bluuebunny/crossref_metadata_2025_split huggingface dataset:
Selective foraging by the crayfish Orconectes virilis and its impact on macroinvertebrates
Authors: HANSON JOHN MARK , CHAMBERS PATRICIA A. , PREPAS ELLIE E. 
Published: May 2006

SUMMARY. 1. The impact of crayfish predation on the abundance of macroinvertebrates was examined under semi‐natural conditions. Female (Experiment 1) or male (Experiment 2) crayfish (Orconectes virilis) were held for 5 weeks in twelve small pools (4.67 m2 surface area) at biomasses of 0. 5, 10 or 18 g m−2 (live weight). The pools were stocked with known densities of macroinvertebrates.2. Crayfish significantly affected the abundance of macroinvertebrates in the pools. Differences in the effects of crayfish on macroinvertebrates were related to crayfish sex, the presence of age‐0 crayfish, and the species of macroinvertebrate.3. The abundance of snails (Stagnicola elodes and Physa gyrina) was greatly reduced, in comparison with controls, by biomass of female crayfish ≥10 g m−2 and by biomasses of male crayfish ≥5 g m−2. The total density of non‐molluscan invertebrates was inversely correlated with the biomass of female crayfish but the total biomass of non‐molluscan invertebrates did not differ between treatments. This is consistent with our observation that small invertebrates (<2 mg wet weight) were less numerous, and large amphipods (32–64 mg) were more numerous, in pools stocked with female crayfish. In contrast, male crayfish had little apparent effect on the abundance of non‐molluscan invertebrates.4. Age‐0 crayfish hatched at the end of Experiment 1 and were present in each pool at the start of Experiment 2. Surprisingly, male crayfish preyed little on age‐0 crayfish. At the end of Experiment 2, the densities of age‐0 crayfish varied between six and 116 individuals m−2 and there was a strong inverse correlation between the mean biomass and density of age‐0 crayfish recovered from the pools. This suggests age‐0 crayfish were food limited in the pools and may explain the dominance of oligochaetes (which largely escape predation by burrowing) in the invertebrate community at the end of Experiment 2.5. These results indicate that even relatively low densities of crayfish could greatly affect the abundance of macroinvertebrates in lakes. The introduction of crayfish into lakes (most lakes in Alberta currently have no crayfish) could substantially affect abundance and species composition of the macroinvertebrate community and, ultimately, the fish populations.
Germination requirements and seed banks of some nymphaeid macrophytes: Nymphaea alba L., Nuphar lutea (L.) Sm. and Nymphoides peltata (Gmel.) O. Kuntze
Authors: SMITS ANTONIUS J. M. , VAN AVESAATH PIM H. , VAN DER VELDE GERARD 
Published: May 2006

SUMMARY.

Germination experiments demonstrated that the innate dormancy of the seeds of Nymphaea alba L., Nuphar lutea (L.) Sm. and Nymphoides peltata (Gmel.) O. Kuntze could be overcome by a cold treatment. Light stimulated the germination of the three species. Hypoxic conditions stimulated the germination of Nymphaea alba and Nuphar lutea seeds but the seeds of Nymphoides peltata did not germinate under these conditions.
Experimental seed banks of Nymphaea alba, Nuphar lutea and Nymphoides peltata were laid out in three water bodies, varying in pH and alkalinity. Germination patterns indicated that Nymphaea alba and Nuphar lutea produce transient seed banks, but that Nymphoides peliata produces a persistent seed bank. Sampling of natural seed banks and subsequent germination tests were in concordance with the results of the seed bank experiment.
The experimental above‐ground seed banks of Nymphaea alba, Nuphar lutea and Nymphoides peltata showed similar germination patterns in the three selected water bodies, despite the differences in pH and alkalinity between them. However, the distribution of Nymphoides peliata is restricted to well‐buffered waters, so that its absence from soft and acid water bodies must be due to post‐germination mechanisms and/or processes.
In aquatic systems where Nymphoides peltata co‐exists with the other nymphaeid species studied, it is largely restricted to a bell between the helophytes and the vegetation at deeper sites. The deeper sites were dominated by Nuphar lutea and Nymphaea alba. Germination requirements and seedling emergence from buried seeds of Nymphaea alba, Nuphar lutea and Nymphoides peliata play an important role in the establishment of the zonation pattern of these nymphaeid macrophytes.
Concomitant diel vertical migration of a predatory leech and its amphipod prey
Authors: BLINN DEAN W. , DAVIES RONALD W. 
Published: May 2006

