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  • 1
    Digitale Medien
    Digitale Medien
    Oxford BSL : Blackwell Science Ltd
    Freshwater biology 35 (1996), S. 0 
    ISSN: 1365-2427
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: 1. This paper describes the effects of differences in food quantity and quality on selected life history traits of Ceriodaphnia pulchella. Animals were fed with four concentrations of two green algae, Scenedesmus obliquus and Chlamydomonas globosa, given separately as well as in a 1 : 1 mixture.2. In most cases growth, reproduction and condition of the animals and consequently the rate of population increase, r, increased with food concentration. Life history parameters of animals raised on S. obliquus were lowest, whereas no significant differences were found between animals fed with C. globosa and with the mixture of the two algal species.3. In contrast to the large effects of food quantity and quality found in the laboratory, an analysis of the population dynamics of C. pulchella in Lake Tjeukemeer showed that the effect of changes in food conditions during the growing season of this species was limited, although overall food levels seemed to be poor throughout the year.4. Changes in the birth rate of the population are mainly governed by changes in temperature, and possibly by changes in the densities of the invertebrate predator Leptodora kindtii.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 48 (2003), S. 0 
    ISSN: 1365-2427
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: 1. We performed a mesocosm experiment to investigate the structuring and cascading effects of two predominant crustacean mesozooplankton groups on microbial food web components. The natural summer plankton community of a mesotrophic lake was exposed to density gradients of Daphnia and copepods. Regression analysis was used to reveal top–down impacts of mesozooplankton on protists and bacteria after days 9 and 15.2. Selective grazing by copepods caused a clear trophic cascade via ciliates to nanoplankton. Medium-sized (20–40 μm) ciliates (mainly Oligotrichida) were particularly negatively affected by copepods whereas nanociliates (mainly Prostomatida) became more abundant. Phototrophic and heterotrophic nanoflagellates increased significantly with increasing copepod biomass, which we interpret as an indirect response to reduced grazing pressure from the medium-sized ciliates.3. In Daphnia-treatments, ciliates of all size classes as well as nanoflagellates were reduced directly but the overall predation effect became most strongly visible after 15 days at higher Daphnia biomass.4. The response of bacterioplankton involved only modest changes in bacterial biomass and cell-size distribution along the zooplankton gradients. Increasing zooplankton biomass resulted either in a reduction (with Daphnia) or in an increase (with copepods) of bacterial biovolume, activity and production. Patterns of bacterial diversity, as measured by polymerase chain reaction–denaturing gradient gel electrophoresis (PCR–DGGE), showed no distinct grouping after 9 days, whereas a clear treatment-coupled similarity clustering occurred after 15 days.5. The experiment demonstrated that zooplankton-mediated predatory interactions cascade down to the bacterial level, but also revealed that changes occurred rather slowly in this summer plankton community and were most pronounced with respect to bacterial activity and composition.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 45 (2000), S. 0 
    ISSN: 1365-2427
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: 1. The effect of the addition of emulsions with different fatty acid composition to a semi-natural zooplankton community was studied in enclosures. 
2. The reactions of different taxa in the zooplankton community to the addition of the emulsions were different. The copepods showed almost no reaction, nor did the selective cladocerans (Bosmina) or rotifers (Synchaeta or Polyarthra). The non-selective filterfeeding cladocerans Daphnia and Ceriodaphnia, and the rotifer Keratella, showed responses to the addition of the emulsions. 
3. Keratella showed the highest density in the enclosures with high amounts of highly unsaturated fatty acids added, whereas both Daphnia and Ceriodaphnia reached the highest numbers in the enclosures where we added emulsions of saturated fatty acids only. 
4. Our results suggest that different taxa may be limited by different factors, even though they use similar food sources. Hence, we conclude that it is very difficult to generalize on the limiting factors in aquatic systems.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    [s.l.] : Macmillan Magazines Ltd.
    Nature 398 (1999), S. 382-382 
    ISSN: 1476-4687
    Quelle: Nature Archives 1869 - 2009
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Notizen: [Auszug] It has long been known that the waterflea Daphnia hyalina exhibits diel vertical migration in the water column, but the chemical that triggers this behaviour has not been identified. We find that trimethylamine (TMA), which is a major component of the odour produced by decaying fish, induces ...
