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Asymmetric Competition

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John Connolly – One of the best experts on this subject based on the ideXlab platform.

  • Asymmetric Competition between plant species
    Oecologia, 1996
    Co-Authors: John Connolly, Peter M. Wayne

    Abstract:

    Despite extensive interest in the role of plant size in Competition, few formal attempts have been made to quantify the magnitude of Asymmetric Competition, particularly for interactions between members of different species. This paper introduces the concept of Asymmetric interspecific Competition at the population livel (i.e. mean plant performance) in mixtures of species. It proposes an index of interspecific competitive asymmetry which allows for a progressively greater Asymmetric effect as the average size differences between competing species increase, and allows for such an effect whether individuals of focal species are larger or smaller, on average, than competitors. This index of competitive asymmetry is evaluated in the study of interactions between two widely coexisting annuals of disturbed habitats, Stellaria media and Poa annua. An experiment was conducted in which the density, relative frequency and relative seedling sizes (emergence times) of Poa and Stellaria individuals were varied. The relative growth rate (RGR) for both species was measured over a 22-day period. An inverse linear model was fitted for each species, relating the RGR of the focal species to the initial biomass of each species. Each response model included an asymmetry coefficient (β) to assess whether the impact of a unit of initial biomass of the associate species changed with the relative sizes of seedlings of the two species. A zero value of β implies symmetric Competition between the two populations; i.e. the competitive effect of a unit of associate species biomass does not change with its initial seedling size. If β is positive the smaller the initial relative size of seedlings of the associate species, the smaller their per unit biomass effect on the response of the focal species. The model fitted our data for Stellaria and Poa well and was validated by an alternative modelling approach. Asymmetry coefficients were estimated as 0.508 (P

  • Asymmetric Competition between plant species
    Oecologia, 1996
    Co-Authors: John Connolly, Peter M. Wayne

    Abstract:

    Despite extensive interest in the role of plant size in Competition, few formal attempts have been made to quantify the magnitude of Asymmetric Competition, particularly for interactions between members of different species. This paper introduces the concept of Asymmetric interspecific Competition at the population livel (i.e. mean plant performance) in mixtures of species. It proposes an index of interspecific competitive asymmetry which allows for a progressively greater Asymmetric effect as the average size differences between competing species increase, and allows for such an effect whether individuals of focal species are larger or smaller, on average, than competitors. This index of competitive asymmetry is evaluated in the study of interactions between two widely coexisting annuals of disturbed habitats, Stellaria media and Poa annua. An experiment was conducted in which the density, relative frequency and relative seedling sizes (emergence times) of Poa and Stellaria individuals were varied. The relative growth rate (RGR) for both species was measured over a 22-day period. An inverse linear model was fitted for each species, relating the RGR of the focal species to the initial biomass of each species. Each response model included an asymmetry coefficient (β) to assess whether the impact of a unit of initial biomass of the associate species changed with the relative sizes of seedlings of the two species. A zero value of β implies symmetric Competition between the two populations; i.e. the competitive effect of a unit of associate species biomass does not change with its initial seedling size. If β is positive the smaller the initial relative size of seedlings of the associate species, the smaller their per unit biomass effect on the response of the focal species. The model fitted our data for Stellaria and Poa well and was validated by an alternative modelling approach. Asymmetry coefficients were estimated as 0.508 (P<0.05) for the effect of Poa in the Stellaria model, and 0.0001 (NS) for the effect of Stellaria in the Poa model; i.e. the effect of Poa on Stellaria was Asymmetric while the effect of Stellaria on Poa was symmetric. Differences in interspecific species Asymmetric competitive effects are discussed within the context of shoot architecture, and the relative importance of Competition for light versus soil resources. Finally, we discuss the relationship of this model to earlier models of competitive asymmetry, and consider the implications of interspecific competitive asymmetry for a number of current theories of plant Competition and community organisation.

Sarah P. Otto – One of the best experts on this subject based on the ideXlab platform.

  • Asymmetric Competition impacts evolutionary rescue in a changing environment
    Proceedings of The Royal Society B: Biological Sciences, 2017
    Co-Authors: Courtney L. Van Den Elzen, Elizabeth J. Kleynhans, Sarah P. Otto

    Abstract:

    Interspecific Competition can strongly influence the evolutionary response of a species to a changing environment, impacting the chance that the species survives or goes extinct. Previous work has shown that when two species compete for a temporally shifting resource distribution, the species lagging behind the resource peak is the first to go extinct due to competitive exclusion. However, this work assumed symmetrically distributed resources and Competition. Asymmetries can generate differences between species in population sizes, genetic variation and trait means. We show that Asymmetric resource availability or Competition can facilitate coexistence and even occasionally cause the leading species to go extinct first. Surprisingly, we also find cases where traits evolve in the opposite direction to the changing environment because of a ‘vacuum of competitive release’ created when the lagging species declines in number. Thus, the species exhibiting the slowest rate of trait evolution is not always the most likely to go extinct in a changing environment. Our results demonstrate that the extent to which species appear to be tracking environmental change and the extent to which they are preadapted to that change may not necessarily determine which species will be the winners and which will be the losers in a rapidly changing world.

  • Evolving Communities One Species Simulations All Raw Simulation Data
    , 2017
    Co-Authors: Courtney L. Van Den Elzen, Elizabeth J. Kleynhans, Sarah P. Otto

    Abstract:

    WARNING: ~ 4.38 GB when expanded. Contains all of the raw data from the one-species simulations from the manuscript “Asymmetric Competition Impacts Evolutionary Rescue in a Changing Environment”.

  • Evolving Communities Two Species Raw Data (Part 1 – Symmetric Resources and Sym and Asym Competition)
    , 2017
    Co-Authors: Courtney L. Van Den Elzen, Elizabeth J. Kleynhans, Sarah P. Otto

    Abstract:

    WARNING: ~ 3.6 GB when expanded. Contains all raw simulation data for the two-species simulations with symmetric resource distribution and Competition from the manuscript “Asymmetric Competition Impacts Evolutionary Rescue in a Changing Environment”.

Peter M. Wayne – One of the best experts on this subject based on the ideXlab platform.

  • Asymmetric Competition between plant species
    Oecologia, 1996
    Co-Authors: John Connolly, Peter M. Wayne

    Abstract:

    Despite extensive interest in the role of plant size in Competition, few formal attempts have been made to quantify the magnitude of Asymmetric Competition, particularly for interactions between members of different species. This paper introduces the concept of Asymmetric interspecific Competition at the population livel (i.e. mean plant performance) in mixtures of species. It proposes an index of interspecific competitive asymmetry which allows for a progressively greater Asymmetric effect as the average size differences between competing species increase, and allows for such an effect whether individuals of focal species are larger or smaller, on average, than competitors. This index of competitive asymmetry is evaluated in the study of interactions between two widely coexisting annuals of disturbed habitats, Stellaria media and Poa annua. An experiment was conducted in which the density, relative frequency and relative seedling sizes (emergence times) of Poa and Stellaria individuals were varied. The relative growth rate (RGR) for both species was measured over a 22-day period. An inverse linear model was fitted for each species, relating the RGR of the focal species to the initial biomass of each species. Each response model included an asymmetry coefficient (β) to assess whether the impact of a unit of initial biomass of the associate species changed with the relative sizes of seedlings of the two species. A zero value of β implies symmetric Competition between the two populations; i.e. the competitive effect of a unit of associate species biomass does not change with its initial seedling size. If β is positive the smaller the initial relative size of seedlings of the associate species, the smaller their per unit biomass effect on the response of the focal species. The model fitted our data for Stellaria and Poa well and was validated by an alternative modelling approach. Asymmetry coefficients were estimated as 0.508 (P

  • Asymmetric Competition between plant species
    Oecologia, 1996
    Co-Authors: John Connolly, Peter M. Wayne

    Abstract:

    Despite extensive interest in the role of plant size in Competition, few formal attempts have been made to quantify the magnitude of Asymmetric Competition, particularly for interactions between members of different species. This paper introduces the concept of Asymmetric interspecific Competition at the population livel (i.e. mean plant performance) in mixtures of species. It proposes an index of interspecific competitive asymmetry which allows for a progressively greater Asymmetric effect as the average size differences between competing species increase, and allows for such an effect whether individuals of focal species are larger or smaller, on average, than competitors. This index of competitive asymmetry is evaluated in the study of interactions between two widely coexisting annuals of disturbed habitats, Stellaria media and Poa annua. An experiment was conducted in which the density, relative frequency and relative seedling sizes (emergence times) of Poa and Stellaria individuals were varied. The relative growth rate (RGR) for both species was measured over a 22-day period. An inverse linear model was fitted for each species, relating the RGR of the focal species to the initial biomass of each species. Each response model included an asymmetry coefficient (β) to assess whether the impact of a unit of initial biomass of the associate species changed with the relative sizes of seedlings of the two species. A zero value of β implies symmetric Competition between the two populations; i.e. the competitive effect of a unit of associate species biomass does not change with its initial seedling size. If β is positive the smaller the initial relative size of seedlings of the associate species, the smaller their per unit biomass effect on the response of the focal species. The model fitted our data for Stellaria and Poa well and was validated by an alternative modelling approach. Asymmetry coefficients were estimated as 0.508 (P<0.05) for the effect of Poa in the Stellaria model, and 0.0001 (NS) for the effect of Stellaria in the Poa model; i.e. the effect of Poa on Stellaria was Asymmetric while the effect of Stellaria on Poa was symmetric. Differences in interspecific species Asymmetric competitive effects are discussed within the context of shoot architecture, and the relative importance of Competition for light versus soil resources. Finally, we discuss the relationship of this model to earlier models of competitive asymmetry, and consider the implications of interspecific competitive asymmetry for a number of current theories of plant Competition and community organisation.