O`dB dB° @@@ @@@@ÿÿÿÿJrHMÁdBÀdC EN DB dC     &;+ 3 'KþÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿWeiner, J. Thomas, S.C. 1986>7Size variability and competition in plant monocultures. Oikos47211-222 OIKOS Weiner<6review, asymmetric competition, size structure, models,%Makes the argument that plants compete asymmetrically and form size hierarchies through competition. 14 out of 16 studies supported that competition is asymmetric because high density plants had higher levels of variation than low density plants. Variation increases until self-thinning, then can decrease.Emphasizes how the generation of plant size distributions will ultimately be determined by the RGR, as modified by resource depletion and other biotic and abiotic environmental factors. Some modeling: single plants grow logistically. Competition is modelled through a matrix of competition coefficients, subject to constant yield law, in a Lodka-Volterra type way. Result: Gini does not increase with density. If plant resource acquisition is modeled one-sided, variation does increase with` Bergelson1995 Carrere1999 Chapman1996 Parsons1995 Parsons1996 Parsons1996 Parsons1996 Parsons1999 Parsons1999 Schwinning1996Ì Schwinning1996Ì Schwinning1996Ì Schwinning1996Ì Schwinning1999Ì Schwinning1999ÌThornley1995Ì yt.€zhSuodlc mo eabkct ohtsip parel tare .hTre'e s aol tfor veeiiwgno htrew ro knilcduni ght eaJapenes sna dmeipirac lerustl.sae rrgwohtp sh ena dht eitema thwci hrgwohtl vele sfo.fT ehesp ramatere sam yon tebc roeralet dost ah tisezr naikgn sam yon tebr teiaen dvorel noeg repirdo sfot mi.eT ih sam yxelpia nhw yon-nrcwoed dlpnastd notos oh w aisngficina tocrrletaoi nebwtee niseza dng ortw hnircmene.tla lisezd fiefercnseb teewnes eeldnisga tht enoes tfoc moepititnoa erm gainifdei tn oalgr eidff Authors Journals Keywords .                               ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿ Ü  Alves, S.J.ÌÌ Bergelson, J.Campos Lustosa, S.B.Ì Carrere, P.ÌÌ Chapman, D.FÌde Faccio, P.C.ÌÌ deMoraes, A.Ì Nabinger, C.ÌParsons, A. J.ÌÌÌ Parsons, A.J.Schwinning, S.ÌÌÌThornley, J. H. M.ÌÌÌ „ 79-94$://A1995QG522000116/Thornley, J. H. M. Bergelson, J. Parsons, A. J.LEComplex Dynamics in a Carbon-Nitrogen Model of a Grass Legume PastureAnnals of Botanyþ÷model, grass, legume, competition, coexistence, carbon, nitrogen, fixation, instability, chaos continuously grazed mixture; plant animal interactions; permanent pasture; trifolium-repens; white clover; sward; performance; physiology; leaves; urine~wA physiologically based model of a grass-legume pasture is used to study the dynamics of these competing species. In our model, we consider carbon and nitrogen pools and fluxes, incorporating competition for light and soil mineral nitrogen, and including the processes of nitrogen fixation, nitrogen losses and dry matter allocation. First, the steady-state responses of each species to nitrogen deposition, to leaching rate, and to other nitrogen losses are examined. We then consider the dynamic behaviour of these species when there is no time delay for nitrogen cycled through the soil organic matter pool. Next, the effects of various time delays associated with the soil organic matter nitrogen pool on the system dynamics are examined: the behaviour becomes complex, non-linear and exhibits lightly or heavily damped oscillations at two frequencies. The high sensitivity of the system both to the initial Value of the soil organic matter nitrogen pool, and to any photosynthetic competitive advantage, is investigated. The implications of these results in relation to observations and experiments on grass-legume pastures are discussed.t 1995 Janu751 ISI:A1995QG52200011c  DAnnals of BotanyÌFunctional EcologyÌÌÌJournal of EcologyÌÌÌ  L.asymmetric competitionÌÌÌbite dimensionsÌÌ cattleÌÌÌ\Wcellular automaton, metapopulation dynamics, pattern formation, population oscillationsÌÌ competitionÌÌ continuously grazed mixtureÌÌ crop growthÌÌ defoliationÌÌ densityÌÌdiet selectionÌÌÌhediet selection, nitrogen cycle, pasture composition, plant population dynamics, spatial heterogeneity dynamicsÌ ecosystemsÌÌÌ environmentsÌ growthÌÌÌherbage intakeÌÌÌ herbivoresÌÌÌ leavesÌÌÌlightlolium-perenneÌÌÌ mixed swardsÌmodeld^model, grass, legume, competition, coexistence, carbon, nitrogen, fixation, instability, chaosÌÌÌ monoculturesÌnitrogen-fixation patternÌÌ patternsÌhcPennisetum americanum 'Custer', mode of competition, size structure dynamics, plant growth analysisÌÌperennial ryegrassÌÌÌ performanceÌÌpermanent pasturephotosynthesisÌÌÌ physiologyÌÌÌplant animal interactionsplant-populations qualityÌÌsheep sheep urineÌÌsward systemsÌÌtemperate grassland swardtrifolium-repensÌtrifolium-repens lÌÌÌurine variabilityÌÌ white clover̦@ ¬ ¤80*Chapman, D.F Parsons, A.J. Schwinning, S. 1996\UManagement of clover in grazed pastures: expectations, limitations and opportunities.rhaWhite Clover: New Zealand's Competitive Edge. Symposium of the New Zealand Grassland Association.ÿ  Lincoln, N.Z 55-640)Parsons, A.J. Carrere, P. Schwinning, S.  19992,Dynamics of heterogeneity in a grazed sward. RLdeMoraes, A. Nabinger, C. de Faccio, P.C. Alves, S.J. Campos Lustosa, S.B.LFInternational Symposium on Grassland Ecophysiology and Grazing Ecology Curitiba, Parana, Brazil187-214ÿ799-813$://A1996WB58300001$Schwinning, S. Parsons, A. J.XQAnalysis of the coexistence mechanisms for grasses and legumes in grazing systemsHJournal of Ecology*$diet selection, nitrogen cycle, pasture composition, plant population dynamics, spatial heterogeneity continuously grazed mixture; temperate grassland sward; plant animal interactions; white clover; diet selection; perennial ryegrass; mixed swards; nitrogen-fixation; crop growth; sheep urinetm1 It is widely assumed that grass-legume associations offer a way to sustainable, low input land use, with reduced environmental impact. However, a combination of both ecological and physiological principles may be needed to understand the sustainability of species balances.2 To increase understanding of grass-legume dynamics, we developed a model that extends a recently proposed pasture model (Thornley, Bergelson & Parsons: Annals of Botany 1995, 75, 79-94) by including selective grazing and spatial considerations, Population oscillations were shown to stem from the way grasses can exploit leguminous N fixation. If the legume is a relatively good competitor for light, populations do not oscillate near equilibrium, but in the converse case, populations do oscillate.3 Large amplitude oscillations can arise when there are sufficiently long time delays in the plant populations' responses to changes in the competitive environment. In the present model, these stem from variable internal substrate pools (of C and N), which uncouple biosynthesis from resource uptake, but other time delay mechanisms are easily envisaged.4 Urine deposits prevent the establishment of equilibrium within patches, but spatially random urine deposition stabilizes population fluctuations at the field scale. This is because perturbations to local N cycles desynchronize patches with regard to the grass-legume population cycle.5 Differences in the soil N environment (fertilizer input, leaching rate) determine whether the species can coexist, but where coexistence is possible, species composition regulates soil mineral N.6 Selective grazing (herbivory) does not essentially alter the grass-legume interaction, but complex foraging trade-offs lead to herbivory effects that may seem counterintuitive. The model has important implications for attempts to control the legume content of mixed species communities. 1996 Dec846ISI:A1996WB58300001815-826$://A1996WB58300002t$Schwinning, S. Parsons, A. J.jcA spatially explicit population model of stoloniferous N-fixing legumes in mixed pasture with grassÌJournal of EcologyÎÇcellular automaton, metapopulation dynamics, pattern formation, population oscillations trifolium-repens l; white clover; dynamics; sheep; pattern; environments; competition; systems; quality; growthrÆ¿1 In a previous paper, we outlined the physiological prerequisites for population oscillations between a grass and a nitrogen-fixing legume, such as clover. Here, we examine the field-scale consequences of patch-scale oscillations in legume content, using a cellular automaton with variable hierarchy between the two species.2 We define cell states in the automaton by species content and soil N status. Grass-legume oscillations at the patch scale are represented as an alternation between states of grass dominance (high N) and legume dominance (low N). To this physiologically based population oscillation, we add local extinctions of legume and state-dependent success in legume invasion.3 Legume populations oscillate at the field scale, given arbitrary initial conditions. However, spatially random perturbations to the soil N status (e.g. urine) establishes a pasture structure that dampens the field scale oscillation. The stabilizing pasture structure comprises moving patches of legume dominance. This pattern was not predicted by our previous, purely physiological model.4 The model highlights that a patchy species distribution does not in itself mean the species is dispersal limited. In this model, changing the dispersal ability of legumes plays only a limited role in determining their proportion in the mixture. Legume abundance depends as much on the rate at which favourable (low N) sites become available for invasion.5 Seasonal disturbances that act uniformly across the field, such as winter (legume) mortality and/or springtime fertilizer application, can lead to sustained field scale variations in legume content that are only partly explained by the level of seasonal disturbance itself. Another large part is explained by previous years' legume contents. Pastures may therefore exhibit a 'memory' for legume performance which helps to explain the perceived 'unpredictability' of some grass-legume associations.6 We argue that legume dynamics in mixed pastures cannot be fully understood without combining ecological and physiological concepts of species interactions at three different scales: competitive interactions at the patch-scale, dispersal at the between-patch scale, and seasonality at the field-scale.Ì 1996 DecÌ846ÌISI:A1996WB58300002Ì 47-57$://A1996TR78600006Schwinning, S.PJDecomposition analysis of competitive symmetry and size structure dynamicsAnnals of BotanyèáPennisetum americanum 'Custer', mode of competition, size structure dynamics, plant growth analysis plant-populations; asymmetric competition; growth; variability; model; density; monocultures; patterns; light; photosynthesisengAn analysis is introduced, based on the decomposition of relative growth rates, to examine the mode of competition (i.e. whether competition is symmetric or asymmetric), the size-dependence of growth, and their interdependence. In particular, the basis for two commonly held Views is examined: (1) that the type of resource limitation determines the mode of competition, and (2) that asymmetric competition always leads to size-divergence between unequal competitors. It is shown that in held-grown miller plants, competition for light was symmetric at low density and asymmetric at high density. However, size variation at low density decreased during growth, because small plants had greater relative growth rates than larger plants. Size variation stayed constant at high density, since plants of all sizes had equal average relative growth rates. Based on these results and a general discussion, it is proposed that the type of resource limitation does not determine the mode of competition. Competition for light can be symmetric, and foraging for heterogeneously distributed soil resources can produce asymmetric competition below-ground. Furthermore, the mode of competition alone does not determine size structure dynamics. Size-dependence of resource conversion efficiency and allocation can modify the effects of resource uptake on growth. (C) 1996 Annals of Botany CompanyÌ 1996 Janm771gISI:A1996TR78600006s737-747$://000084788600001o$Schwinning, S. Parsons, A. J.^XThe stability of grazing systems revisited: spatial models and the role of heterogeneityFunctional Ecologyš“temperate grassland sward; bite dimensions; lolium-perenne; diet selection; herbage intake; cattle; defoliation; ecosystems; herbivores; physiology  1999 Decn136mISI:000084788600001o