bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aggregation facilitates larval growth in the neotropical nymphalid butterfly Chlosyne janais
Authors: DENNO ROBERT , BENREY BETTY 
Published: November 2003

1. Larvae of Chlosyne janais (Lepidoptera: Nymphalidae) feed gregariously as early instars on the shrub Odontonema callistachyum (Acanthaceae). During the fourth instar, aggregations break up and larvae feed as solitary individuals.2. The hypothesis that aggregation increases growth rate was tested by raising larvae on intact plants in the field in different group sizes and measuring their daily growth.3. There was a striking effect of group size on larval growth whereby larvae more than doubled their weight gain by feeding in large rather than small aggregations on intact plants in the field.4. This group‐feeding advantage was lost altogether if larvae were raised on excised leaves in the laboratory, suggesting that large aggregations may facilitate growth either by inducing a nutrient sink or by overwhelming an induced allelochemical response in the plant.5. Although larval survival was higher in cages that excluded enemies than in exposed aggregations, there was no influence of group size (experimentally manipulated) on short‐term survival in the field. However, there was a weak positive relationship between short‐term survival and the size of naturally occurring larval aggregations in the field. These data provide mixed support for the notion that gregarious feeding promotes defence against natural enemies.6. Although the group defence hypothesis warrants further investigation, feeding facilitation is clearly an important factor contributing to the aggregation behaviour of C. janais larvae.
Distribution and settling of Japanese anchovy (Engraulis japonicus eggs at the spawning ground off Changjiang River in the East China Sea
Authors: ISEKI KAZUO , KIYOMOTO YOKO 
Published: November 2003

Spatial patterns in the distribution and abundance of Japanese anchovy, Engraulis japonicus, eggs were studied from net surveys in the East China Sea in May 1991. Egg abundance was> 5 × 103 eggs (100 m3)−1 in the area off Changjiang River, where a large spawning ground was developed. The vertical distribution of living eggs showed a maximum concentration at the surface (40700 eggs (100 m3)−1) and rapidly decreased to ∼5000 eggs (100 m3)−1 at 14 m. Newly spawned eggs (stage I) were found throughout the water column but were most abundant near surface. Some eggs were morphologically identified as dead owing to their abnormal development and physical damage. In contrast to living eggs, no dead eggs were found at the surface and the concentrations were low to 21 m depth (40–64 eggs (100 m3)−1). The concentration increased markedly with increasing depth, reaching a maximum of 634 eggs (100 m3)−1 near the bottom (35 m). Dead eggs accounted for less than 0.3% of the total caught within 7 m of the surface and increased exponentially to 12% near the bottom.The settling loss of dead anchovy eggs also was studied by employing sediment traps at the spawning ground. The downward flux of settling eggs was low (304–405 eggs m−2 day−1) at 15 and 20 m depths, but rapidly increased with increasing depth, reaching a maximum of 1622 eggs m−2 day−1 at 35 m (5 m above bottom). By comparing the egg flux at 20 m with the living eggs abundance in the upper 20 m, the settling loss of eggs was calculated as about 0.098 day−1. This probably represents the natural mortality of anchovy eggs caused by genetic abnormalities and incomplete fertilization.
Daily and seasonal vertical migration rhythms in Daphnia
Authors: YOUNG STEPHEN , WATT PENELOPE 
Published: November 2003

1. Clones of Daphnia longispina (O.F.M.), collected from ponds with different levels of predation, were monitored using video techniques in order to test the effects of temperature and visual cues on vertical migration behaviour.2. Endogenous rhythms were found to have a part in the control of vertical migration in some clones but responses were highly variable.3. Low temperature caused a marked increase in the amplitude of vertical migration in D. longispina, consistent with field studies.4. Clones from ponds with fish predators had larger vertical migration amplitudes than clones from ponds with no fish, providing further evidence for the genetic basis of this mechanism.
Survival of caddis larvae in relation to their case material in a group of temporary and permanent pools
Authors: ZAMORA‐MUÑOZ CARMEN , SVENSSON BO 
Published: November 2003