SUMMARY. The concomitant diet vertical migrations of the predaceous leechErpobdella montezumaand its pelagic amphipod prey(Hyalella montezuma)were monitored for 1 year in Montezuma Well, Arizona, U.S.A. High densities ofH. montezumaoccurred in the subsurface strata of the water column during the day, but a substantial portion of the population migrated into the surface 1 m at sunset.E. montezumaremained in the lower water strata during the day, but migrated vertically after sunset to exploit the high densities ofH. montezumanear the surface. Densities ofE. montezumaprogressively increased in the upper strata of the water column after sunset as light energy fell below 1 μEin m−2s−1. It is suggested that the synchronized nocturnal migrations of the predatorE. montezumain relation to its preyH. montezuma, increases the foraging efficiency of the leech in the highly predictable environment of Montezuma Well.
Growth and maturation of a North American fairy shrimp, Streptocephalus seali (Crustacea; Anostraca): a laboratory study
Authors: ANDERSON GARY , HSU SHEAU‐YU 
Published: May 2006

SUMMARY.

We evaluated survival, growth and time to maturation of the fairy shrimp, Streptocephalus seali Ryder, in the laboratory at various combinations of temperature and water hardness.
Both independent factors affected survival and growth of S. seali. Multiple regression analysis and response surface modelling predict that after 4 days, over 80% survival is obtained at temperatures from 14 to 28°C and water hardnesses from 60 to 130 mg CaCO3 1‐−1.
Growth rates of larvae were often maximum at physicochemical conditions other than those which had promoted maximum rates of survival. For example, after 12 days mean total body length was almost 12 mm in larvae which had been maintained at 34°C (80 mg CaCO3 1‐−1): the maximum survival rate had been obtained at 19°C. Total length was directly correlated with temperature at the lowest hardness tested, but not at the other two hardnesses (100 and 120 mg CaCO3 1‐−1). At the latter water hardnesses, total length was significantly less at 34°C than at 32°C on all three sampling occasions (4, 8 and 12 days post‐hatch).
Similarly, developmental stage of larvae correlated well with temperature but larvae reared at 34°C did not develop more quickly than those reared at 32°C. After 12 days, most larvae at the two highest temperature treatments had developed at least to Stage 14 and many were nearly mature; at 17°C most larvae were still at Stage 10.
During our study of maturation rate of females we noted that egg production was initiated after completion of fourteen or fifteen moults. Mean time to maturation at 27°C (17.3±2.8 days) exceeded that at 32°C (12.3±2.6days). The minimum time to maturation of a shrimp was 9 days at 32°C.
Chironomid biomass determination from larval shape
Authors: NOLTE ULRIKE 
Published: May 2006

SUMMARY.

Ash‐free dry weights and dry weights of each larval instar were determined for nine chironomid taxa using unpreserved material. Larval weight (wμg) was related to body length measurements (l mm) by the equation In w= In a+b In l.
For a given taxon. the constants In a and b were dependent on larval size and shape, respectively: b was found to increase with larval length, while taxa with characteristically stout larvae yielded higher values for In a.
Comparison of measurements of freshly‐killed chironomid larvae with measurements taken after preservation in 70% ethanol showed no change in body shape due to preservation. Length measurements from larvae preserved in this way are therefore suitable for use in the calculation of larval biomass when the relationship to the unpreserved weight is known.
Maximum larval lengths and mean body proportions (length: width ratios) are reported for thirty‐two chironomid taxa.
Macroinvertebrate distribution and production on the floodplains of two lowland headwater streams
Authors: GLADDEN JAMES E. , SMOCK LEONARD A. 
Published: May 2006

SUMMARY.

