摘要:

SUMMARY1 The potential importance of interactions between macro‐ and meiobenthos in the littoral zone of takes was studied in a series of laboratory experiments with a chironomid and a chydorid.2 In a situation of intraspecific density dependence,Chydorus pigerSars inhibited the growth ofChironomus ripariusMeigen, while both second‐ and fourth‐instar C,ripariusstimulated the parthenogenetic reproduction of C.piger.3 The meiofaunal chydorids may thus have a structuring effect on macrofaunal chironomid populations by interfering with the early‐instar larvae.4 With macro‐ and meiofaunal species both operating at the primary consumer‐level of the food web, this kind of complex interaction will affect the magnitude of secondary production available to hi

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00738.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 The magnitude and range of water flow rates were measured within and adjacent to plant beds at different depths and among different dominant submersed plant species in the littoral zones of two lakes with contrasting morphometry.2 There was very little variability in within‐bed flow rates, either for locations within or among beds. However, when significant differences occurred in within‐bed flow rates, the higher rates occurred predominately near the bottom of theScirpus subterminalisbed where the plant surface area to water volume ratio was lowest.3 Factors such as bed depth and dominant species had little effect on within‐bed flow rate variance. Flows external to the plant beds were dissipated within 10–15 cm of the outer plant‐bed boundary even under severe external flow‐rate conditions (flow rate ∼ 30cms−1).4 The mean within‐bed flow rate was 0.07cms−1and individual experiment means ranged from 0.03 to 0.46cms−1. These flow rates resulted in estimates of laminar flow boundary layer thickness, 1 mm from the leading edge of the leaf, ranging from 9.1 to 2.3mm. These estimates are much larger than submersed macrophyte leaf t

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00739.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 Laboratory experiments compared the susceptibilities of six ciliates and the rotiferKeratella cochlearisto predation and interference fromDaphnia pulexandBosmina longirostris.2 Susceptibilities of the ciliates toD. pulexwere similar to or less than that of the rotifer, and decreased with increasing ciliate size. Most ciliates were just as susceptible toB. longirostrisas to the much largerD. pulex. The jumping response of the oligotrichStrobilidium gyransappeared to be an effective defence againstB. longirostris.3 Clearance rates ofB. longirostrisandD. pulexon different ciliate species at a density of 1,3 ciliates ml−1ranged from 1–30 to 5–24ml ind.−1day−1, respectively. In natural plankton communities, cladocerans could impose high mortality rates on ciliates and shift the size structure of ciliate assemblages towards larger and less susc

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00740.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 The kinetics of surface phosphatase activity (PA) in the diatomSynedra acuswere studied at low substrate concentrations that are frequently encountered in freshwaters and pH variations typical of hardwaters, ranging from pH 7 to pH 9. Higher pH resulted in higher values for the half saturation constant (Km) and the maximal velocity (Vmax).2 The pH optimum of PA was shown to be a linear function of the logarithm of substrate concentration.3 Similar slopes of Michaelis‐Menten curves at different pHs in the range of low substrate concentrations indicate that the species is well adapted to hardwaters. The rate of release of phosphate from enzymaticaliy hydrolysable phosphorus was calculated from Michaelis‐Menten kinetics for lake‐water samples dominated byS. acus. Algal surface phosphatases were responsible for the hydrolysis of 1.54–1.64 nmmin−1although incubation was performed at a lake temperatur

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00741.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 We used biovolume as a simple non‐destructive means for estimating biomass for several tubificid and chironomid species. Biovolumes were determined by treating the organisms as cylinders and measuring body lengths and diameters; estimates were verified by measuring the displacement of water by live organisms in a 5‐ml burette. In addition, factors were determined for the conversion of biovolume (V) into wet weight (WW), dry weight (DW) and ash‐free dry weight (AFDW).2 For six tubificid species, regression functions between the diameter of segment XI (D11) and the biovolume enabled the prediction of any biovolume merely by measuringD11. This method, however, underestimated biovolumes ofBranchiura sowerbyiby 38–47% compared with burette measurements. This difference is largely attributable to the mountant we used during identification.3 For ten chironomid species a linear relation was found between body length and the diameter of abdominal segment 5. The biovolume ofChironomus muratensiswas underestimated by an average of 12% compared with burette measurements.4 Specific gravity (WW:V) amounted to 1.07 and 1.05, DW:WW ratios were 0.20 and 0.142 and AFDW:WW ratios were 0.182 and 0.129 for Oligochaeta and Chironomidae, respectively.5 The biovolume method is not yet very accurate for Oligochaeta, but to our knowledge, it is the only practical method that can be used in natural polyspecific communities that need to be treated with elucidating media for identification. For those Chironomidae that need no elucidation for identification, this method is time saving and just as accurate as the direct body sha

