bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the evolution of commensalism in the Chironomidae
Authors: TOKESHI MUTSUNORI 
Published: May 2006

SUMMARY

Commensalism is widespread among the Chironomidae. Animal hosts include the Ephemeroptera, Plecoptera, Trichoptera, Megaloptera, Hemiptera, Odonata, Diptera, Mollusca and fishes. In general, benthic organisms with relatively large body size and intermediate mobility appear to be chosen most frequently as hosts.
The evolutionary advantage of a commensal mode of life in the Chironomidae is discussed. Better feeding opportunity, increased mobility, protection from disturbance and reduced predation risk are likely to constitute the four aspects of major importance in establishing commensal relations. It is proposed that the Chironomidae have always been under the pressure of both limited mobility and high predation due mainly to their morphological characteristics. Under these circumstances commensalism is considered as a convenient strategy to solve both the mobility and predation problems at the same time. In particular, association with large‐sized hosts is thought to make the chironomid commensal less vulnerable to a variety of freshwater predators which are in general gape limited.
The evolutionary path to parasitism seems to have been more difficult in the Chironomidae, with fewer taxa being recorded as parasites than commensals. The parasitic mode of life requires that the benefit of feeding directly on the host's bodily resource exceeds the cost incurred in the form of reduced fitness of the host and hence a reduced host population, the situation that a limited number of ectoparasitic chironomid species appear to tolerate.
Reproductive potential and lifetime potential fecundity of the freshwater amphipods Gammarus fossarunt and G. roeseli in Austrian streams and rivers
Authors: PÖCKL MANFRED 
Published: May 2006

SUMMARY

Fecundity of Gammarus fossarum populations at six stream sites (S1‐S6) and G. roeseli populations at two sites (S5 and S6) was studied monthly during 1985–1988, distinguishing seven morphological stages of embryonic development. Mean survival of G. fossarum eggs was 65% (60–70%) in nature and 60% (57–63%) in the laboratory; egg survival of G. roeseli was 52% (46–58%) in nature and 41% (35–47%) in the laboratory. Regressions of egg numbers per clutch against body wet weight (WWT) decreased significantly for egg developmental stages 2 to 7 (hatching).
In stream populations, ovigerous females of G. fossarum were absent in October (six sites) and November (five sites); ovigerous G. roeseli were usually absent from October until March.
Overall mean egg volume (EV) increased significantly from 0,08 ± 0.001 mm3 and 0.075 ± 0.001 mm3 for stage 2 eggs, to 0.174 ± 0.012mm3 and 0.160 ± 0.013 mm3 for stage 6 eggs of G. fossarum and G. roeseli, respectively. The dry weights of stage 2 eggs, stage 6 eggs and neonates (stage 7) were not significantly different, within and between species; mean dry weight was 36 ± 3 μg.
Egg volumes and fecundity indices (FI, weight‐specific number of eggs per clutch) were not significantly different between the same months of four successive years, so the data were pooled to give a single representative ‘year’. At most sites there were marked seasonal fluctuations in these variables. In both species, mean EV was largest for ‘winter’ eggs in December/January and smallest for ‘summer’ eggs in May, EV decreased during some months of the year when FI increased, and vice versa. Mean reproductive effort (RE = EV × FI) declined from high ‘winter’ values to low ‘summer’ values, and this difference was most marked at sites where the major foodstuff available was seasonally limited (autumn‐shed tree leaves). Overall (‘annual’) mean RE was also lowest at these sites (S3 and S4) but was some 13% greater at sites where nutrients and food were present in the greatest quantifies (S5 and S6). Specific maximum potential body sizes and hence maximum potential fecundities (fifty‐nine eggs for G. fossarum and eighty‐seven eggs for G. roeseli) were attained only at S5 and 56. Mean RE was nearly identical for G. fossarum and G. roeseli from the same sites.
At experimental temperatures (T) in the range 3.8–20.2°C, females of the same body weight carried significantly different egg numbers per clutch. The relationship between FI and T was described by a second‐order polynomial. The calculated optimum T was 12.1°C for G. fossarum and 16.3°C for G. roeseli. Interspecific differences were highly significant.
Theoretical lifetime potential fecundity was approximately 194 eggs for G. fossarum
Colonization and processing of leaf litter by macroinvertebrate shredders in streams of contrasting pH
Authors: GRIFFITH MICHAEL B. , PERRY SUE A. 
Published: May 2006

SUMMARY

Leaf litter processing rates and macroinvertebrate shredder assemblages in leaf packs were compared in four streams on the Allegheny plateau in the central Appalachian Mountains, U.S.A.; these streams were characterized by different bedrock geology and streamwater pH.
Leaf litter processing rates were fastest in the neutral streams, slowest in the acidic stream, and intermediate in the most alkaline stream.
Slower processing rates in the acidic stream were associated with lower total shredder biomass, made up predominantly by small leuctrid and nemourid stoneflies.
The differences in processing rates between the more alkaline stream and the neutral streams were not associated with differences in shredder biomass, but appeared to be related to taxonomic differences in the shredder assembiages. Insects were dominant in the neutral streams, and amphipods were dominant in the more alkaline stream.
The effects of trout on epibenthic odonate naiads in stream pools
Authors: WISEMAN S.W. , COOPER S.D. , DUDLEY T.L. 
Published: May 2006

SUMMARY

In a southern Califomian stream naiads of a lestid damselfly (Archilestes grandis Rambur) were much less abundant, moved less, exhibited fewer conspicuous behaviours, were more likely to occur in refuge areas, and had different diets in pools containing versus pools lacking rainbow trout (Oncorhynchus mykiss Richardson). To determine if trout were responsible for these patterns, we removed trout from some stream pools and added them to pools lacking trout, with unmanipulated trout and troutless pools acting as controls.
The abundance and emergence of A. grandis were drastically reduced, and the proportion of lestid populations in refuge areas greatly increased, when trout were added to pools; however, the removal of trout had less drastic effects on lestid abundance and distribution, Aeshna walkeri (Kennedy) was also more abundant in pools lacking than in pools containing trout.
Trout manipulations affected lestid behaviour, with swimming being observed only in troutless pools and movement tending to be greater in pools lacking rather than containing trout.
One week after manipulations started, the number of prey items per lestid gut was higher in troutless control than in trout addition pools. Ostracods and chironomids were more abundant, and mayflies were less abundant, in the diets of lestids from pools lacking versus containing trout. Comparisons of the environmental abundances of prey taxa and lestid diet composition indicated that lestid selectivities for Caenis were higher, and those for Paraleptophlebia, ostracods, and Eubrianax lower, in trout than in troutless pools.
Although similar at the beginning of manipulations, head widths of lestids in troutless control pools were greater than those in trout addition pools after 3 weeks.
Factors limiting the distribution of submerged waterplants in the lowland River Vecht (The Netherlands)
Authors: VERMAAT J.E. , DE BRUYNE R.J. 
Published: May 2006

SUMMARY

The significance of light climate and water movement for the absence of submerged vegetation in the largest part of the River Vecht was investigated at three stations along the river during the summer of 1991.
The underwater light climate was found to be quite adverse for the development of waterplants due to turbidity and periphyton development. Attenuation coefficients of the water were found to be high: on average 2.6, 2.8 and 3.0 m−1 for the southern, central and northern stations, respectively. In spring most of the light attenuation (90–100%) was due to the water layer; in summer periphyton and water were equally important. The light climate limited the potential occurrence of submerged macrophytes to a zone shallower than 1m. The observed distribution of the waterplants along the river's length, however, could not be explained by the light climate alone. Presence of submerged vegetation is restricted to the southern section of the river where there is relatively little boat traffic.
Wave action caused by the (mainly recreational) boat traffic was observed to negatively affect plant growth in an in situ experiment with a breakwater. This points to physical damage by wave action caused by passing boats as the main factor determining waterplant distribution. An alternative explanation is the much higher density of houseboats in the northern section. When present, houseboats effectively shade out the zone shallower than 1 m, thus preventing the development of a submerged vegetation.
Long‐term pattern of alternative stable states in two shallow eutrophic lakes
Authors: BLINDOW IRMGARD , ANDERSSON GUNNAR , HARGEBY ANDERS , JOHANSSON STEFAN 
Published: May 2006

SUMMARY

Lake Tåkern and Lake Krankesjön, two moderately eutrophic, shallow lakes in southern Sweden, have during the past few decades shifted several times between a clear‐water state with abundant submerged vegetation and a turbid state with high phytoplankton densities.
Between 1985 and 1991, Lake Takern was in a clear state, whereas Lake Krankesjon shifted from a turbid to a clear state. During this shift, the area covered by submerged macrophytes expanded, followed by an increase in water transparency, plant‐associated macroinvertebrates, and piscivorous fish. Nutrient concentrations, phytoplankton biomass and abundance of planktonic cladocerans decreased.
In both lakes, water level fluctuations were the most common factor causing shifts, affecting submerged macrophytes either through changes in light availability or through catastrophic events such as dry‐out or mechanical damage by ice movement.
Our data give further support for the existence of two alternative stable states in shallow lakes maintained by self‐stabilizing feedback mechanisms.
Hatching of Daphnia sexual eggs. I. Intraspecific differences in the hatching responses of D. magna eggs
Authors: DE MEESTER LUC , DE JAGER HILDE 
Published: May 2006

SUMMARY

To test the hypothesis that the variability in hatching response of the sexual eggs of Daphnia has a genetic component, hatching after a standardized decapsulation technique was studied in different D. magna families, resulting from intra‐ as well as interclonal crosses.
There were significant differences in hatching response between families. Average hatching rates ranged from 0.0% to 81.9%, depending on the family under study.
Offspring‐on‐parent regressions indicate that the hatching rate‐of sexual eggs is to a large extent determined by the genotype of the mother (maternal inheritance).
Our results suggest that there is ample generic variation on a microgeographic scale for characteristics related to hatching of sexual eggs in Daphnia.
A seasonal study of phosphorus deficiency in a eutrophic reservoir
Authors: NEDOMA JIŘÍ , PORCALOVA PETRA , KOMÁRKOVÁ JAROSLAVA , VYHNÁLEK VOJTĚCH 
Published: May 2006

SUMMARY

Seston elemental composition (C, N, P) and the orthophosphate uptake rate constant, k(upt), were measured in the epilimnion of the eutrophic Římov Reservoir in the period March‐August 1989.
Seasonal series of log C/P, log N/P and log [k(upt)] values were highly correlated (r2 in the range 0.84–0.93), but, based on literature‐derived criteria, k(upt) values indicated stronger P deficiency than did the C/P values.
The results showed moderate to strong phosphorus deficiency in summer, moderate deficiency at the end of the spring peak of phytoplankton, and no deficiency early in the spring or during the spring clear‐water period.
Estimating the size at maturity in field populations of Daphnia (Cladocera)
Authors: STIBOR HERWIG , LAMPERT WINFRIED 
Published: May 2006

SUMMARY

Two methods for estimating the average body size at the onset of reproduction were applied to populations of Daphnia hyalina. The first, ‘average maturation size’, assesses maturity by the relative length of abdominal processes of Daphnia; the second, ‘size at first reproduction’ (SFR), calculates the size class in which 50% of the maximum proportion of egg‐bearing females is reached.
The influence of environmental factors on the expression of the difference in length between the first and the second abdominal process was tested in the laboratory. Neither temperature nor chemical cues from predators affected the difference in length, but the processes were indistinguishable at very low food concentrations.
During one season, D. hyalina exhibited pronounced changes in fecundity, proportion of egg‐bearing adults and SFR. The pattern obtained by the two methods was similar in many cases, although maturation size estimated by the first method was slightly smaller than SFR obtained by the second method. Neither method gave reliable results during times of starvation (clear‐water phase).
Invertebrate herbivory on the submerged macrophyte Potamogeton perfoliatus in a Danish stream
Authors: JACOBSEN DEAN , SAND‐JENSEN KAJ 
Published: May 2006

SUMMARY

Invertebrate herbivory on the submerged macrophyte Potamogeton perfoliatus was studied in a Danish lowland stream during the main growth seasons of summer 1991 and 1992. Young apical leaves escaped consumption probably because of their location and dense packing, but herbivory loss increased linearly with age and exposure time of older leaves. Nitrogen content was relatively high in both young (4.61% DW) and old leaves (3.65% DW) but a food preference experiment showed that young leaves were preferred by the main herbivore, the trichopteran Anabolia nervosa.
The percentage of standing plant biomass lost to herbivory (the apparent loss) between sampling periods increased from early May to a mid‐June maximum (24.8% in 1991, 4.2% in 1992), and subsequently declined to zero within a month. The averages for the growth seasons were 10.5% in 1991 and 2.0% in 1992. Yet, the proportions of annual plant production harvested by herbivores were low and almost the same (1.3 and 1.8%) because consumption was low when plant production peaked in late summer.Consumption was almost the same early in the two years, but plant growth dynamics differed markedly and was the main factor determining apparent herbivory loss.
Despite heavy damage early in the summer, P. Perfoliatus contributed a minor fraction (1–5%) of the trichopteran diet. This fraction appeared to be restricted by the low macrophyte biomass during early summer.
The results emphasize that apparent herbivory loss does not estimate the harvested proportion of plant production, and that plant growth dynamics should be analysed to attain precise estimates of herbivory rates.
Seasonal size variation in the predatory cladoceran Bythotrephes cederstroemii in Lake Michigan
Authors: BURKHARDT STEFFEN 
Published: May 2006

SUMMARY

Dry weight, body length and spine length were measured for the exotic cladoceran Bythotrephes cederstroemii collected from offshore and inshore stations in southeastern Lake Michigan. Average dry weight of each developmental stage exhibited seasonal variation by a factor of more than 5.
Mean dry weight of Bythotrephes was closely correlated with water temperature. Contrary to the inverse relationship between water temperature and body size frequently observed for other invertebrates, the dry weight of Bythotrephes increased at higher ambient temperatures.
No significant correlation was observed between abundances of major zooplankton taxa and the dry weight of Bythotrephes. An indirect effect of temperature on prey consumption may cause seasonal variation in dry weight of Bythotrephes in Lake Michigan.
Distances between adjacent pairs of barbs, added to the caudal spine with each moult, are significantly shorter in Bythotrephes which produce resting eggs. Less material investment in the exoskeleton of sexually reproducing females was observed in favour of growth and reproduction.
A photometric technique for the measurement of plant surface area: the adsorption of Brilliant Blue dye on to plant surfaces
Authors: WATALA KATARZYNA B. , WATALA CEZARY 
Published: May 2006

SUMMARY1. A new photometric method for determining the surface area of plants, which relies on the adsorption of Coomassie Brilliant Blue G‐250 on the plant surface, is described and compared with other methods.2. The method was applied to a variety of aquatic plants and found to provide a routine procedure to determine plant surface area.
Distribution, abundance, and roles of freshwater clams (Bivalvia, Unionidae) in the freshwater tidal Hudson River
Authors: STRAYER DAVID L. , HUNTER DEAN C. , SMITH LANE C. , BORG CHRISTOPHER K. 
Published: May 2006

SUMMARY1. An extensive series of PONAR grabs was used to determine the distribution and abundance of unionid clams in the freshwater tidal Hudson River.2. The five species of unionids collected were distributed very unevenly within the river. Mean river‐wide density and biomass of unionids were 8.0m−2 and 6.2 g DM m−2 (shell‐free)., respectively.3. The environmental variables that we measured (water depth, distance from shore, sediment granulometry and organic content, presence or absence of macrophytes, and the chlorophyll a and particulate organic matter content of the water) explained little of the variation in abundance of unionids.4. The distributions of the various species of clams did not differ significantly with respect to the environmental variables measured.5. We estimate that unionids filter a significant amount of water (0.14m3 m−2 day−1, on average) in the Hudson River estuary, roughly equivalent in magnitude to downstream flushing.6. We project that unionids will serve as a major substratum for the settlement of the zebra mussel (Dreissena polymorpha), which is now invading the estuary. We emphasize that unionids may play important non‐trophic roles in large river ecosystems.
Effects of predation, trout density and discharge on habitat use by brown trout, Salmo trutta, in artificial streams
Authors: GREENBERG LARRY A. 
Published: May 2006

SUMMARY1. The effects of predation risk, fish density and discharge on habitat use by juvenile brown trout, Salmo trutta, in four artificial streams were studied. Each stream contained three habitats, riffles, runs and pools, the latter two each being further divided into shallow margins and deeper mid‐regions.2. The presence of northern pike, Esox Indus, caused trout to decrease use of pool midregions, where pike also occurred, and to increase use of other habitats. Increasing the number of trout caused trout to increase use of pools and the shallow margins of runs. Decreasing discharge reduced the area of the run and pool margins covered by water, thereby reducing use of these areas by trout.3. Habitat selection indices for the different treatments were calculated. The data indicated that riffles and the mid‐regions of runs were preferred habitats, whereas run margins and pools were inferior habitats used when intraspecific fish densities were high.4. Despite density‐ and discharge‐dependent habitat use by trout, the number of trout consumed by pike was independent of trout density and discharge.5. The results reveal the flexibility of habitat use by trout and illustrate the potential danger of applying data on habitat use in one stream to others where habitat availability and bioric interactions may differ.
Factors affecting the distribution and abundance of an unpigmented heterotrophic alga Prototheca richardsi
Authors: WONG ADELINE L.‐C. , BEEBEE TREVOR J.C. , GRIFFITHS RICHARD A. 
Published: May 2006

