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  • 1
    Electronic Resource
    Electronic Resource
    Comparative and Experimental Approaches to the Study of Microbial Food Webs (1991)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 38 (1991), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The study of microbial food webs is dominated by field measurements of microbial standing stocks and rate processes and to a lesser extent by laboratory studies. These approaches reflect the concerns of microbial ecologists to assess accurately the capabilities of microorganisms and to compare microbial processes to other ecosystem parameters. These approaches have led to enormous advances in understanding microbial food webs. Reconciling our expanding knowledge with general questions about the significance and representation of microbial food webs in ecosystem studies requires additional approaches including comparative studies and field experiments. Comparative studies, analyses of microbial stocks or rates across a wide range of ecosystems, lead to quantitative models of microbial processes. These models facilitate testing of hypotheses at a very general level, allow the comparison of different stocks or rate processes across a gradient of systems, and detect unusual situations or outlier systems. Field experimental manipulations offer the advantages of working with intact natural communities, of direct evaluation of results with statistical methods, and of testing important qualitative hypotheses. Both comparative and field manipulation studies have led to important advances in the study of microbial food webs and should be expanded.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.1991.tb04807.x
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  • 2
    Electronic Resource
    Electronic Resource
    Biological Control of Eutrophication in Lakes (1995)
    s.l. : American Chemical Society
    Environmental science & technology 29 (1995), S. 784-786 
    Details
    ISSN: 1520-5851
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/es00003a028
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of an invasive bivalve on the zooplankton community of the Hudson River (1998)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 39 (1998), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Previous studies documented that zebra mussels became abundant in the Hudson River during 1992 causing an 80–90% reduction in phytoplankton biomass. This study used intervention time series analysis of abundance, biomass and reproduction over the period 1987–95 to assess changes in zooplankton in response to the invasion.2. Zebra mussels caused a size-dependent decline in zooplankton. Microzooplankton, including tintinnid ciliates, rotifers and copepod nauplii all declined in 1992 and were scarce thereafter. Mean abundances of post-naupliar copepods and of cladocerans were also lower following the invasion but these changes were not statistically significant (P 〉 0.05). Egg ratios and clutch sizes for the dominant cladoceran, Bosmina freyi, were not significantly related to zebra mussels, even though relatively low egg ratios were observed after the invasion.3. The strong declines in microzooplankton were probably caused by direct zebra mussel predation. Estimated consumption rates by mussels were roughly equivalent to maximum microzooplankton growth rates.4. The total biomass of zooplankton in the Hudson River declined by more than 70% following the invasion. Annual average zooplankton biomass was correlated with chlorophyll, but biomass per unit chlorophyll in the Hudson River was much lower than in lakes. The present study hypothesizes that this lower biomass reflects limitations by riverine flow and by predation during summer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.1998.00266.x
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  • 4
    Electronic Resource
    Electronic Resource
    Ciliate protozoans as links in freshwater planktonic food chains (1979)
    [s.l.] : Nature Publishing Group
    Nature 277 (1979), S. 563-565 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Ciliate protozoa ingest bacteria in nature12 and grow on them as a sole food source in the laboratory13. Furthermore, field studies indicate that planktonic ciliates are actively preyed on in nature. Manipulations of crustacean zooplankton densities in enclosures of lake water14 reveal that ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/277563a0
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  • 5
    Electronic Resource
    Electronic Resource
    Ecosystem size determines food-chain length in lakes (2000)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 405 (2000), S. 1047-1049 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Food-chain length is an important characteristic of ecological communities: it influences community structure, ecosystem functions and contaminant concentrations in top predators. Since Elton first noted that food-chain length was variable among natural systems, ecologists have considered ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35016565
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  • 6
    Electronic Resource
    Electronic Resource
    Life history variation within a parthenogenetic population of Daphnia parvula (Crustacea: Cladocera) (1984)
    Springer