Spatial and temporal distribution, abundance and production of the floodplain macroinvertebrate communities of two low‐gradient headwater streams in Virginia, U.S.A., were studied over 1 year.
Spatial and temporal distribution patterns of invertebrates were affected by inundation patterns. Numbers, biomass and production were higher in low than high floodplain areas and on a floodplain continuously inundated over 9 months compared with a floodplain completely flooded only occasionally during storms.
The predominant species in terms of numbers and production on both floodplains was the harpacticoid copepod Attheyella illinoisensis Forbes. Other species with relatively high production were the sphaeriid clam Pisidium sp., the leptophlebiid mayfly Leptophlebia sp., the isopod Caecidotea racovitzai (Williams), and the chironomids Paratendipes sp. and Polypedilum spp.
Annual invertebrate production (dry weight) on the floodplain continuously inundated over 9 months was 6.1 g m−2; production on the periodically inundated floodplain was 1.7 g m−2. Collector‐gatherers accounted for 58–61%, and predators 19–25%, of the production.
Annual invertebrate production on the floodplains, calculated on the basis of a linear metre of channel length, was 84–490 gm−1, or about one to two orders of magnitude greater than probable production in the channels, suggesting the significance of floodplain invertebrates to stream system trophic dynamics.
Zooplankton in Rainbow Bay, a Carolina bay pond: population dynamics in a temporary habitat
Authors: TAYLOR BARBARA E. , MAHONEY DIANE L. 
Published: May 2006

SUMMARY.

Rainbow Bay is a temporary freshwater pond in South Carolina, U.S.A., that typically fills in winter and dries in spring or summer. We studied population dynamics of zooplankton in 1984 and 1985 when it held water for 282 and 57 days, respectively. The zooplankton were diverse, including one species of calanoid copepod, nine or more cyclopoid copepods, nineteen or more cladocerans, and twelve or more rotifers. The community was initially dominated by the copepods Diaptomus stagnalis and Acanthocyclops vernalis or Diacyclops haueri, later by cyclopoids and cladocerans including Daphnia laevis and Simocephalus spp.
Laboratory experiments with sediments from the dry pond support the inference from field data that time of emergence from resting stages was a proximate cause of the initial succession of species. The experiments also showed that eggs of the calanoid copepod, Diaptomus stagnalis, were inhibited from hatching in early November, but became ready to hatch by late November. A similar inhibition was not observed for cladocerans or cyclopoid copepods.
Food limitation appeared to influence population dynamics following emergence. For the cladocerans Daphnia laevis and Simocephalus spp., great reductions in size‐specific fecundity occurred 1 month (1985) or 3 months (1984) after the pond filled and were associated with disappearance of the rotifer Conochilus hippocrepis. The cladocerans produced ephippia when their fecundities declined. Reproduction of Diaptomus occurred before cladoceran fecundities decreased in 1984, but during their decline in 1985. Broods of Diaptomus were smaller in 1985.
The impact of invertebrate predators was probably greater than that of vertebrate predators, but neither was sufficient to prevent over‐exploitation of food resources. Prey consumption rates by salamander larvae were estimated from diets and population densities of the larvae in 1984 (Taylor et al., 1988). Their impact on the zooplankton was low in February, increased in March and April as the larvae grew, and then
Measurement of lift and drag forces in the m N range experienced by benthic arthropods at flow velocities below 1.2 m s−1
Authors: WEISSENBERGER J. , SPATZ H.‐Ch , EMANNS A. , SCHWOERBEL J. 
Published: May 2006

SUMMARY.
1. A flow tank was constructed which generates homogeneous and stable flow of water up lo velocities of 1.2 m s−1.2 A sensitive, two‐component balance with its platform inserted in the bottom of the flume allowed the measurement of drag and lift forces in the mN range.3 The drag forces experienced by several benthic arthropods, which cling to the roughened surface of the platform, are proportional to the square of the flow velocity.4 Large biological variations in lift forces, leading even to negative lifts in some cases, are indications of special adaptations of the animals to counter the danger of being swept away from their support.
The importance of acid episodes in determining faunal distributions in Welsh streams
Authors: WEATHERLEY N. S. , ORMEROD S. J. 
Published: May 2006