SUMMARY1. Numbers of the contramensal alga Prototheca richardsi were high in spring in two ponds used for breeding by anuran amphibians, but lower at other times of year and undetectable in two ponds not used by anurans. 2. Prototheca richardsi became abundant in the silt of eight experimental ponds which contained tadpoles, but remained undetectable in four otherwise identical ponds lacking tadpoles.3. Prototheca richardsi numbers in laboratory microcosms remained stable for many days in sterile tap water, but declined with a half‐life of about 6 days in pond water at 20°C.4. Further studies with microcosms using antibiotics and electron microscopy indicated that mortality of P. richardsi was caused primarily by pathogenic bacteria.
Macrophytes from lakes in the eastern Pyrenees: community composition and ordination in relation to environmental factors
Authors: GACIA ESPERANÇA , BALLESTEROS ENRIC , CAMARERO LLUIS , DELGADO OLGA , PALAU ANTONI , RIERA JOAN LLUIS , CATALAN JORDI 
Published: May 2006

SUMMARY1. Thirty‐six species of macrophytes (fourteen flowering plants, two quillworts, sixteen mosses and liverworts, and two algae) were collected in an extensive survey of 116 high mountain lakes in the eastern Pyrenees. Seventy per cent of the lakes showed macrophyte development.2. The isoetids (Isoetes lacusiris, Isoetes setaceaandSubularia aquatica) were the dominant growth form, although the natopotamidSparganium angusifoliumwas the most widespread species. Potamids (Potamogetonspp.,Ranunculusspp.), the algaNitellagr.opacaand some mosses (Warnstorfia exannulata, Sphagnum denticulatum) were often present.3. A multivariate ordination analysis (RDA‐redundancy analysis) revealed that water chemistry, altitude and vegetation cover of the catchment, and nutrient availability are major environmental factors associated with macrophyte distribution along the eastern Pyrenean lakes. Isoetids prevailed in softwater oligotrophic lakes, potamids in relatively hardwater oligotrophic lakes, andPotamogeton natansandCallitriche palustrisin small and eutrophic water bodies affected by the presence of cattle.
Particle selection over a broad size range by crustacean zooplankton
Authors: BERN LARS 
Published: May 2006

SUMMARY1. Preferences for particles over a broad size range were assessed in four crustacean zooplankton species under field conditions. The particles employed were six spherical algae with diameters of 2, 6, 13, 19, 38 and 61 μm.2. Diaphanosoma brachyurum and Daphnia cucullata preferred the two smallest particles, Chydorus sphaericus the three smallest and Eudiaptomus gracilis the 19 μm particle.3. These size preferences agree well with earlier determinations based on seston particles in the same lake, indicating consistent size preferences by these species over a broad size range.
Trophic ecology of red roach (Rutilus arcasii) in a seasonal stream; an example of detritivory as a feeding tactic
Authors: LOBÓN‐CERVIÁ JAVIER , RINCÓN PEDRO A. 
Published: May 2006

SUMMARY1. Diel feeding activity and diet of red roach (Rutilus arcasii) were determined on five occasions (February, April, June, August and November 1985) in a seasonal, fluctuating stream subject to severe summer droughts and cold winter floods.2. Except in June, the two age groups of the population (1 + and >1+) fed mainly on detritus and showed no significant differences either in their feeding intensity or in the relative contribution of the main diet components (detritus, plants and invertebrates).3. The size, abundance and availability of drifting invertebrates influenced red roach feeding. When drift was scarce or inaccessible, both age groups fed on detritus, plants, or a combination of the two. These niche shifts were a trophic tactic aimed at maintaining feeding when other, more nutritional and energetically valuable foods were scarce.4. A comparison with other populations suggested that a detritus‐based diet had no major cost in the life history of the red roach. We hypothesize that the highly opportunistic trophic strategy of this Iberian endemic cyprinid is an adaptative response to seasonal Mediterranean streams.