one third order). Other measures included physical parameters, periphyton and organic matter standing crops. Invertebrate data from the Wine Spring catchment were also compared with data from another catchment (Ball Creek) within the same region.

2. The three habitat types had different current velocities and mean substratum particle sizes; both measures were greatest in bedrock outcrop habitats and lowest in depositional habitats. Organic matter standing crops, invertebrate functional group productivity and biomass also differed significantly with respect to habitat type. Cobble‐riffle areas had the lowest standing crops of organic matter, invertebrate productivity and biomass.

3. Both invertebrate communities and organic matter standing crops differed significantly between the two headwater reaches. First‐ to third‐order reaches differed in taxonomic composition at the genus level, yet had similar relative functional group productivity and biomass.

4. Annual mean invertebrate biomass and secondary production were greater in the Wine Spring Basin than in Ball Creek. Sites in both the Wine Spring and Ball Creek catchments, however, exhibited similar functional group distributions per habitat type.

5. Local geomorphology and related physical parameters influenced the structure of invertebrate functional group composition, and the distribution of organic matter standing crops. Furthermore, comparison of community structure in Wine Spring with that in Ball Creek suggested that taxonomic composition was more related to catchment‐specific parameters (e.g. thermal regime, evolutionary history) than stream size.
An extraordinary reproductive strategy in freshwater bivalves: prey mimicry to facilitate larval dispersal
Authors: HAAG WENDELL R. , BUTLER ROBERT S. , HARTFIELD PAUL D.
Published: May 2006

1. Females of the North American freshwater bivalve Lampsilis perovalis release their larvae, which are obligate parasites on fish, in a discrete mass (superconglutinate) resembling a small fish in shape and coloration. After release, the mass remains tethered to the female by a long, transparent, mucous strand and, in stream currents, displays a darting motion that further mimics a small fish.

2. Release of superconglutinates was observed in March and April at water temperatures of 14–17 °C. However, superconglutinates detached from the parent mussel were observed from March to June at water temperatures of 11–26 °C, indicating that release may occur into the summer.

3. The superconglutinate lure may function to attract a predaceous fish to ingest the mass, ensuring that the larvae are exposed to a suitable host.

4. This reproductive strategy was confirmed recently to occur in a congener, L. subangulata and is suspected to occur in another congener, L. australis.
The effects of group size on per capita ingestion in flatworms
Authors: CASH KEVIN J. , WRONA FREDERICK J. , SCRIMGEOUR GARRY J.
Published: May 2006

1. We evaluated the effect of group size on the per capita ingestion rates of three species of flatworm, two of which actively group with conspecifics (Dugesia tigrina, D, dorotocephala) and employ mucus to capture prey, and a third species (Mesostoma ehrenbergii) that does not actively group but does use mucus to capture prey.

2. As flatworm group size increased, daily per capita ingestion first increased and then decreased for D. tigrina and D. dorotocephala. In the case of D. tigrina this pattern was observed even at low predator densities. Ingestion rates of M. ehrenbergii were largely unaffected by group size.

3. Results suggest that the observed changes in per capita ingestion rates with changes in group size previously reported for D. tigrina are related to their tendency for active grouping and are not directly a consequence of prey capture technique or experimental design.

4. We argue that freshwater triclads in general, and D. tigrina in particular, represent an ideal model system for the development and testing of group foraging theory.