1. The occurrence of larvae of Limnephiluscoenosus and L. vittatus (Trichoptera) was recorded in 103 rock pools both before and after the dry periods in spring–summer (April–May and July–early August), when a great number of the pools dried out. In early spring, 84% of the pools sampled contained larvae of at least one of the species. Limnephilus coenosus larvae were present in a higher proportion of pools that later dried out than in the permanent ones, while L. vittatus larvae were predominantly found in permanent pools. Larvae of both species were found together in 31% of the inhabited pools.2. Laboratory experiments, designed to elucidate differential survival under drought conditions, demonstrated that the organic cases of L. coenosus larvae held water more efficiently than did the mineral L. vittatus cases. Full‐grown (fifth instar) L. coenosus larvae also survived dry conditions better than did L. vittatus larvae. The higher survival of L. coenosus was due to a combination of drought‐resistant case material and a higher survival ability of the larvae themselves.3. Limnephilus vittatus larvae were restricted by their low capability to withstand desiccation, although case material and food were available for L. vittatus larvae in all pools. Absence of case material and high‐quality food in many pools, however, restricted the presence of L. coenosus larvae, but this species did not suffer from heavy mortality because of desiccation and all pool populations of L. coenosus survived until pupation.4. The differences in species composition in these temporary and permanent pools can be explained by the differential site selection by ovipositing females, as well as by larval survival. The intrinsically greater survival of L. coenosus larvae during drought, together with the water‐retaining properties of the cases, allowed this species to exploit stressful and risky habitats, such as temporary pools.
The nutrient budget of a small eutrophic loch and the effectiveness of straw bales in controlling algal blooms
Authors: KELLY L.A. , SMITH S. 
Published: November 2003

1. A 1‐year intensive study of nutrient flows in Airthrey Loch, central Scotland, a small eutrophic [mean total phosphorus (TP) = 61.1 μg P l–1] well‐flushed freshwater body (area, 6.9 ha; mean depth, 1.85 m; volume, 1.274 × 105 m3; retention time, 0.44 yr), was undertaken.2. The nutrient budget was dominated by large allochthonous P inputs, equivalent to an areal load to the loch of 8.56 kg P ha–1 yr–1, which occurred predominantly during winter. In the summer, when TP inputs were low, water column levels of TP still increased, as a result of aerobic P release from sediments.3. Sorption experiments indicated potential for sediment P release at water P concentrations of up to 200 μg P l–1.4. Aerobic release rate of P from sediments to the water column of Airthrey Loch was estimated to be of the order of 1 mg P m–2 day–1, and occurred during periods of elevated water column pH.5. Straw bales placed in the loch to retard algal blooms were found not to have any demonstrable impact on algal concentrations observed during the study.
Mortality of Apatania fimbriata (Insecta: Trichoptera) during embryonic, larval and adult life stages
Authors: ENDERS GUDRUN , WAGNER RÜDIGER 
Published: November 2003

1. Egg masses, oviposition site preferences, and abiotic and biotic factors causing mortality during embryonic, larval and adult life stages of Apatania fimbriata were studied. Laboratory investigations provided information on the temperature dependence of embryonic development, measured as an increase in egg volume.2. A. fimbriata laid hemispherical egg masses, consisting of a transparent matrix containing a mean of 208 eggs. Egg masses were laid on stones situated just above the water surface in dark cavities in the stream bank.3. Two hundred egg masses were mapped and individually monitored during embryonic development. There was no significant correlation between mortality during embryonic development and any of the abiotic parameters measured. First‐instar larvae of Osmylus fulvicephalus consumed developing eggs, and chironomids preyed on newly hatched larvae.4. A mean of seventy‐two females emerged per metre of stream. Mortality during the 1993/94 life cycle was measured as a percentage of the potential number of eggs laid. Female mortality between emergence and oviposition was ≈ 80%. Eight per cent of individuals were lost during embryonic development. Larval mortality to emergence in 1994 was 11.3%. This indicates that the terrestrial life stage is probably decisive in the regulation of A. fimbriata populations.5. Duration of embryogenesis at constant temperatures (4–20 °C) in the laboratory was described best by a negative exponential function. This species is cold stenothermal and there was no hatching success at 20 °C.6. Egg volumes during embryonic development increased sigmoidally over time.
Periphyton dynamics in a floodprone prealpine river: evaluation of significant processes by modelling
Authors: UEHLINGER URS , BÜHRER HEINRICH , REICHERT PETER 
Published: November 2003