SUMMARY.
1. In regional studies of surface‐water acidification, annual means of chemical variables are often used to describe differences and change. Outputs from hydrochemical models are often in the form of mean values, which are used in biological models, and these, in turn, are usually derived from responses to mean conditions. Thus, biological forecasts are constrained to ignore the possible effects of the short‐term variations in water chemistry which characterize acid streams. This approach requires appraisal.2. Here, regional Welsh data and daily records from a smaller number of streams were used to investigate the estimation of pH parameters. Variations in aluminium concentration in relation to pH were also assessed. Empirical relationships between invertebrate assemblages, fish populations, mean stream chemistry and measures of fluctuation in pH and aluminium concentration were explored.3. In general, pH or Al variability and mean pH or Al in Welsh streams were closely related, so that the biological influences of episodes could not easily be separated from those of chronic conditions. Mean pH and mean aluminium concentration were the most effective pH and aluminium statistics used in multivariate models of trout density, which were not improved by including other pH or aluminium variables. For models of invertebrate assemblages based on mean pH or mean aluminium, the inclusion of variables related to episodicity (e.g. pH minimum, aluminium maximum) gave moderate increases in precision.4. This analysis indicates that it is reasonable to use means of stream chemical variables in biological models of acidification. Consideration of chemical variability could give improvements in some cases, but at the expense of increased model complexity and effort in parameter selection. Nevertheless, we emphasize the need for accurate calibration of both biological and hydrochemical models.
The effect of aquatic plant chemistry and morphology on feeding selectivity by the crayfish, Orconectes virilis
Authors: CHAMBERS PATRICIA A. , HANSON JOHN M. , PREPAS ELLIE E. 
Published: May 2006

SUMMARY.
1. Feeding preference trials conducted with male and female crayfish (Orconectes virilis) showed that out of ten submersed aquatic plant species, Chara sp. and Lemna trisulca were the preferred food sources, followed by Myriophyllum exalbescens or Utricularia vulgaris.2. Analysis of plant fibre, alkaloid, total phosphorus, total and available nitrogen, and organic content showed that crayfish feeding preferences were not related (P>0.5) to plant fibre or alkaloid content but were negatively correlated (P<0.05) with plant nutrient content such that species of low nutritional value (Chara and Lemna) were consistently preferred.3. Despite this preference for low nutrient food, daily intake rates by crayfish for phosphorus, nitrogen and organic matter were greatest when feeding on Lemna or Chara due to the large quantity consumed.4. We suggest that feeding preferences of O. virilis are not determined by plant chemistry but, rather, relate to ease of handling small, short, bottom‐dwelling plants such as Chara and Lemna as compared with large erect, roseate or floating‐leaved forms. Because crayfish are selective herbivores, their introduction into waters where they do not naturally occur could have a dramatic effect on both the species composition and biomass of submersed plants.
Characterizing individual, population and community effects of sublethal levels of aquatic toxicants: an experimental case study using Daphnia
Authors: JONES MATTHEW , FOLT CAROL , GUARDA SONIA 
Published: May 2006

SUMMARY.
1. The relationship between toxicant‐induced changes in the feeding behaviour of the cladoceran, Daphnia catawba (Coker), and subsequent effects at population and community levels were experimentally addressed.2. We adapted a method for measuring the thoracic appendage beat rate of individuals (termed the TAR and positively correlated with daphnid feeding rate) after exposure to toxicant at known levels, for use as a behavioural bioassay for low levels of aquatic toxicants. The TAR declined significantly with an increase in both sublethal and lethal levels of the surfactant, sodium dodecyl sulphate (SDS).3. We also measured population level effects (i.e. rates of reproduction, survival, and R0), and found that reductions in these values occurred at the same concentrations as the effects on individual behaviour.4. In most cases, the changes in feeding behaviour occurred more rapidly (≤30h) than changes in population parameters (days to weeks).5. We conclude that toxicant‐induced changes in individual feeding behaviour can provide a quicker estimate of effects on individuals and of potential community effects (i.e. effects on their prey populations) than measurements of population parameters. In addition, due to its sensitivity at low levels of toxicants, the behavioural bioassay may be particularly helpful in identifying effects of sublethal levels of aquatic pollutants.
Other environmental factors affect the size of crests developed by Daphnia carinata (Cladocera: Daphniidae) in response to notonectid predators
Authors: BENZIE JOHN A.H. 
Published: May 2006

