Density Effects on the Size Structure of Annual Plant Populations: An Indication of Neighbourhood Competition

Bonan, Gordon B.

doi:10.1093/oxfordjournals.aob.a088262

Cited by 72 publications

(54 citation statements)

References 19 publications

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“…Some studies have concluded that a major factor generating size variation in crowded plant populations is the "size asymmetry" of competition: larger plants have a disproportionate advantage (for their relative size) in competition with smaller plants, suppressing their growth (Begon 1984;Weiner 1990;Schwinning and Weiner 1998). In simple models, increases in size inequality with density are observed only when competition is size asymmetric (Weiner and Thomas 1986), so the commonly observed increase in size inequality in populations grown at higher densities has been considered evidence in support of the hypothesis of size-asymmetric competition (Weiner 1990).Other researchers have argued that the importance of size-asymmetric competition has been exaggerated, and its existence has even been questioned (Turner and Rabinowitz 1983;Bonan 1991). Other phenomena, such as variation in exponential growth rates and variation in local crowding, might explain the patterns of size variation that have been attributed to size-asymmetric competition, such as the higher size inequality observed at higher densities.…”

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The Effects of Density, Spatial Pattern, and Competitive Symmetry on Size Variation in Simulated Plant Populations

Weiner¹,

Stoll²,

Muller‐Landau³

et al. 2001

The American Naturalist

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Patterns of size inequality in crowded plant populations are often taken to be indicative of the degree of size asymmetry of competition, but recent research suggests that some of the patterns attributed to size-asymmetric competition could be due to spatial structure. To investigate the theoretical relationships between plant density, spatial pattern, and competitive size asymmetry in determining size variation in crowded plant populations, we developed a spatially explicit, individual-based plant competition model based on overlapping zones of influence. The zone of influence of each plant is modeled as a circle, growing in two dimensions, and is allometrically related to plant biomass. The area of the circle represents resources potentially available to the plant, and plants compete for resources in areas in which they overlap. The size asymmetry of competition is reflected in the rules for dividing up the overlapping areas. Theoretical plant populations were grown in random and in perfectly uniform spatial patterns at four densities under size-asymmetric and size-symmetric competition. Both spatial pattern and size asymmetry contributed to size variation, but their relative importance varied greatly over density and over time. Early in stand development, spatial pattern was more important than the symmetry of competition in determining the degree of size variation within the population, but after plants grew and competition intensified, the size asymmetry of competition became a much more important * E-mail: jw@kvl.dk. † E-mail: stoll@sgi.unibe.ch. ‡ E-mail: helene@eno.princeton.edu. § E-mail: ajasen@concentric.net. source of size variation. Size variability was slightly higher at higher densities when competition was symmetric and plants were distributed nonuniformly in space. In a uniform spatial pattern, size variation increased with density only when competition was size asymmetric. Our results suggest that when competition is size asymmetric and intense, it will be more important in generating size variation than is local variation in density. Our results and the available data are consistent with the hypothesis that high levels of size inequality commonly observed within crowded plant populations are largely due to size-asymmetric competition, not to variation in local density.Keywords: asymmetric competition, individual-based models, population structure, size inequality, spatial effects, zone of influence.Competition among individuals usually increases size variation within plant populations, but there is controversy over the mechanisms through which this occurs. This controversy reflects a fundamental disagreement about the nature of competition among individual plants. Some studies have concluded that a major factor generating size variation in crowded plant populations is the "size asymmetry" of competition: larger plants have a disproportionate advantage (for their relative size) in competition with smaller plants, suppressing their growth (Begon 1984;Weiner 1990;Schwinning and Weiner 1...

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The Effects of Density, Spatial Pattern, and Competitive Symmetry on Size Variation in Simulated Plant Populations

Weiner¹,

Stoll²,

Muller‐Landau³

et al. 2001

The American Naturalist

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“…Além disso, estas mesmas plantas apresentaram maior estatura. Conforme Bonan (1991), as flutuações em tamanho de plantas caracterizam as condições em que se desenvolveram, sendo as maiores estaturas relacionadas com maiores densidades de semeaduras, que proporciona maior competição entre indivíduos. Assim, no cultivo a campo as plantas de trigo foram submetidas a maiores níveis A B Figura 1.…”

Section: Resultsunclassified

“…Assim, no cultivo a campo as plantas de trigo foram submetidas a maiores níveis A B Figura 1. Diagrama de correlações entre a ordem de emergência das plantas, diâmetro do pseudocolmo, comprimento da bainha foliar (estatura) e a escala de desenvolvimento foliar, determinada conforme Haun (1973), no colmo principal (Haun CP) e nos afilhos do coleóptilo (Haun A0), da primeira folha (Haun A1), da segunda folha (Haun A2) e da terceira folha (Haun A3), que em conjunto formam o somatório foliar por planta (Haun soma (Benjamin & Hardwick 1986, Bonan 1991. Assim, para se ter uma comparação válida entre os ambientes (campo e canteiros) seria necessário uma maior área de amostragem no cultivo a campo.…”

Section: Resultsunclassified

“…Se todas as plantas iniciam o crescimento com a mesma massa, no mesmo dia, presume-se que a disponibilidade de recursos e a taxa de crescimento individual variam de acordo com a área disponível para cada planta, na população (Benjamin & Hardwick 1986). Por isso, uma parcela de variabilidade de produção entre plantas pode ser explicada pela flutuação de densidade ou assimetria de espaçamento entre plantas, que ocorre na mesma população (Bonan 1991). Neste contexto, pequenos estresses ou diferenças na habilidade competitiva das plantas, em população, podem ser decisivos na determinação individual de produção, uma vez que as plantas perdem a capacidade de compensação para o rendimento.…”

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Parâmetros da habilidade competitiva no estabelecimento de populações caracterizam o potencial de produção individual em trigo e aveia

Santos¹,

Mundstock²

2002

Rev. bras. Bot.

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(Parameters of competitive ability in the establishment of populations characterise the individual yield potential in wheat and oat). Variation in production among plants is normally observed in monocultures and it can occur since the establishment of the populations by their competitive ability. This work was performed with the aim of selecting the parameters of competitive ability during the initial growth that are related to yield potential at the end of development. Plants of wheat (EMBRAPA 16) and oat (UFRGS 15) were grown on masons and field conditions and correlation among morphological parameters during the tillering and bloom stages were followed. During tillering, our results revealed that the pseudoculm diameter and leaf development were relevant to define the competitive ability by high correlation with dry mass, independently of species and environment. In these populations, the sequence of emergency of plants was inversely related to the apical development (to inflorescence) and to parameters that defined the competitive ability. This initial competitive ability was directly related to the size and yield potential (spikelets per inflorescence) of plants at the bloom stage. Our results indicate that the individual yield potential can be predicted by measurement of non destructive parameters of the competitive ability in the early stages of plant development.RESUMO (Parâmetros da habilidade competitiva no estabelecimento de populações caracterizam o potencial de produção individual em trigo e aveia). Em monoculturas, normalmente se observa uma variação de produção entre plantas, que pode estar ocorrendo desde o estabelecimento da população, pela habilidade competitiva destas. Este trabalho foi desenvolvido com o objetivo de selecionar parâmetros de habilidade competitiva, durante o estabelecimento, que se relacionam com o potencial de produção, no final do desenvolvimento. Plantas de trigo (EMBRAPA 16) e aveia (UFRGS 15) foram cultivadas em canteiros e a campo, correlacionando-se parâmetros morfológicos, nos estádios de afilhamento e florescimento. No afilhamento, nossos resultados revelaram que o diâmetro do pseudocolmo e o desenvolvimento foliar foram os parâmetros mais relevantes na caracterização da habilidade competitiva, pela alta associação com a massa seca, independente da espécie e do ambiente. Nestas populações, a ordem com que as plantas emergiram foi inversamente relacionada com o estádio de desenvolvimento apical (para inflorescência) e com os parâmetros que definiram a habilidade competitiva. Esta habilidade de competição inicial foi diretamente relacionada com o tamanho e a potencialidade de produção (espiguetas por inflorescência) das plantas, no estádio de florescimento. Os resultados indicam que o potencial de produção individual pode ser estimado por medidas de parâmetros não destrutivos, da capacidade de competição, nos primeiros estádios de desenvolvimento das plantas.Key words -Triticum aestivum, Avena sativa, competitive ability, yield potential IntroduçãoQuando se es...

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“…Studies of competitive symmetry have shown that larger size may confer a disproportionate advantage for resource preemption (reviews in Weiner, 1990;Casper and Jackson, 1997;Schwinning and Weiner, 1998) which can affect the size distribution of individuals in crowded populations (e.g. Weiner, 1985;Weiner et al, 2001; but see Bonan, 1991). The benefits of larger size are also evident in studies of competitive ability (e.g.…”

Section: Introductionmentioning

confidence: 99%

Biomass explains the intensity of facilitative – not competitive – interactions: three intraspecific tests with annuals

Ariza¹,

Tielbӧrger²

2012

Web Ecol.

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Abstract. Despite efforts to discern the role of plant size in resource competition, the circumstances under which size-dependent plant-plant interactions occur are still unclear. The traditional assumption is that competition intensifies with increasing neighbour size. However, recent studies suggest that the size (biomass) dependence of competitive interactions is strongest at very low biomass levels and becomes negligible after a certain threshold neighbour biomass has been reached. We searched for the generality of such patterns for three common annual plant species in Israel. We monitored target and neighbour biomass along their entire lifecycle using an even-aged, intraspecific and intrapopulation competition screenhouse experiment under water-limited conditions. For all focal species, neighbour presence had a net negative effect on vegetative biomass at harvest. However, this was not explained by increasing neighbour biomass over time, as a consistent pattern of sizedependent facilitative, rather than competitive, interactions was observed at all life stages. We explain these observations in terms of co-occurring aboveground facilitation and dominant belowground competition for water. Since our findings are the first of their kind and contradict theoretical predictions of biomass dependence of net negative interactions, we advocate further experiments addressing size dependence in interactions among plants. In particular, theoretical models addressing size dependence of positive interactions must be developed.

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Density Effects on the Size Structure of Annual Plant Populations: An Indication of Neighbourhood Competition

Cited by 72 publications

References 19 publications

The Effects of Density, Spatial Pattern, and Competitive Symmetry on Size Variation in Simulated Plant Populations

The Effects of Density, Spatial Pattern, and Competitive Symmetry on Size Variation in Simulated Plant Populations

Parâmetros da habilidade competitiva no estabelecimento de populações caracterizam o potencial de produção individual em trigo e aveia

Biomass explains the intensity of facilitative – not competitive – interactions: three intraspecific tests with annuals

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