bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

SUMMARY1. 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

SUMMARY1. 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

SUMMARY1. 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

SUMMARY1. 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

SUMMARY1. 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

SUMMARY1. 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

SUMMARY1. 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

SUMMARY1. 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

SUMMARY1. 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

SUMMARY1. 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

SUMMARY1. 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.
Effect and potential ecological significance of the interaction of humic acids with two aquatic extracellular proteases
Authors: DUDLEY RICHARD J. , CHURCHILL PERRY F. 
Published: May 2006

SUMMARY1. The effects of humic acids and fulvic acids on an extracellular serine and metalloprotease purified from a strain of Aeromonas hydrophila isolated from a freshwater wetland were examined. The serine protease was inhibited by humic acids at pH and humic acid concentrations found naturally in the wetland where this strain of A. hydrophila was isolated. The metalloprotease was not inhibited by humic acids at any pH investigated. Fulvic acids had no effect upon either protease.2. Inhibition of serine protease activity by humic acids was reversed by increasing the pH to 9, as well as increasing the ionic strength by addition of CaCl2‐ It was concluded that the interaction between humic acids and the serine protease was primarily ionic.3. The formation of a humic acid‐serine protease complex increased the half‐life of enzymatic activity in dilute solutions. Humic acids had no effect on the stability of the metalloprotease.4. There was no clear effect of humic acids on the growth of A. hydrophila, indicating that either the serine protease is not involved in the rate‐limiting step of growth or that sufficient activity exists even when the serine protease is inhibited by humic acids.5. Increasing the enzymatic lifetime through association with humic acids may be an adaptive mechanism which could result in energy conservation due to a decreased requirement for protein synthesis.
Variation in reproductive characteristics of colonies of the freshwater bryozoan Cristatella mucedo
Authors: UOTILA LAURA , JOKEL JUKKA 
Published: May 2006

SUMMARY1. We studied relationships between different forms of reproduction and local variation in the reproductive state of colonies of a common freshwater bryozoan Cristatella mucedo Cuvier (Bryozoa: Phylactolaemata). Four sampling locations in central Finland, including both lotic and lentic habitats, were sampled by scuba diving. The traits studied were occurrence of sexual larvae, colony size, number of resting stages (statoblasts) and number of zooids.2. While 76.9% of the sampled colonies carried statoblasts at the time of sampling, only 4.5% of the colonies were brooding sexual larvae. Most of the colonies were relatively small with a mean colony size of 16.6 mm.3. In colonies brooding larvae, the number of statoblasts was positively correlated with the number of larvae. We did not detect a colony size threshold for sexual reproduction or formation of statoblasts. Colonies carrying statoblasts had a lower number of zooids per unit dry weight.4. We found significant variation in reproductive traits of colonies among the sampling locations, and among lotic and lentic habitats. The observed phenotypic differences may reflect broadly distributed, phenotypically plastic clones. Differences in clonal composition of local populations cannot, however, be ruled out and factors that may provide clonal diversity are discussed.
How do predator‐induced changes affect prey vulnerability? Larvae of Chaoborus flavicans (Diptera: Chaoboridae) feeding on Daphnia pulex (Crustacea: Cladocera)
Authors: LÜNING JULIA 
Published: May 2006

SUMMARY1. The relative food consumption and prey preferences of fourth‐instar larvae of the phantom midge Chaoborus flavicans were investigated in laboratory experiments. Neonates and second instars of two clones of the cladoceran Daphnia pulex ‐ an Arctic and an European clone ‐ were offered to the predatory larvae. Each clone was divided into two groups: one group was exposed to the midge larvae during embryogenesis, whereas the other was not exposed to the predator.2. While both exposed and unexposed neonates of the European clone had neck teeth, animals of the Arctic clone did not develop these spines.3. A consistent rank order was observed in the vulnerability of the four prey types. Newborn daphnids from the Arctic clone were more vulnerable to predation than those from the European clone. Moreover, differences existed within each clone, regardless of neck teeth induction: Daphnia previously exposed to Chaoborus were less susceptible to the predators than unexposed prey.4. The results show differences in the vulnerability of exposed and unexposed neonates that are not caused by the presence or absence of neck teeth. Perhaps the reduced vulnerability of exposed neonates was due to predator‐avoidance behaviours.
A hierarchical study of macroinvertebrate recolonization of disturbed patches along a longitudinal gradient in a prairie river
Authors: JOHNSON S.L. , VAUGHN C.C. 
Published: May 2006

SUMMARY1. Macroinvertebrate densities and community composition were examined at three spatial scales after substratum disturbance; among reaches along a longitudinal gradient, within reaches and within plots. Reaches consisted of sandstone outcrops that were separated by approximately 2 km of highly mobile sandy silt substratum.2. Substrata were disturbed by scraping sandstone plots (0.3 ± 0.3 m). Body‐sized depressions created by Trichoptera in the sandstone were removed along with the upper 5 mm of sandstone, resulting in areas of newly exposed, smooth sandstone.3. The spatial scale of examination determined whether patterns of macroinvertebrate distribution and densities were discernible. Initially there were no significant differences in community composition or total densities among reaches or among upstream/ downstream locations within reaches. Following substratum disturbance and 30 days recolonizarion, total macroinvertebrate densities did not differ significantly between undisturbed plots and disturbed plots. However, densities of Petrophilia (Pyralidae: Lepidoptera) differed along the longitudinal gradient and the Simuliidae had its highest density in the upstream reach. Significant differences were found in total macroinvertebrate densities between the upstream and the downstream halves of disturbed plots, with higher densities occurring in the downstream portions.4. Recolonized plots had similar macroinvertebrate densities and community composition to undisturbed plots, suggesting that the stream community was highly resilient.