SUMMARY.
1. Crest size and body size was measured in Daphnia carinata King sampled from field enclosures in which environmental conditions and notonectid predator (Anisops Hyperion Kirkaldy) levels had been manipulated, and from control treatments which had predator levels and other environmental factors equivalent to those in the natural environment.2. Individuals of D. carinata developed larger crests in treatments with predators than in treatments without predators.3. The environmentally manipulated treatment was considered to have lower levels of food but was also likely to have undergone other changes in physicochemistry and resource variability that may have affected crest size. The effect of the manipulation cannot be confirmed, therefore, as the result of variation in food levels. Animals in the treatments considered to have lower amounts of food had smaller crests than in the control treatment irrespective of whether predators were present. The effects of environmental manipulation and predators were additive.4. Enclosures without predators, but in which water from the natural, predator‐rich, environment was exchanged through the enclosure walls, showed no evidence of a chemical induction effect. Chemical induction effects may have been countered by a reduced food supply resulting from the higher D. carinata population densities that developed in these enclosures.5. This work provides a second example of an alteration of the morphological response of daphnid prey to predators by environmental factors, probably food, and suggests this phenomenon may be general in cladoceran species displaying predator‐induced changes in morphology.
The growth of brown trout (Salmo trutta) in mild winters and summer droughts in upland Wales
Authors: WEATHERLEY N.S. , CAMPBELL‐LENDRUM E.W. , ORMEROD S.J. 
Published: May 2006

SUMMARY.
1. We compared the observed annual growth of 0‐ and I‐group trout in nine Welsh upland streams, with growth predicted from temperature assuming that this was the only limiting factor.2. Autumn weights of second year fish were 51–67% of predicted (Gmax) values in 1988, but only 30–40% in 1989 and 1990 when drought occurred. Though initial weights of fry were unknown, simulations suggested that first year growth was also less than Gmax, but with no obvious effect of drought.3. To evaluate the possible effects of future climate change, we simulated stream temperature regimes 1.5–4.5°C above those of a recent year with temperatures similar to the long‐term average. Growth was set at 60%Gmax for both 0‐ and I‐group, or at 40% for I‐group to represent the effect of drought. As winter temperature increased, time to hatching and emergence decreased, for example by 56 and 49 days respectively for a rise of 3°C. 0‐group growth was slightly enhanced at up to + 3°C but retarded at + 4.5°C. Simulations of I‐group growth suggested that warmer winters could enhance trout growth while warmer summers would only increase growth if there were no adverse effects of drought.4. We discuss many uncertainties in these simulations, which nevertheless suggest the magnitude of possible effects of climate change.
Effects of phosphorus limitation on the epidemiology of a chytrid phytoplankton parasite
Authors: BRUNING KEES 
Published: May 2006

SUMMARY 1. The effect of phosphorus limitation of the diatom Asterionella formosa Hass. on growth, survival and epidemic development of its fungal parasite Rhizophydium planktonicum Canter emend. was estimated, using measurements of production and infectivity of the zoospores of the chytrid grown on host cultures with different phosphorus‐limited growth rates.2. Phosphorus‐limited host cells were less susceptible to infection with zoospores of the parasite than non‐limited host cells.3. The sporangia on phosphorus‐limited algae produced substantially less zoospores, but the development time of these sporangia was only slightly reduced.4. As a result of these effects, Rhizophydium will reach lower growth rates at a given host density, and survival of the parasite will require higher host densities when Asterionella is phosphorus‐limited.5. The zoospore production remained high enough to enable the parasite to grow faster than the alga at sufficiently high host densities, both at limiting and non‐limiting phosphorus levels.6. In spite of the reduced growth rate of the parasite, phosphorus limitation of Asterionella was found to facilitate the development of a Rhizophydium epidemic. This was a consequence of the reduced algal growth rate at phosphorus limitation, which makes the host population more easily outgrown by the parasite.7. Phosphorus limitation of the host could reduce the threshold host density required for the development of an epidemic by a factor of 2.5.