1. Periphyton chlorophyll a was measured at weekly or 2 weekly intervals from October 1992 to March 1994 at four sites in a Swiss prealpine gravel bed river that was frequently disturbed by unpredictable spates.2. To evaluate the dominant processes that control periphyton biomass, measured data were compared with a set of simulations from an empirical dynamic periphyton model. Different combinations of process hypotheses were systematically activated and deactivated in order to assess their importance.3. The simplest model leading to an acceptable agreement with measured data employs a biomass‐dependent growth rate, a detachment rate directly proportional to discharge and biomass, and a catastrophic loss rate during bed moving spates. Terms describing light or temperature dependence had a minor effect on the model fit.4. The model describes the temporal pattern of the periphyton biomass as a series of growth curves periodically truncated by spates. Within the uncertainties of the measurements, mainly caused by the spatial heterogeneity of periphyton, the biomass recovered along deterministic trajectories.5. Sensitivity analyses with respect to model parameters and model structure showed that site‐specific model parameters could not be unequivocally determined, and that the model yields similar results with slightly different formulations of processes. This indicates that the data base with respect to periphyton biomass was too small for a unique identification of model details but that the main conclusions on the significance of processes did not depend on arbitrary choices of the model formulation.
Genetic differentiation among populations of Caridinazebra (Decapoda: Atyidae) in tropical rainforest streams, northern Australia
Authors: HUGHES J.M. , BUNN S.E. , HURWOOD D.A. , CHOY S. , PEARSON R.G. 
Published: November 2003

1. Caridina zebra is a common atyid shrimp in some tropical rainforest streams in far north Queensland, Australia. Genetic variation at five allozyme loci was used to estimate the level of dispersal among populations of this species, within and between stream systems. Shrimps were sampled from nine streams in the Tully River catchment and two headwater streams in the adjacent Herbert River catchment in an area under consideration for extensive hydroelectric development.2. High levels of genetic differentiation were recorded among most populations which suggests that, like other fully aquatic species, movement is limited to a very small spatial scale.3. In the Tully catchment, populations of shrimp from streams with confluences at high altitude showed less genetic differentiation than those from streams which directly entered the lower river. Dispersal between the latter streams is clearly limited by the presence of large waterfalls and cascades.4. Adjacent stream populations were often highly differentiated, despite their close proximity, suggesting that overland dispersal is unlikely. However, populations of shrimp in the two streams in the Herbert catchment were strikingly similar in genetic structure to those in adjacent headwater streams of the Tully. Such similarity may reflect relatively recent changes in drainage patterns.
Intraspecific stoichiometric variability and the ratio of nitrogen to phosphorus resupplied by zooplankton
Authors: CARRILLO P. , RECHE I. , CRUZ‐PIZARRO L. 
Published: November 2003

