摘要:

SUMMARY.In an acid bog pond, the sessile rotiferPtygura beauchampiwas limited to the trap door areas of one of three distinct prey capturing organs of the carnivorous hydrophyteUtricularia vulgaris; four other co‐occurring congeneric species (U. gibba, inflatavar.minor, intermedia, andpurpurea) were not colonized. This pattern was not the result of differential capture of larvae by the prey traps. Laboratory settling experiments demonstrated thatP. beauchampilarvae select this particular substrate to the exclusion of all others. This selectivity was independent of the presence of captured prey organisms in the traps.P. beauchampilarvae select younger vestibules (trap door areas) over older ones. Observations of natural populations showed denser colonization of those slightly bigger traps closer to the plant stem. However, no relation was found between vestibular area and adult rotifer density. Selectivity for traps more proximal to the plant system was not demonstrated. In natural populations a distinct distribution of adults within the vestibule was noted. This pattern was statistically different from sites which the larvae colonize in laboratory experiments. Adult distribution is probably a modification of the larval settling pattern by site‐dependent survivorship of adults.Larval settling experiments showed that larvae select uncolonized vestibules over those previously colonized of approximately equal age. Settling outside the vestibule area was highest on traps closest to the plant stem and was related to the density of adults colonizing the vestibule.The adaptive significance of larval selection of a particular substrate is discus

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01678.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.TheChaoboruspopulation of Lake Lanao, Philippines, was sampled weekly over a 65‐week period. Specimens representing all four instars, all times of the year, and two points in the daily migration cycle were dissected for determination of gut contents.Major items in the diet of LanaoChaoborusincludeBosmina, Diaphanosoma, and the copepodid and adult stages of cyclopoid and calanoid copepods. Items that are available but seldom eaten include nauplii and rotifiers exceptKeratella. Feeding rate averages 2.5% of body weight per day in instars 3–4.Predator size affects but does not fully explain prey selection. Electivity values are much higher forBosminaandDiaphanosomathan for copepods, even though these food items overlap in size.Bosmina, which has the highest electivity value of any prey, is virtually identical in size to the calanoid nauplius, which has one of the lowest electivity values. This and other similar data suggest that prey of the same size differ greatly in palatability or vulnerability.There is a marked variation in feeding rate and food composition from day to night. The smallestChaoborusfeed more during the day than at night, but the opposite is true forChaoborusof moderate to large size. LargeChaoborusswitch from a daytime emphasis on copepod copepodids and adults to a nighttime emphasis on Cladocera.Diurnal variation between instars in food composition cannot be explained simply on the basis of the vertical distributions of predators and prey. An interaction of vertical distribution with prey density and predator selectivity does explain the overallChaoborusfeeding pattern, however. During the day, largerChaoborusmove deep into the water column where food is scarce. Their daytime feeding rate is lower due to low prey density at great depths. Low prey density is partially compensated by relaxation of preference. At night, upward migration of largeChaoborusinto an area of high prey density permits a resumption of marked selectivity and high feeding rates. SmallChaoborusdo not descend deep into the water column during the day, as their lower hunting efficiency apparently requires higher food density and use of visual cues to sustain adequate feeding rates. Prey density thus affects both the vertical distribution and feeding selectivity of theChaoboruspopulat

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01679.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.In Lake Erken there is a regular phytoplankton peak at ice‐breakup in the spring. Pechlaner (1970) studied the spring outburst of 1960. We carried out a similar study in 1973, when the climatic factors were completely different, with only 10 cm of ice and almost no snow. Thus, due to light penetration, there was a high phytoplankton biomass under the ice as early as March.Stephanodiscus astraea(Ehr.) Grun. andAsterionella formosaHass. dominated the biomass during the spring development in 1973 instead of the normally dominatingS. hantzschii v. pusillusGrun.The nutrient decrease was slower in 1973 than in 1960. A comparison of carbon assimilation and the decrease of nitrate and phosphate indicate sufficient nutrient supply in 1973. In 1960, the population grew logarithmically until the nutrients became limiting. In 1973, the average biomass was greater, but the mean probable primary production was only half that of 1960. From the activity coefficients for the 2 years it is also clear that, in 1960,S. hantzschii v. pusilluswas highly productive during its short but intensive growth period. Its minute size and high surface/volume ratio enabled it to take up nutrients rapidly and efficiently. The chlorophyll content ofS. astraeain 1973 was only half as much as that ofS. hantzschii v. pusillusin 1960. Since the light conditions under the ice in March 1973 were more unfavourable than during the exponential phase of 1960, production was much lowe

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01680.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.Feeding responses in campanulate females ofAsplanchna sieboldiwere induced with filtrates of homogenized saccate female clonemates, showing that such behaviour can be triggered entirely by chemical stimuli. The failure of campanulates to attack campanulate clonemates, however, probably cannot be explained by the tissue chemistry of these females – filtered and unfiltered homogenates of campanulates were as active as those of saccates—and appears to be a function of some property limited to the campanulate body surface.The roles of chemical and physical properties of food items in controlling feeding behaviour inAsplanchnaand other rotifers are conside