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00742.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 Two experimental approaches were used to examine the predation risk of six littoral cladoceran and ostracod species to two size classes of the damselflyLestessp. Behavioural observations were conducted in a 2–1 arena and predation rate experiments in 1–1 jars in the laboratory.2 Behavioural observations revealed that attack and capture efficiencies byLesteswere higher on smaller cladocerans (PolyphemusandCeriodaphnia) than on other taxa. SmallLesteshad little success ingesting the small ostracodCypridopsis, whereas largerLestescaptured and ate it easily.3 Predation‐rate experiments showed thatLesteshas a clear preference for smaller cladocerans over both a large cladoceran(Simocephatus)and all three ostracods (Cypricercus, Cyclocypris, andCypridopsis). MostLesteswere unable to consume the largerCypricercus.4 Attack rates and predation rates were highly variable among individual predators.5 These data indicate that damselfly larvae are size selective and consume all but very large cladocerans more readily

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00743.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 The effects of a forest disturbance were investigated by comparing production of leaf‐shredding aquatic insects in three streams draining a mature hardwood forest and three streams draining an 11‐year‐old, cable‐logged clearcut.2 Reference streams contained significantly greater mean annual standing crop of leaf material and significantly more slow‐processing leaf material than disturbed streams. Disturbed streams had a significantly higher mean annual standing crop of fast‐processing leaf material than the reference streams.3 Leaf‐shredding cranefly (Tipula abdominalis), caddisfly (Pycnopsyche gentilis), and stonefly (Tallaperla maria) larvae comprised over 95% of shredder biomass in all streams. Total shredder production was significantly greater (P<0.05) in disturbed versus reference streams, but individual production rates were not significantly different between stream types.4 Pycnopsyche gentilislarvae were present at higher densities and achieved significantly greater annual biomass in disturbed versus references streams, Biomass ofP. gentiliswas significantly correlated with the standing crop of fast‐processing, early successional leaf material in samples, whereas biomass of other shredders was correlated significantly with medium or slow‐processing leaf species characteristic of later st

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00744.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 A dense population of a large (over 6.5mm long), semiaquatic, predatory nematodeAnatonchus dolichuruswas found in the delta of the River Dokka, Norway. This is the first time it has been reported in surface fresh waters.2 Nematode distribution was related to water depth, with maximum abundance (over 24000 ind.m−2) occurring in shallow areas (0.5–2.0m). Sediments at all stations with a high density ofA. dolichuruswere dry and exposed to air and ice during winter and early spring, and overgrown with macrophytes during summer.3 This predator contributed a greater fraction of total numbers and biomass of the nematode fauna than predatory forms in other known freshwater nematode assemblages. It constituted up to 15.6% of numbers and up to 90% of total nematode biomass.4 Anatonchus dolichuruspreyed on Nematoda, small Oligochaeta (mainly Enchyrraeidae) and Chironomidae. It was able to reduce the density of these meiofaunal taxa when present in large numbers in experim

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00745.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 Biofilms, the accumulation of micro‐organisms, exoenzymes, and detritus particles on submerged surfaces, may change the quality of leaves and wood as sources of food and/or habitat for invertebrates. We examined the relationship between macroinvertebrate assemblages and biofilm development on leaves and wood in a boreal river.2 Arrays of white birch ice‐cream sticks and sugar maple leaves were placed at fast‐ and slow‐current sites. Samples were collected periodically, and assayed for microbial biomass (ATP, ergosterol, chlorophylla) and macroinvertebrate colonizers.3 Microbial biomass and macroinvertebrate density were consistently greater on wood than leaves. Taxon richness was similar for all substratum/current combinations, but taxon density (number of taxa m−2) was greater on wood. Macroinvertebrate density and taxon richness correlated with all microbial indicators when data from both substrata were pooled.4 Leaves did not support as great a density of invertebrates as wood perhaps because of their faster breakdown rate and truncated biofilm development. Greater stability and the potential for surface complexity may make wood a site of higher macroinvertebrate dive

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00746.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SUMMARY1 Experiments were designed to determine the relative importance of chemical and visual stimuli in eliciting predator avoidance behaviour in juvenile freshwater crayfishPacifastacus leniusculus(Dana).2 Crayfish placed in visual and/or chemical contact with one of two predators exhibited marked avoidance behaviour, spending less time walking and climbing and more time within shelters.3 The combined effects of both visual and chemical stimuli increased crayfish shelter use and reduced walking and climbing activity to a greater degree than either stimulus when presented alone.4 Crayfish exhibited avoidance behaviour in response to chemical stimuli during periods of light and darkness. Visual detection of predators elicited avoidance behaviour during the day.5 It is suggested that the behavioural response of P.leniusculusto chemical stimuli reduces the likelihood of being detected by visual predators, and that chemical stimuli lower the response threshold for avoidance behaviour in crayfish reacting to visual stimuli. The adaptiviry of using chemical cues to detect predators is e

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1993.tb00747.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY