L` dd0dd@ @@@ @@@@~UAPddP EN DB P     & . 67FRj : spatial models and the role of heterogeneityFunctional Ecologytemperate grassland sward; bite dimensions; lolium-perenne; diet selection; herbage intake; cattle; defoliation; ecosystems; herbivores; physiology  1999 Decn136mISI:000084788600001oiet selectionherbage intake\ Fox1995 Hara20020 Jasentuliyana2001 Muller2002a Muller-Landau2001 Muller-Landau2002 Schwinning1994 Schwinning1995 Schwinning1996 Schwinning1998 Stoll2001 Stoll2002 Weiner1990 Weiner19981 Weiner2001 Weiner200230 Zak2003ms20030 Zak2003ms20030 Zak2003ms20030 Zak200330 Zak2003ms20030 Zak2003ms20030 Zak2003ms20030 Zak20030030 Zak2003ms20030 Zak20030030 Zak2003ms20030 Zak2003ms20030 Zak20030030 Zak2003ms20030 Zak20030030 Zak2003ms20030 Zak2003 Zak2003ms20030 Zak2003ms20030 Zak2003ms20030 Zak20030030 Zak2003ms20030 Zak20030030 Zak2003ms20030 Zak2003ms20030 Zak20030030 Zak2003 4066696C75534C656E446E7F64554C6C6972627172594C5E435670627F206E656E0C0000000 Authors!Journals Keywords x                                4! Carrere, P. Davis, K.Ehleringer, J. R. Fay, P. A. Fox, G. A.Gebauer, R. L. E. Haddad, B. M. Hara, T. Harte, J. Huxman, T. E.Jasentuliyana, A. Knapp, A. K. Lin, G. H. Loik, M. E. Muller, E.Muller-Landau, H.Parsons, A. J.Pockman, W. T.Richardson, L.Rosenzweig, M. L.Schwinning, S.Schwinning, Susanne Shaw, M. R. Small, E. E. Smith, M. D. Smith, S. D. Starr, B. I. Stoll, P. Tissue, D. T. Weiner, J.Weltzin, J. F.Williams, D. G. Zak, J. C.   American NaturalistAnnals of Botany Bioscience EcologyFunctional EcologyGrass and Forage ScienceJournal of Ecology OecologiaOikosLGProceedings of the Royal Society of London Series B-Biological Sciences Trends in Ecology & Evolution  dxabutilon-theophrasti annuals arabidopsisarid ecosystempjarid ecosystems, plant functional types, precipitation pulse use, stable isotope label, water partitioningasymmetric competitionzasymmetric competition, individual-based models, population structure, size inequality, spatial effects, zone of influenceTPasymmetric competition, morphological plasticity, self-thinning, shade avoidance asymmetryAtriplex confertifolia, Chrysothamnus nauseosus, Colorado plateau, desert, Gutierrezia sarothrae, neighbor removal, plant competition, resource pulses, stable isotopes, water uptake availabilitybiosphere modelbite dimensions carbon-isotope discrimination cattle\Wcellular automaton, metapopulation dynamics, pattern formation, population oscillationschihuahuan desertclimate-change coexistencecold desert communitycold-desert perennialscolorado plateau community competition continuously grazed mixture crop growth defoliation density desert shrubsPJdesert, genetic algorithm, plant functional types, whole-plant carbon gain\Ydeuterium-labeled irrigation, niche separation, precipitation change, rain use efficiencydiet selectionhediet selection, nitrogen cycle, pasture composition, plant population dynamics, spatial heterogeneity dynamics ecosystem ecosystems elevated co2 environments fitness geometry germinationDAglobal change, community, ecosystem, precipitation, soil moisturegrass grassesgrazing systems growthheavy precipitationherbage intake herbivores@:herbivory, spatial, scaling, heterogeneity, grazing, modelindividual growth individuals interferencelightlocal interferencelolium-perenne mechanisms mixed swardsmodel monoculturesmorphological plasticityn-15 natural-abundanceneighborhood competitionneighborhood models neighbors nitrogennitrogen-fixation pasture pattern patternshcPennisetum americanum 'Custer', mode of competition, size structure dynamics, plant growth analysisperennial ryegrassphotosynthesisphotosynthetic capacity physiology phytochromeplant animal interactionsplant-populations plantsprimary productivity qualityrainfall eventsresource acquisition|yresource competition, allometry of growth and resource uptake, plasticity, spatial patterns, competition in clonal plantsroot communication root systemsseedling establishmentsheep sheep urineshortgrass steppe shrubs signalsize hierarchiessoil soil nutrient heterogeneity soil-moisturesoil-water dynamicssonoran desertspecies modelsspecies-diversity standsstomatal conductancestructure dynamics succulentssummer precipitationsward systemstemperate grassland sward temperaturetemporal dynamicstreestrifolium-repens l united-states variability vegetationvegetation distributionwater water-uptake water-use white clover @$Schwinning, Susannet 1994F@Effects of competitive symmetry on populations of annual plants.& Ecology and Evolutionary Biology Tucson University of Arizonas Ph.D.l422-432$://A1995RH16000015 Schwinning, S. Fox, G. A.NHPopulation-Dynamic Consequences of Competitive Symmetry in Annual Plants Oikosdneighborhood models; size hierarchies; species models; monocultures; interference; variability; coexistence; fitness; environments; germinationoAsymmetric competition is a form of resource division among plants, in which large plants greatly suppress the growth of smaller neighbors. In annual plants, small size differences between seedlings at the onset of competition are magnified into large differences in seed-set by asymmetric competition. We formulate a novel neighborhood model, which reflects this seedling size effect as modified by the type of competitive symmetry. In the model, competition type is represented by a single, biologically meaningful parameter. We implement the model in a population growth model for two species, one at low density (the invader), and one at high density (the resident). The species are the same, except for their seedling biomass distributions. Under these conditions, we find that asymmetric competition always favors invasion by the species with lager average seedling size, but impairs invasion by the other species. Based on this invasibility criterion, we conclude that asymmetric competition always favors competitive exclusion in our model. However, by modifying some of the model assumptions, we suggest scenarios in which asymmetric competition may promote coexistence. 1995 Apr723ISI:A1995RH16000015 47-57$://A1996TR78600006Schwinning, S.PJDecomposition analysis of competitive symmetry and size structure dynamicsAnnals of BotanyPennisetum americanum 'Custer', mode of competition, size structure dynamics, plant growth analysis plant-populations; asymmetric competition; growth; variability; model; density; monocultures; patterns; light; photosynthesisengAn analysis is introduced, based on the decomposition of relative growth rates, to examine the mode of competition (i.e. whether competition is symmetric or asymmetric), the size-dependence of growth, and their interdependence. In particular, the basis for two commonly held Views is examined: (1) that the type of resource limitation determines the mode of competition, and (2) that asymmetric competition always leads to size-divergence between unequal competitors. It is shown that in held-grown miller plants, competition for light was symmetric at low density and asymmetric at high density. However, size variation at low density decreased during growth, because small plants had greater relative growth rates than larger plants. Size variation stayed constant at high density, since plants of all sizes had equal average relative growth rates. Based on these results and a general discussion, it is proposed that the type of resource limitation does not determine the mode of competition. Competition for light can be symmetric, and foraging for heterogeneously distributed soil resources can produce asymmetric competition below-ground. Furthermore, the mode of competition alone does not determine size structure dynamics. Size-dependence of resource conversion efficiency and allocation can modify the effects of resource uptake on growth. (C) 1996 Annals of Botany Company 1996 Janm771gISI:A1996TR78600006s447-455$://000072196300001e Schwinning, S. Weiner, J.sVOMechanisms determining the degree of size asymmetry in competition among plants Oecologia`Zresource competition, allometry of growth and resource uptake, plasticity, spatial patterns, competition in clonal plants soil nutrient heterogeneity; cold-desert perennials; morphological plasticity; seedling establishment; resource acquisition; abutilon-theophrasti; local interference; root communication; structure dynamics; individual growthWhen plants are competing, larger individuals often obtain a disproportionate share of the contested resources and suppress the growth of their smaller neighbors, a phenomenon called size-asymmetric competition. We review what is known about the mechanisms that give rise to and modify the degree of size asymmetry in competition among plants, and attempt to clarify some of the confusion in the literature on size asymmetry. We broadly distinguish between mechanisms determined primarily by characteristics of contested resource from those that are influenced by the growth and behavior of the plants themselves. To generate size asymmetric resource competition, a resource must be "pre-emptable." Because of its directionality, light is the primary, but perhaps not the only, example of a pre-emptable resource. The available data. suggest that competition for mineral nutrients is often size symmetric (i.e., contested resources are divided in proportion to competitor sizes), but the potential role of patchily and/or episodically supplied nutrients in causing size asymmetry is largely unexplored. Virtually nothing is known about the size symmetry of competition for water. Plasticity in morphology and physiology acts to reduce the degree of size asymmetry in competition. We argue that an allometric perspective on growth, allocation, resource uptake, and resource utilization can help us understand and quantify the mechanisms through which plants compete. 1998 Feb 1134ISI:000072196300001 2191-2195e$://000179245700002\@:Stoll, P. Weiner, J. Muller-Landau, H. Muller, E. Hara, T.HASize symmetry of competition alters biomass-density relationshipsNGProceedings of the Royal Society of London Series B-Biological Sciencesasymmetric competition, morphological plasticity, self-thinning, shade avoidance plant-populations; phytochrome; arabidopsis; mechanisms; neighbors; asymmetry; geometry; signal; standsAs crowded populations of plants develop, the growth of some plants is accompanied by the death of others, a process called density-dependent mortality or 'self-thinning'. During the course of density-dependent mortality, the relationship between total population biomass (B) and surviving plant density (N) is allometric: B = aN(b). Essentially, increasing population biomass can be achieved only through decreasing population density. Variation in the allometric coefficient a among species has been recognized for many years and is important for management, assessment of productivity and carbon budgets, but the causes of this variation have not been elucidated. Individual-based models predict that size-dependent competition causes variation in the allometric coefficient. Using transgenic Arabidopsis with decreased plasticity, we provide experimental evidence that morphological plasticity of wild-type populations decreases the size asymmetry of competition for light and thereby decreases density-dependent mortality. This decrease in density-dependent mortality results in more biomass at a given density under size-symmetric compared with size-asymmetric competition.e 2002 Nov 7i 269b 1506ISI:000179245700002n 360-364$://A1990ED99500005f Weiner, J.2+Asymmetric Competition in Plant-Populationsi$Trends in Ecology & Evolution 1990 Nov511ISI:A1990ED99500005t438-450$://000171003600009>8Weiner, J. Stoll, P. Muller-Landau, H. Jasentuliyana, A.xrThe effects of density, spatial pattern, and competitive symmetry on size variation in simulated plant populationsAmerican NaturalistSasymmetric competition, individual-based models, population structure, size inequality, spatial effects, zone of influence neighborhood competition; asymmetric competition; structure dynamics; growth; model; monocultures; variability; individuals; mechanisms; interferencePatterns 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 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. 2001 Oct 1584ISI:000171003600009