    Oecologia 63 (1984), S. 43-51 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Evidence for genetically determined life history variability within a population or a species is rare. In this three year experimental examination of a parthenogenetically reproducing population of the planktonic crustacean Daphnia parvula, we found evidence for a succession of clones or groups of clones that exhibited distinctive body size and reproductive differences that were maintained after numerous generations under standardized conditions in the laboratory. The D. parvula population reached maximum density in the fall and maintained relatively high densities through the winter and spring. Isolates from this fall-winter-spring period all had a larger body size at death and higher fecundity when compared with summer isolates under natural food and temperature conditions. These differences could not be accounted for by differences in temperature and food abundance among the seasons. An additional difference in these experiments was a shift in reproductive effort by the summer isolate which produced a higher proportion of its offspring in the first two broods. The shift in life history characteristics and a summer decline of the Daphnia parvula population was correlated with both an increase in inedible and perhaps toxic blue-green algae and an increase in a dipteran predator Chaoborus. Comparison of the survivorship curves for all of the seasonal life history experiments indicated that D. parvula survivorship was not lower during the summer discounting a toxic effect from blue-green algae. Positive population growth on natural food in the laboratory at this time indicated food was not limiting and that predation was the probable cause of the population decline. Laboratory life history experiments under standardized food and temperature conditions were run with D. parvula isolates from the spring and summer plankton. Genetically based differences as determined in these experiments were smaller body size, lower fecundity, smaller brood size, and shorter life span for the summer animals relative to spring animals. Thirty seven percent of the summer animals also reproduced at an earlier age under standardized conditions. The shift in reproductive effort to earlier broods by summer animals rnder natural conditions appeared to be a phenotypic response as the summer isolate did not produce a higher proportion of its offspring in early broods under standardized conditions. When estimates of predatory mortality were added to the life tables of the standardized experiments, the earlier reproduction of some of the summer animals allowed a population increase under a regime of intense predation. Life tables for the spring animals predicted a population decline under these circumstances. Predictable seasonal changes in biotic factors such as predation suggest a mechanism whereby diverse life history patterns with corresponding differences in r may be maintained within a population.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379783
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  • 7
    Electronic Resource
    Electronic Resource
    Human influence on river nitrogen (1991)
    [s.l.] : Nature Publishing Group
    Nature 350 (1991), S. 386-387 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - The overabundance of algae in coastal waters is often blamed on excessive inputs of otherwise scarce nutrients such as nitrate and other forms of nitrogen1. This nutrient overload originates primarily from rivers that discharge directly into an ocean2-3. A key question, therefore, is what ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/350386b0
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  • 8
    Electronic Resource
    Electronic Resource
    Primary production, new production and vertical flux in the eastern Pacific Ocean (1987)
    [s.l.] : Nature Publishing Group
    Nature 325 (1987), S. 803-804 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The vertical flux of POC and PON in the upper 2,000 m of the water column was measured using free floating particle traps11 at nine sites in the Pacific Ocean12'13. While traps were deployed, PP was measured at each site, using the heavy-metal-free I4C method (ref. 14). Trapped materials were ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/325803a0
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  • 9
    Electronic Resource
    Electronic Resource
    Whole-lake carbon-13 additions reveal terrestrial support of aquatic food webs (2004)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 427 (2004), S. 240-243 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Ecosystems are supported by organic carbon from two distinct sources. Endogenous carbon is produced by photosynthesis within an ecosystem by autotrophic organisms. Exogenous carbon is produced elsewhere and transported into ecosystems. Consumers may use exogenous carbon with consequent ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature02227
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  • 10
    Electronic Resource
    Electronic Resource
    Evaluating Alternative Explanations in Ecosystem Experiments (1998)
    Springer
    Ecosystems 1 (1998), S. 335-344 
    Details
    ISSN: 1435-0629
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: ABSTRACT Unreplicated ecosystem experiments can be analyzed by diverse statistical methods. Most of these methods focus on the null hypothesis that there is no response of a given ecosystem to a manipulation. We suggest that it is often more productive to compare diverse alternative explanations (models) for the observations. An example is presented using whole-lake experiments. When a single experimental lake was examined, we could not detect effects of phosphorus (P) input rate, dissolved organic carbon (DOC), and grazing on chlorophyll. When three experimental lakes with contrasting DOC and food webs were subjected to the same schedule of P input manipulations, all three impacts and their interactions were measurable. Focus on multiple alternatives has important implications for design of ecosystem experiments. If a limited number of experimental ecosystems are available, it may be more informative to manipulate each ecosystem differently to test alternatives, rather than attempt to replicate the experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100219900025
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