1. An in situ experiment was carried out in a high‐mountain oligotrophic lake (La Caldera) to quantify the specific release rates of ammonium and phosphorus in different phases of the seasonal succession of plankton. The zooplankton community was dominated by the calanoid copepod Mixodiaptomus laciniatus.2. The rates of release of N and P (from non‐detectable to 3.58 μg N mg–1 DW h–1 and from 0.26 to 2.29 μg P mg–1 DW h–1, respectively) and the N : P released ratio (not detectable to 4.77) fell within the range typical of oligotrophic lakes dominated by copepodite assemblages.3. The values of the zooplankton N : P ratio (5 : 1 to 10 : 1 by weight) were lower than those established for other species of calanoids, and followed a well‐established pattern of seasonal variation from year to year with higher values after ice thaw and lower values as individual size increased (ontogenetic development).4. The elemental composition of the zooplankton depended on individual size, while the released N : P ratio was inversely related to the N : P ratio of the food. This pattern conforms to the predictions of the homeostasis theory of Sterner (1990).5. A feedback regulation was established between the stoichiometric composition of the zooplankton, their food and the released N : P ratio that can help explain changes in pelagic community structure during the ice‐free period.
Mesocosm experiments on the interaction of sediment influence, fish predation and aquatic plants with the structure of phytoplankton and zooplankton communities
Authors: BEKLIOGLU MERYEM , MOSS BRIAN 
Published: November 2003

1. Little Mere, U.K., received large quantities of sewage effluent until 1991, when the effluent was diverted. Experiments, carried out in mesocosms in 1992 and 1993, were designed to predict the effects of: (i) reduced external nutrient loading; (ii) reduced internal loading from the sediment; and (iii) recolonization by fish of the better aerated water. Treatments included isolation of the water from the underlying sediment or exposure to the sediment (which lacked plants in 1992, but was covered by Potamogeton berchtoldii in 1993) crossed with different population densities of Rutilus rutilus in 1992 and of Perca fluviatilis in 1993.2. Exposure to sediment (as opposed to isolation from it) resulted in no net change in the biovolumes of most major algal groups, but this masked major complementary effects on individual species. The experiments showed a decreasing influence of the sediment, between 1992 and 1993, in determining water chemistry, and an increasing pH between years but no increase in cyanophyte dominance. This had been anticipated because a lake upstream provides abundant inocula, and conditions in Little Mere after diversion of effluent were expected to favour cyanophytes.3. Roach and perch additions to the mesocosms resulted in reductions in Daphnia populations but increases in numbers of small Cladocera and copepods. Plant‐associated Cladocera were unaffected by fish. The presence of submerged plants to some extent reduced fish predation effects on Daphnia hyalina.4. The experimental results in general accurately predicted subsequent events in the open lake.
Effects of habitat structure on habitat use by Gammarus pulex in artificial streams
Authors: DAHL JONAS , GREENBERG LARRY 
Published: November 2003

1. The influence of coarse substratum and flow, coarse substratum and food, and predation risk and flow on habitat use by Gammarus pulex was studied in three experiments conducted in artificial stream channels. Each stream channel consisted of a riffle and pool habitat.2. Location of coarse substrata and food was manipulated by placing cobbles (coarse substratum) and leaf packs (food) in different habitats. Predation risk was varied by running experiments in the presence and absence of sculpins (Cottus gobio), and flow was varied by pumping water with one or two pumps.3. In all experiments Gammarus were most abundant in pools but placement of cobbles in riffles increased use of the latter. An even greater percentage of Gammarus used riffles if leaf packs were also placed there. Decreased discharge and the presence of sculpins (Cottus gobio) also caused Gammarus to increase use of riffles. These data indicate that Gammarus is able to evaluate differences in habitat quality and respond accordingly.
Embryogenesis of Dinocras cephalotes, Perla grandis and P. marginata (Plecoptera: Perlidae) in different temperature regimes
Authors: FRUTIGER ANDREAS 
Published: November 2003

1. Temperature dependence of embryogenesis of the three perlid stoneflies Dinocras cephalots, Perla grandis and P. marginata was investigated by means of incubation experiments. Special emphasis was laid on the effect of fluctuating temperatures and on intraspecific differences between populations from two different field sites in the Swiss prealps (i.e. River Necker and River Thur).2. Dinocras cephalotes embryos develop between 6.3 and 26.6 °C. The lower threshold temperature is lower than has been reported for more northern populations (i.e. from England and Norway), indicating the existence of a latitudinal gradient. Perla grandis eggs only developed between 9.9 and 18.4 °C. In P. marginata, successful embryogenesis was observed between 9.9 and 18.4 °C, but not enough eggs were available to explore the threshold temperatures.3. Embryogenesis of D. cephalotes and P. grandis was significantly faster at a 12/16 °C daily fluctuating temperature regime than at a constant 14 °C. However, no significant difference was found between the development under simulated field temperature regimes (with less distinct daily amplitudes) and constant temperatures.4. D. cephalotes, hatching of eggs from the Necker population was much less synchronous than that in the Thur population. Since the Necker discharge regime is harsher than the Thur regime, it is possible that this asynchrony spreads the risk of destruction during bed‐moving floods.
Abundance and distribution within a guild of benthic stream fishes: local processes and regional patterns
Authors: TAYLOR CHRISTOPHER 
Published: November 2003

1. Spatial patterns at regional and local scales were examined for evidence that species interactions can influence distribution and abundance within a guild of benthic fishes in upland streams of Oklahoma, U.S.A. Three groups of community patterns were examined: the species–area relationship, species–habitat associations, and interspecific associations.2. The species–area relationship for riffle habitats was compared to a null species–area model based on random placement. The observed species–area curve was steeper resulting in less species per unit area in small streams than predicted by the null model.3. Small, species‐poor streams had summed fish densities at least as high as larger, species‐rich streams, suggesting density compensation.4. Several significant patterns of negative covariation were found among species at the regional scale, before and after statistically accounting for effects due to measured habitat variables.5. For two of these negatively covarying taxa (Cottuscarolinae and Etheostomaspectabile), the influence of each species on the distribution of the other was evaluated experimentally in field enclosures varying in depth and current velocity. The sculpin C. carolinae caused a shift in habitat use by the darter E. spectabile, but no reciprocal shift was found.6. These results indicate an agreement between local and regional patterns of distribution for C. carolinae and E. spectabile and suggest that biotic interactions can influence regional patterns of distribution for species within this guild.
Intraguild predation and species exclusions in amphipods: the interaction of behaviour, physiology and environment
Authors: DICK JAIMIE , PLATVOET DIRK 
Published: November 2003

1. Data from field surveys, laboratory experiments and computer simulations of community dynamics revealed that a novel interaction among intraguild predation, physiological adaptation and environment may explain the complex distributions of two putatively competing aquatic amphipods.2. Gammarus pulex and G. tigrinus both thrive in fresh and oligohaline waters in western Europe. However, the native European G. pulex excludes the invading North American G. tigrinus from freshwaters of relatively low conductivity, whereas the reverse occurs at higher conductivities. Additionally, there is much spatio‐temporal fluctuation in the patterns of coexistence of these species.3. Laboratory experiments in The Netherlands and Ireland revealed that mutual predation of moulting individuals occurred frequently between these species. However, predation frequencies were differentially in favour of G. pulex under the ionic conditions to which this species is physiologically adapted (freshwater). On the other hand, predation was not differential under the ionic conditions to which G. tigrinus is physiologically adapted (oligohaline water).4. A mathematical model, which extends the logistic equation to include mutual intraguild predation, simulated interactions over a range of values of relevant population parameters. This indicated that G. pulex would be excluded when balanced instantaneous rates of mutual predation were combined with the known greater reproductive output of G. tigrinus. However, this reproductive advantage is overcome by any relatively small bias in the instantaneous rate of predation favouring G. pulex, leading to the exclusion of G. tigrinus. This occurs even when the reproductive advantage to G. tigrinus is relatively large. Moreover, the model generated ‘switches’ in species dominance that are determined by the relative values of reproductive rate and mutual predation. The time taken to ‘switch’ may explain the transient periods of apparent coexistence of these species observed in the field.5. The complex community dynamics of such species may thus be understood in terms of variation in the intensity of species interactions mediated by behavioural, physiological and environmental factors.