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    Oecologia 103 (1995), S. 309-318 
    ISSN: 1432-1939
    Schlagwort(e): Coexistence ; Hybrid ; Competition ; Daphnia ; Hemispecific
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract I investigated the competitive relationships between two species of Daphnia, D. galeata and D. cucullata, and their interspecific hybrid. The term hemispecific competition was introduced to describe competition between parental species and hybrids. In eutrophic Tjeukemeer both parental species were found to compete with the hybrid, whereas competition between D. galeata and D. cucullata seemed limited. Although the effect of competition on life history traits of daphnids may be profound, the influence of the competitors on the seasonal dynamics of the Daphnia species seems limited.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    ISSN: 1573-5117
    Schlagwort(e): food web ; trophic interactions ; production ; consumption
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The interactions between the higher trophic levels in a shallow eutrophic lake were studied during the course of a year. Three fish species determined the main pathways of organic matter flow within the system: the predominantly planktivorous bream (Abramis brama), the obligate planktivorous smelt (Osmerus eperlanus), and the piscivorous pikeperch (Stizostedion lucioperca). Of the thirteen common zooplankton taxa Daphnia hyalina and cyclopoid copepods were utilized most by the planktivorous fish, while the large production of small cladocerans is almost left unutilized. The seasonal variations of production and consumption are large. This is mainly affected by seasonal variation of the water temperature. The production of O + smelt is efficiently utilized by the pikeperch. Being the most important zooplankton consumer, as well as the most important prey group, O + fish plays a key role in the Tjeukemeer food web.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Hydrobiologia 294 (1994), S. 99-103 
    ISSN: 1573-5117
    Schlagwort(e): Scenedesmus ; toxic ; culture ; Daphnia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract We cultured individuals of two Daphnia species and their hybrid on two different algae, Scenedesmus obliquus and Chlamydomonas globosa, in different concentrations. Our results suggest that culture conditions of S. obliquus can be such that the algal cells become toxic to Daphnia
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    ISSN: 1573-5117
    Schlagwort(e): microcrustacean zooplankton ; tropical limnology ; biomass ; production ; empirical relationships
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Production, biomass and productivity of the microcrustacean zooplanktonpopulations of three low-land reservoirs, Tissawewa (eutrophic), Ridiyagama(moderately eutrophic), and Muruthawela (mesotrophic) in South-east SriLanka were studied. The temporal variation of zooplankton production wasstudied in Tissawewa on basis of fortnightly sampling on five fixed samplingstations for 2 years. Zooplankton production was relatively high, mainlybecause of high copepod production predominantly realised due to twocalanoid copepods, Phyllodiaptomus annae and Heliodiaptomus viduus. Abouthalf of the copepod production was contributed by the naupliar instarstages, whereas the contribution of the eggs was generally much smaller(〈20%). In contrast, the cladoceran production consisted for ca50–70% of egg production. The results of this study werecompared with those from more than twenty other tropical and subtropicalwaterbodies reported in the literature by deriving empirical relationshipsbetween mean phytoplankton biomass and mean zooplankton biomass andproduction. Mean zooplankton biomass and annual zooplankton production werefound to be positively related to mean phytoplankton biomass, and meanphytoplankton biomass proved to be a good predictor of mean zooplanktonbiomass (r2 = 0.58) and a moderate good predictor ofannual zooplankton production (r2 = 0.43). However,the relationships between the mean phytoplankton biomass and zooplankton P/Bwere not significant neither for small-bodied and large-bodied cladoceransnor for copepods.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    ISSN: 1573-5117
    Schlagwort(e): microcrustacean zooplankton ; tropical limnology ; laboratory cultures ; growth ; development rates ; temperature
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Length growth, instar durations, fecundity and mortality rates of fivespecies of microcrustacean zooplankton from a tropical reservoir weremeasured in relation to food quantity and temperature in laboratorycultures. Three cladocerans (Ceriodaphnia cornuta, Moina micrura,Diaphanosoma excisum), one calanoid copepod (Heliodiaptomus viduus), and onecyclopoid copepod (Mesocyclops thermocyclopoides) were studied. Filteredseston (45 µm mesh) from a local pond was used for food. Two foodconcentrations were employed: (1) 10 µg chlorophyll l−1(ca 0.25 mg Cl−1), and (2) 50 µg chlorophylll−1 (ca 1.25 mg C l−1). Food levels and watertemperature (22.5, 27.5, and 32.5 °C) used, roughly covered the rangesfound in the reservoir. Although all the three growth parameters were oftenaffected to some degree by temperature and food, the quantitative responseof the species differed. Also, the species reacted differently to the threepossible interactions (i.e. food × temperature,food × instar, andtemperature × instar). This contributed to the overalldifferences in the species responses. For the cladocerans, instar durationswere always affected by temperature. The food did not affect the durationtime of the adults and that of the combined juvenile instars, the latterexcept in one case significantly. For the two copepods food level affectedthe duration times of naupliar and copepodite instars, but the effect oftemperature was only significant for H. viduus. The development timesobserved for H. viduus were extraordinary long compared with values reportedin the literature for other tropical calanoids. This suggests that foodconditions in our culture were adversely affecting its growth rates.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Hydrobiologia 360 (1997), S. 79-88 
    ISSN: 1573-5117
    Schlagwort(e): Life history ; food
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Variation in offspring size and number has beendescribed for a wide range of organisms. In this studyI investigated the relationship between resource levelof the mother and size of her offspring in thecladoceran Daphnia magna, in order to assess whetheroffspring produced at different food levels areoptimal in size for these food levels. Optimaloffspring size was defined as the size of offspringthat yields the highest parental fitness (i.e.offspring of optimal size have the highest juvenilefitness per unit maternal effort invested in them). Iobserved that especially at the higher food levels,daphnids produced offspring that are larger than thecomputed optimal offspring size at these food levels.I interpret this as a mechanism to avoid starvation ofneonates in the case of suddenly deteriorating foodconditions.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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