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  • 1
    Electronic Resource
    Electronic Resource
    Effects of elevated CO2, nitrogen deposition, and decreased species diversity on foliar fungal plant disease (2003)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 9 (2003), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Three components of global change, elevated CO2, nitrogen addition, and decreased plant species richness (‘diversity’), increased the percent leaf area infected by fungi (pathogen load) for much to all of the plant community in one year of a factorial grassland experiment. Decreased plant diversity had the broadest effect, increasing pathogen load across the plant community. Decreased diversity increased pathogen load primarily by allowing remaining plant species to increase in abundance, facilitating spread of foliar fungal pathogens specific to each plant species. Changes in plant species composition also strongly influenced community pathogen load, with communities that lost less disease prone plant species increasing more in pathogen load. Elevated CO2 increased pathogen load of C3 grasses, perhaps by decreasing water stress, increasing leaf longevity, and increasing photosynthetic rate, all of which can promote foliar fungal disease. Decreased plant diversity further magnified the increase in C3 grass pathogen load under elevated CO2. Nitrogen addition increased pathogen load of C4 grasses by increasing foliar nitrogen concentration, which can enhance pathogen infection, growth, and reproduction. Because changes in foliar fungal pathogen load can strongly influence grassland ecosystem processes, our study suggests that increased pathogen load can be an important mechanism by which global change affects grassland ecosystems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2003.00602.x
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  • 2
    Electronic Resource
    Electronic Resource
    The effects of long-term nitrogen loading on grassland insect communities (2000)
    Springer
    Oecologia 124 (2000), S. 73-84 
    Details
    ISSN: 1432-1939
    Keywords: Key words Insect communities ; Productivity ; Diversity ; Abundance ; Nitrogen loading
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Just as long-term nitrogen loading of grasslands decreases plant species richness and increases plant biomass, we have found that nitrogen loading decreases insect species richness and increases insect abundances. We sampled 54 plots that had been maintained at various rates of nitrogen addition for 14 years. Total insect species richness and effective insect diversity, as well as herbivore and predator species richness, were significantly, negatively related to the rate of nitrogen addition. However, there was variation in trophic responses to nitrogen. Detritivore species richness increased as nitrogen addition increased, and parasitoids showed no response. Insect abundances, measured as the number of insects and insect biovolume (an estimate of biomass), were significantly, positively related to the rate of nitrogen addition, as were the abundances of herbivores and detritivores. Parasitoid abundance was negatively related to the rate of nitrogen addition. Changes in the insect community were correlated with changes in the plant community. As rates of nitrogen addition increased, plant species richness decreased, plant productivity and plant tissue nitrogen increased, and plant composition shifted from C4 to C3 grass species. Along this gradient, total insect species richness and effective insect diversity were most strongly, positively correlated with plant species richness. Insect biovolume was negatively correlated with plant species richness. Responses of individual herbivores varied along the nitrogen gradient, but numbers of 13 of the 18 most abundant herbivores were positively correlated with their host plant biomass. Although insect communities did not respond as strongly as plant communities, insect species richness, abundance, and composition were impacted by nitrogen addition. This study demonstrates that long-term nitrogen loading affects the entire food chain, simplifying both plant and insect communities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050026
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  • 3
    Electronic Resource
    Electronic Resource
    Invasions of equilibria: tests of resource competition using two species of algae (1984)
    Springer
    Oecologia 61 (1984), S. 197-200 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Single-species, steady-state chemostat cultures of two freshwater diatoms showed that Fragilaria crotonensis had a lower equilibrial requirement for silicate than did Tabellaria fenestratra. Using this information, resource competition theory predicts that Fragilaria should be able to invade silicate-limited equilibrium populations of Tabellaria, but Tabellaria should not be able to invade silicatelimited Fragilaria. This prediction was supported by a series of invasion experiments. The two species did not have detectable differences in their phosphate requirements. Invasion experiments showed that Fragilaria could invade Tabellaria cultures, but that Tabellaria could not invade Fragilaria cultures under phosphate-limited conditions. These results are consistent with predictions based on previous studies of the phosphate physiology of these genera.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396760