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01681.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.Daphnia magnawas maintained on two diets and exposed to acute and chronic copper stresses. Animals fed vitamin‐enriched algae were less sensitive to a chronic copper stress than animals fed a trout‐granule diet. This conclusion is based on the responses of cohorts as measured by survival, mean brood size andr, the instantaneous rate of population growth. Application factors were also significantly different for animals reared on the two foods (0.47 for algal‐fed animals, 0.12 for animals reared on trout‐granules). In contrast to chronic toxicity, 72 h LC50values were not significantly different for animals maintained on the two foods. This suggests that the mechanism of toxic action is different for acute and chronic toxicity and that, if so, the ratio between chronic and acute toxicity would not be a constant under different environmental con

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01682.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.A study of the eutrophic Lough Neagh was undertaken to ascertain the use of alkaline phosphatase activity as an indicator of phosphorus‐limited algal growth. Lough Neagh and its surrounding rivers were monitored during 1974 and 1975. Alkaline phosphatase activity increased in the lough when the algal crop increased and depleted orthophosphate to a growth‐limiting concentration. Enzyme activity was appreciable, however, at all other times of the year and may on occasions have been associated with zooplankton. The enzyme activity in the inflowing rivers was much greater than in the lough itself. Depending on enzyme stability the enzyme inputs from rivers could contribute significantly to the lough activity. Sewage disposal works effluent appeared to be a major source of enzyme activity in river water. As the alkaline phosphate activity in Lough Neagh resulted from several sources, increased activity could not be used as a reliable indicator of phosphorus limited algal gro

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01683.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.Field and laboratory studies have been carried out on the tolerance to zinc of the filamentous green algaeHormidium rivulareKütz.,H. flaccidumKütz. andH. fluitans(Gay) Heering growing in flowing waters. Forty‐seven different sites in England, France, Germany and Ireland were included, the majority of them chosen to represent examples of zinc pollution resulting from past or present mining activities. All three species were widespread both in waters free of zinc pollution and waters with zinc pollution, andH. rivulareandH. flaccidumwere frequent at a site with the highest zinc level included in the survey (mean of 22.8 mg l−1, maximum of 30.2 mg l−1Zn passing through a filter). At sites with higher zinc levels, populations showed increased resistance to zinc of the filamentous green algaeHormidium rivulareKütz.,H. flaccidumcreased resistance being largely, if not entirely, the result of genetic adaptation. An increased frequency of geniculations can occur both as an environmental and a genetic response to very high zinc levels. The application of various statistical analyses to the data suggests that two groups of chemical factors may be influencing the toxicity of zinc in the field. The first group which appears to increase the toxicity of zinc includes cadmium and lead, while the second group, which decreases the toxicity of zinc, includes magnesium, calcium and various hardness factors. As the occurrence of zinc, cadmium and lead in the field are all strongly intercorrelated, it is not possible to distinguish clearly the effects of one from the other, although the data do suggest that cadmium is more likely than lead to influence zinc toxicity. The ‘amelioration’ factors are also strongly intercorrelated in the field, so it is difficult to comment on their relative importance. There is some indication forH. rivulareat least, that an increase in PO4‐P and a decrease in pH may also reduce

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01684.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.The toxicity of zinc toHormidium rivulareKütz. in laboratory culture media is decreased by rises in the levels of magnesium, calcium and phosphate, and increased by rises in pH and cadmium. The effects of all these are sufficiently marked that they may be expected to have considerable importance in the field. In contrast, assays with sodium, chloride and sulphate showed no detectable influence of these ions on zinc toxicity.When applied at higher concentrations, calcium was always more effective than magnesium, but the reverse was sometimes true at lower concentrations. Both magnesium and phosphate were more effective in reducing zinc toxicity with zinc‐tolerant populations than with zinc‐sensitive ones. Cadmium was highly toxic, either alone or in combination with zinc; however, calcium had a proportionately greater effect in reducing cadmium toxicity than zinc toxicity. The toxic effects of zinc and cadmium were synergistic, and it seems probable that the presence of cadmium at levels of 0.01 mgl−1and above will usually lead to a significant increase in the toxicity of any zinc also present. Cadmium (in the absence of zinc) was 34 times more toxic than zinc to a zinc + cadmium sensitive population, and 15.5 times more toxic to a zinc + cadmium tolerant population. Because of the synergistic response, cadmium had an even greater effect in the presence o

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01685.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.Denitrification experiments under anaerobic and aerated conditions were carried out in the laboratory with Lake Kinneret water and with pure cultures of the denitrifying bacteriaPseudomonas aeruginosa2 Kin isolated from the lake. Although losses of nitrogen in Lake Kinneret due to denitrification have been found to occur during periods when dissolved oxygen exceeded 5 mg l−1it was found that under aerated conditions glucose as a carbon source must be added in order to get denitrification in the laboratory.Disappearance of nitrogen during the experiments was due to denitrification as shown by the nitrogen balance calculated for each sampling. The ATP content showed that no proliferation of cells took place during the experiment.The rate of denitrification was strongly influenced by and was directly proportional to nitrate concentrations. Temperature has a very slight effect on the denitrification rate. Q10for the range 15–30°C was 1.35.The role of denitrification in the nitrogen balance of Lake Kinneret is discu

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01686.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SUMMARY.A new method for collecting and handling water samples prior to their polarographic measurement is described. Its usefulness has been demonstrated by testing its ability to exclude oxygen from anoxic hypolimnetic samples. The criterion of detection was 15 μg1−1of oxygen for the 95% confidence level. Different sampling and different handling procedures were compared, and only one overall method proved to introduce no significant contaminati

ISSN:0046-5070    

DOI:10.1111/j.1365-2427.1977.tb01687.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY