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  • 1
    Digitale Medien
    Digitale Medien
    A neighbourhood approach to self-thinning (1983)
    Springer
    Oecologia 56 (1983), S. 381-384 
    Details
    ISSN: 1432-1939
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The fate of individual plants of Helianthus annuus was monitored in populations sown at a density of 650 seeds m-2. Ninety six percent of the seeds germinated but only fifty two percent of the seedlings survived to the end of the experiment due to self-thinning. Whilst the seedlings emerged over only four days the cotyledons then took up to eight days to emerge from the seed case and open fully. The survival of individuals depended primarily on cotyledon-opening time but plants which occupied very small areas (〈900 mm2) at germination were also less likely to survice. The increased likelihood of mortality amongst the late germinating individuals was probably as a result of shade from older, larger neighbours. It is suggested that one-sided interference for light during self-thinning will increase the importance of early establishment relative to neighbour effects in determining the survival of plants except at very high levels of crowding. The complex of environmental and genetic factors acting to maximise the growth rate of the very young seedling relative to its neighbours will clearly play an important part in determining the position of a plant in the size hierarchy of a population.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00379716
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Tiller dynamics and self-thinning in grassland habitats (1983)
    Springer
    Oecologia 60 (1983), S. 390-395 
    Details
    ISSN: 1432-1939
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The tiller dynamics and weight-density relationships of grasses were investigated in sown monocultures and in an established grassland both in full light and under shade. Monocultures of Festuca pratensis and Lolium perenne sown at high densities conformed to the-3/2 Power Law during establishment, but once the maximum standing had been reached the trajectory of the thinning line switched to a slope of approximately-1 when weight was plotted against density on logarithmic scales. Subsequently the populations showed a cyclical pattern of tiller weight and density bound by a line related to the maximum standing crop but also close to the-3/2 thinning line. The natural populations also showed a cyclical pattern of tiller weight and density at combinations very similar to those in the sown monocultures and close to a thinning line with an intercept (log c) of 4.4–4.7 assuming the generality of the -3/2 Power Law as w=cN -3/2. Tiller dynamics were very similar on all the plots despite differences in the species composition of each plot. The greatest seasonal variation in tiller number occurred under the shade of birch trees, perhaps due to resource depletion caused by the tree canopy during late summer and the presence of tree litter during the winter. The artificial shade treatment had little effect on plant yield but caused a significant change in the composition of the vegetation. It is suggested that mixed populations of grasses behave in essentially the same fashion as monocultures and that vegetational change might be analysed as a multispecies participation in a mutual cyclical proces of tiller death and regeneration.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00376857
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Rhizosphere and root-infecting fungi and the design of ecological field experiments (1995)
    Springer
    Oecologia 102 (1995), S. 230-237 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Rhizosphere fungi ; Root-infecting fungi ; Fungicide ; Vulpia ciliata ssp. ambigua ; Annual plant performance
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract As part of a wider study into the role of soil fungi in the ecology of the winter annual grass, Vulpia ciliata ssp. ambigua (Le Gall) Stace & Auquier, we applied the fungicides benomyl and prochloraz to three natural populations of the grass growing in East anglia, United Kingdom. The rhizosphere and rootinfecting fungi associated with the three populations were analysed each month between February and May 1992 when plants set seed. There were marked differences between the fungal floras associated with each of the three populations of V. ciliata, despite the fact that associated plant species and soil nutrient status were broadly similar between sites. This was attributed to wide differences in soil pH between the three populations. Prochloraz did not affect fungal abundance, but benomyl decreased the isolation frequencies of Fusarium oxysporum from roots and the frequencies of Penicillium and Trichoderma spp. isolated from rhizosphere soil, and increased the frequency of isolation of Mucor hiemalis from the rhizosphere of V. ciliata. There were also significant increases in the isolation frequencies of F. oxysporum from roots and M. hiemalis, Trichoderma spp. and Phoma fimeti from the rhizosphere of V. ciliata as plants matured. The significance of these results for the design of ecological field experiments are discussed in light of a previous study which has shown that asymptomatic root-infecting fungi can affect plant fecundity and hence abundance in natural populations of V. ciliata. We propose that differences in microbial communities between sites, controlled in part by soil chemistry, are a major factor determining plant performance under field conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00333255
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Habitat switching by dark-bellied brent geese Branta b. bernicla (L.) in relation to food depletion (1995)
    Springer
    Oecologia 103 (1995), S. 499-508 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Algae ; Brent geese ; Grass pasture ; Saltmarsh ; Switching
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Seasonal changes in the distribution and feeding behaviour of dark-bellied brent geese Branta b. bernicla (L.) and the biomass of their food plants were studied in three successive winters on the Norfolk coast. The data was used, in conjunction with published information, to show how depletion, productivity and mortality of food plants drive the pattern of habitat switching in this species. It is then possible to explain the habitat shifts observed over the last 35 years and predict future changes. On arrival, geese fed first on algal beds and then on salt marsh, grass and arable fields before returning to feed entirely on the salt marsh in spring. The biomass of green algae, and subsequently the salt marsh vegetation, declined during the autumn and this could be attributed to depletion through goose grazing and natural mortality. As depletion occurred the geese fed more intensively, for a greater percentage of time and with an increasing pace rate, the net result, however, was a declining intake rate (as measured by defaecation rate). The algal biomass at which the geese switched from the algal beds to salt marsh was consistent between years, with heavy storm-induced loss of algae in one year resulting in an earlier switch. That the timing of habitat switches may be explained by depletion of food plants was further supported by historical data: the number of brent geese wintering at the site has increased dramatically over the last 30–35 years and the time of switching from algal beds to salt marsh and from salt marsh to salt marsh and fields has become progressively earlier, as expected from the increased depletion. The expected further increase in brent goose numbers will increase the rate of depletion of intertidal vegetation so that the switches between habitats will be more rapid and the geese will move inland earlier and remain inland longer. The expected increase in the brent goose population will thus result in a disproportionate increase in the levels of conflict between brent geese and agriculture.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00328689
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Ecotypic differentiation of response to enhanced CO2 and temperature levels in Arabidopsis thaliana (1995)
    Springer
    Oecologia 104 (1995), S. 394-396 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Arabidopsis thaliana ; Global environmental change ; Ecotypic variation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Five ecotypes of Arabidopsis thaliana, from widely dispersed origins, were grown under combinations of ambient and elevated atmospheric CO2 concentrations and ambient and elevated temperatures within solardomes. Total above-ground plant biomass was measured when the majority of plants across all ecotypes and treatments had formed seed pods. There were substantial differences in biomass between the ecotypes across all treatments. Temperature had no effect on biomass whilst CO2 had a significant effect both alone and in interaction with ecotype. The CO2 x ecotype interaction was mostly due to the enhancement of a single ecotype from the Cape Verde Islands.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00328376
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Host selectivity and the mediation of competition by the root hemiparasite Rhinanthus minor (1991)
    Springer
    Oecologia 86 (1991), S. 81-87 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Competition ; Hemiparasitism ; Host selectivity ; Rhinanthus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Rhinanthus minor (Yellow-rattle) was grown in replacement series mixtures with Lolium perenne and Trifolium repens. The hemiparasitic interaction resulted in Relative Yield Totals (the sum of the yields in mixture relative to those in monoculture) considerably above 2. The hemiparasite caused a greater decrease in the yield of the legume and also performed better on the legume, indicating that T. repens was a better host for R. minor than L. perenne under the experimental conditions. When L. perenne and T. repens were grown in binary mixture with or without R. minor the hemiparasite affected considerably the competitive relationship between the two species by selectively parasitizing the legume. The effect of R. minor on competition between the two species was, however, dependent upon the nutrient status of the soil: the higher the level of soil nitrogen the fewer haustorial connections were made with T. repens and the less was the depression in its yield. In another series of experiments in which Festuca rubra, Holcus lanatus and L. perenne were grown in various binary mixtures with or without R. minor it was also shown that the yield of a preferred host was depressed to the advantage of a non-preferred host. It is suggested that the mediation of competition by the hemiparasite provides a mechanism by which it might affect the structure and diversity of plant communities.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00317393
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    The role of the hemiparasitic annual Rhinanthus minor in determining grassland community structure (1992)
    Springer
    Oecologia 89 (1992), S. 62-68 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Rhinanthus ; Hemiparasitism ; Species diversity ; Community structure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Rhinanthus minor (yellow-rattle) is a widespread hemiparasitic plant of grassland habitats throughout Great Britain. It is usually considered to be indicative of species-rich grassland, but in a survey of 14 habitats throughout Britain it was found that R. minor at the time of flowering normally occupied relatively low-diversity patches within areas of high diversity as determined by the number of species, Simpson's Index and the Shannon-Wiener Index. Following the death of adult plants of R. minor in the summer it was shown that the pattern of species diversity changed such that by the time R. minor germinated in the following spring the differences between the areas containing and not containing R. minor were much less distinct. A perturbation experiment in which R. minor was removed from four sites indicated that the effect of the removal of R. minor on the development of community structure over the next year was to increase species diversity on three of the sites and decrease it on the fourth. Those species which responded to the removal of R. minor by an increase in abundance were shown to be preferred hosts. All three lines of evidence point to the fact R. minor has a significant effect on the species diversity of the communities in which it grows by selectively parasitizing components of the flora and modifying the competitive relationships between plants. However, as the communities generally responded to the removal of R. minor by an increase in diversity and as the general survey indicated that R. minor is generally associated with areas of low diversity it would appear that the plants which are selectively parasitized are generally not the competitive dominants in the community.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00319016
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    On the analysis of competition at the level of the individual plant (1987)
    Springer
    Oecologia 71 (1987), S. 308-317 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Competition ; Population density ; Emergence time ; Yield ; Annuals
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The extent to which some measure of local crowding can account for the performance of individual plants is examined with reference to populations of two species of annual plant. Only a relatively small proportion of the variation in individual plant yield could be accounted for by measures of local crowding. These included the number of close neighbours, an estimate of the area available to each plant and competitive pressure. A multiple regression that took account of both emergence time and local crowding increased the proportion of variance that could be accounted for up to 50%. Computer simulations of the growth of indivudual plants in monoculture were then caried out in order to determine whether the unexplained variation resulted from fundamental flaws in the models or from unaccounted for sources of variation in the field. The results from the simulations again indicated that only a relatively low proportion of the variation in individual plant yield could be accounted for by emergence time and local density, even though these were known to be the only variables present. These findings are discussed in relation to the relative importance of one-sided and two-sided competition, and the complex cross-correlations that occur between individuals in plant populations. These two factors will make it very difficult for field workers to determine accurately what factors determine individual plant yield and in particular to predict the effects of local crowding on the performance of individual plants.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00377300
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    The host range and selectivity of a parasitic plant: Rhinanthus minor L. (1989)
    Springer
    Oecologia 78 (1989), S. 401-406 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Rhinanthus ; Hemiparasitism ; Host selectivity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Rhinanthus minor (Yellow-rattle) is a widespread hemiparasitic plant of grassland habitats throughout Britain. Association analysis of the dune vegetation at Holme-next-the-Sea in eastern England revealed only two potential host plants through positive association. In contrast direct examination of the root systems revealed haustorial connections with 20 host species. The number of species parasitized by one plant ranged from one to seven. Data from another four sites in Britain and one in central Europe indicate that the natural host range of R. minor encompasses at least 50 species from 18 families with 22% in the Leguminosae and 30% in the Gramineae. Comparison of the number of haustorial connections made to each species with the abundance of roots in the soil shows that R. minor is a highly selective parasite, but that the selectivity is not consistent between populations or between plants from different parts of the same population. The reasons for host selectivity are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00379116
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Population biology of salt marsh and sand dune annuals (1985)
    Springer
    Plant ecology 62 (1985), S. 487-497 
    Details
    ISSN: 1573-5052
    Schlagwort(e): Annual plant ; Demography ; Distribution ; Phenology ; Population model
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Annuals represent a significant component of the vegetation of coastal salt marshes and sand dunes. From many points of view, the two habitats might appear to have little in common. Yet both are characterized by episodes of low water potential, marked spatial and temporal heterogeneity and a zonation which, within certain limits, reflects successional change. There are also similarities of distribution. Annuals are dominant usually in the pioneer stages; the Salicornia-dominated low marsh areas are perhaps analogues with strandline ephemeral populations (e.g. Cakile maritima) on the fore-dunes. In mature stages, annuals are associated with small gaps in the matrix of perennials, at least some of these arising from drought or disturbance. Nevertheless populations can reach very high densities. The most striking contrast is phenological; only summer annuals are found on marshes, whereas winter annuals predominate on dunes (except for the strandline). Similarly there is a difference in species richness. Rather few species of annual are typical of marshes while a great many are found on dunes. Properties of the seed bank, survival, reproduction and population regulation are compared in marsh and dune annuals, with special reference to Cakile, Salicornia, Rhinanthus and Vulpia. Interpretations are suggested which take account of environmental predictability and heterogeneity. Finally, the general applicability of simple mathematical models of these populations in the different coastal habitats is considered.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00044776
    Standort Signatur Erwartet Verfügbarkeit
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