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  • 4
    Electronic Resource
    Electronic Resource
    Dynamics of vesicular-arbuscular mycorrhizae during old field succession (1991)
    Springer
    Oecologia 86 (1991), S. 349-358 
    Details
    ISSN: 1432-1939
    Keywords: VA-mycorrhizae ; Old field succession ; Infectivity ; Spore populations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The species composition of vesicular-arbuscular mycorrhizal (VAM) fungal communities changed during secondary succession of abandoned fields based on a field to forest chronosequence. Twenty-five VAM fungal species were identified. Seven species were clearly early successional and five species were clearly late successional. The total number of VAM fungal species did not increase with successional time, but diversity as measured by the Shannon-Wiener index tended to increase, primarily because the community became more even as a single species, Glomus aggregatum, became less dominant in the older sites. Diversity of the VAM fungal community was positively correlated with soil C and N. The density of VAM fungi, as measured by infectivity and total spore count, first increased with time since abandonment and then decreased in the late successional forest sites. Within 12 abandoned fields, VAM fungal density increased with increasing soil pH, H2O soluble soil C, and root biomass, but was inversely related to extractable soil P and percent cover of non-host plant species. The lower abundance of VAM fungi in the forest sites compared with the field sites agrees with the findings of other workers and corresponds with a shift in the dominant vegetation from herbaceous VAM hosts to woody ectomycorrhizal hosts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317600
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  • 5
    Electronic Resource
    Electronic Resource
    Predictions of species interactions from consumer-resource theory: experimental tests with grasshoppers and plants (1993)
    Springer
    Oecologia 94 (1993), S. 516-527 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We tested the ability of consumer-resource theory to predict direct and indirect interactions among species, using an experimental system of insect herbivores and herbaceous plants. Specifically, we examined interactions among three species of grasshoppers (Melanoplus femur-rubrum, Spharagemon collare, andPhoetaliotes nebrascensis; Orthoptera, Acrididae) and herbaceous plants in experimental field cages placed over existing fertilized or unfertilized vegetation in a Minnesota old field. For the conditions inside these cages, we addressed whether (1) grasshopper diet predicted the presence of competition among grasshopper species, and (2) direct effects of grasshoppers on plants produced indirect interactions among plants, grasshoppers and soil nitrogen. Overall,M. femur-rubrum ate a greater proportion of forbs in cages, while the other two species ate primarily grasses. As expected, a pair of grasshopper species competed if they had similar diets. However, there were important exceptions that could be explained from observed indirect effects, although alternative explanations were also possible. First, all three grasshopper species significantly shifted their diets in the presence of other species, and these shifts occurred most often when competition was expected or occurred. Second, the two grassfeeding species reduced the biomass of the dominant grass (Schizachyrium scoparium) and increased available soil nitrogen and biomass of forbs. This effect may explain why the grass-feedingP. nebrascensis had a positive effect on the forb-feedingM. femur-rubrum on unfertilized plots. Overall, we show that direct effects of consumers on resources can predict competition and other important indirect interactions within a community.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566967
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  • 6
    Electronic Resource
    Electronic Resource
    Interspecific competition among grasshoppers and their effect on plant abundance in experimental field environments (1992)
    Springer
    Oecologia 89 (1992), S. 524-532 
    Details
    ISSN: 1432-1939
    Keywords: Grasshoppers ; Interspecific competition ; Food limitation ; Nitrogen ; Indirect mutualism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We tested whether grasshoppers in experimental field environments, i.e. cages (40×40 cm) placed on existing old field vegetation, (1) were limited in density by plant abundance and/or nitrogen content, (2) exhibited interspecific competition, and (3) altered the relative abundance of different plant species. We examined interactions among a pair of early season grasshopper species (May–June; Arphia conspersa and Pardalophora apiculata) and a late season pair (July–August; Melanoplus femur-rubrum and Melanoplus bivittatus). Each grasshopper species was placed in cages by itself and with another grasshopper species. Grasshoppers generally survived at higher density in fertilized cages and they reduced plant abundance relative to empty cages, suggesting that grasshoppers may be food limited at these densities. In unfertilized plots, early season grasshoppers preferred grasses (Schizachyrium scoparium and Poa pratensis) and favored the growth of forbs (especially Solidago spp.). However, late in summer, Melanoplus spp. preferred Solidago spp. and favored the growth of grasses. The pattern of grasshopper survivorship and plant reduction within these experimental environments provide preliminary support for some of the predictions of resource competition theory. Grasshoppers exhibited interspecific competition only if they significantly reduced plant biomass. If two species competed, a grasshopper species was eliminated only if the superior competitor, when living by itself, could reduce plant biomass to a significantly lower level than the inferior competitor. Competitors persisted only if they did not differ in their ability to reduce plant biomass or reduced the abundance of different plant species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317159
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  • 7
    Electronic Resource
    Electronic Resource
    Plant succession and gopher disturbance along an experimental gradient (1983)
    Springer
    Oecologia 60 (1983), S. 285-292 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A field was disturbed via disking, divided into 36 plots, and fertilized with different ratios of N:Mg in 1980. High N:Mg supply ratios tended to favor the perennial grasses Agrostis scabra and Agropyron repens over annual plants. In 1981 the experimental field was invaded by a fossorial mammalian herbivore, the plains pocket gopher, Geomys bursarius. Geomys bursarius was significantly more active in plots dominated by Agrostis scabra and Agropyron repens. The gopher mounds it created were dominated by the annual grass Setaria glauca and the annual herb Polygonum convolvulus. Thus the direct effect of resource competition among these plants was counteracted by the indirect response of an herbivore to the treatments. Although nitrogen fertilization tended to increase the rate of successional replacement of annuals by perennials, the indirect response of gophers to nitrogen tended to slow the rate of succession. This suggests that herbivore responses to spatial variation in plant community composition and productivity may be an important determinant of the rate of succession and the species diversity of the community.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00376840
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  • 8
    Electronic Resource
    Electronic Resource
    Species effects on nitrogen cycling: a test with perennial grasses (1990)
    Springer
    Oecologia 84 (1990), S. 433-441 
    Details
    ISSN: 1432-1939
    Keywords: Nitrogen cycling ; Species effects ; Grasses Litter quality ; N mineralization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary To test for differing effects of plant species on nitrogen dynamics, we planted monocultures of five perennial grasses (Agropyron repens, Agrostis scabra, Poa pratensis, Schizachyrium scoparium, and Andropogon gerardi) on a series of soils ranging from sand to black soil. In situ net N mineralization was measured in the monocultures for three years. By the third year, initially identical soils under different species had diverged up to 10-fold in annual net mineralization. This divergence corresponded to differences in the tissue N concentrations, belowground lignin concentrations, and belowground biomasses of the species. These results demonstrate the potential for strong feedbacks between the species composition of vegetation and N cycling. If individual plant species can affect N mineralization and N availability, then competition for N may lead to positive or negative feedbacks between the processes controlling species composition and ecosystem processes such as N and C cycling. These feedbacks create the potential for alternative stable states for the vegetation-soil system given the same initial abiotic conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00328157
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  • 9
    Electronic Resource
    Electronic Resource
    Oscillations and chaos in the dynamics of a perennial grass (1991)
    [s.l.] : Nature Publishing Group
    Nature 353 (1991), S. 653-655 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] When ecologists sample populations, the resulting relationships are often blurred. This variance may result from sampling error and environmental variation or from deterministic processes that yield oscillations or chaos8-11. Although it is difficult to distinguish between noise and chaos9,10, ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/353653a0
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  • 10
    Electronic Resource
    Electronic Resource
    Plant diversity enhances ecosystem responses to elevated CO 2 and nitrogen deposition (2001)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 410 (2001), S. 809-810 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Human actions are causing declines in plant biodiversity, increases in atmospheric CO2 concentrations and increases in nitrogen deposition; however, the interactive effects of these factors on ecosystem processes are unknown. Reduced biodiversity has raised numerous concerns, ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35071062
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