Weed Evolution Patterns evolutionary development:Patterns evolutionary development: –Resource allocation: organisms can budget energy or resources to successfully complete life cycleorganisms can budget energy or resources to successfully complete life cycle plants must divide resources among organs (shoots, roots, leaves, reproductive tissues)plants must divide resources among organs (shoots, roots, leaves, reproductive tissues) –amount of time spent on growth, maintenance, and dormancy important to insure success several theories, but all recognize importance of resource allocation for species survival and community developmentseveral theories, but all recognize importance of resource allocation for species survival and community development

Weed Evolution Patterns evolutionary development:Patterns evolutionary development: –r & K selection: (resource allocation) most widely accepted conceptmost widely accepted concept logistic equation (Lotka 1925; Volterra 1926)logistic equation (Lotka 1925; Volterra 1926) –dN/dt = rN(K-N/K) »dN/dt = change in pop over time »r is innate capacity for pop increase in unlimited environment and equals birthrate minus death rate (a constant) »N is the pop size »K is the highest pop that can be maintained in a constant but limited (real) environment; i.e. the carrying capacity

Weed Evolution Patterns evolutionary development:Patterns evolutionary development: –r & K selection: (resource allocation) r & K selection implies that organisms lie on a continuum between the two extremes of resource allocation that represent the two extremes for survivalr & K selection implies that organisms lie on a continuum between the two extremes of resource allocation that represent the two extremes for survival –extreme r –extreme K

Weed Evolution Patterns evolutionary development :Patterns evolutionary development : –r & K selection: (resource allocation) extreme r selection leads to short-lived plants that occur in open habitats & early successional stagesextreme r selection leads to short-lived plants that occur in open habitats & early successional stages –large % of resources (biomass) allocated to reproduction –population regulated by abiotic factors extreme K selection leads to long-lived plants w/prolonged vegetative stage, late successional stagesextreme K selection leads to long-lived plants w/prolonged vegetative stage, late successional stages –allocate small % resources (biomass) to reproduction –population near carrying capacity –population regulated biotic factors few if any plant species at extremes!few if any plant species at extremes!

Weed Evolution C, S, and R selection (Grime, 1977; Evidence for the existence of three primary strategies in plants and its relevance to ecological and evolutionary theory. Am. Nat. 111: ):C, S, and R selection (Grime, 1977; Evidence for the existence of three primary strategies in plants and its relevance to ecological and evolutionary theory. Am. Nat. 111: ): –extension of r and K continuum 2 basic factors limit plant material in any environment2 basic factors limit plant material in any environment –stress »external phenomena that limit production –disturbance »partial or total disruption of plant biomass – as with r and K, spectrum of this continuum varies widely »4 outcomes if examine the extremes

Weed Evolution - C,S, and R selection: Intensity of disturbance: Intensity of stress: High: Low: High: Low: Plant death Stress Stresstolerators Ruderals Competitors

Weed Evolution C, S, and R selection:C, S, and R selection: –stress tolerators decrease allocations toward vegetative growth & reproductiondecrease allocations toward vegetative growth & reproduction have characteristics to allow survival of relatively mature individuals in harsh environmenthave characteristics to allow survival of relatively mature individuals in harsh environment limitations caused by physical factorslimitations caused by physical factors –seasonal floods, drought, competition found in continually unproductive environments late stages successionfound in continually unproductive environments late stages succession

Weed Evolution C, S, and R selection:C, S, and R selection: –Competitors maximize resource capture in productive but relatively undisturbed environmentsmaximize resource capture in productive but relatively undisturbed environments exhibit extensive vegetative growth phaseexhibit extensive vegetative growth phase abundant in early and intermediate successional stages.abundant in early and intermediate successional stages.

Weed Evolution C, S, and R selection:C, S, and R selection: –Ruderals occur in highly disturbed, but potentially productive environmentsoccur in highly disturbed, but potentially productive environments short-lived herbaceous plants with high seed outputshort-lived herbaceous plants with high seed output early stages of successionearly stages of succession

Weed Evolution C, S, and R selection:C, S, and R selection: –Grime mapped vegetation using triangular ordination of selection pressures: competition, disturbance, stress

A=annual herbs B=biennial herbs C=perennial herbs & ferns D=trees & shrubs E=lichens F=bryophytes

Weed Evolution C, S, and R selection:C, S, and R selection: –Grime mapped vegetation using triangular ordination of selection pressures: competition, disturbance, stress annual herbs in ruderal cornerannual herbs in ruderal corner Lichens in stress cornerLichens in stress corner shrubs, trees stress tolerant to competitiveshrubs, trees stress tolerant to competitive no plant entirely competitiveno plant entirely competitive –some herbaceous perennials, trees, shrubs directed toward competitive strategy

Weed Evolution Weeds as strategists:Weeds as strategists: –weeds possess characteristics common to competitors & ruderals herbaceous annuals, biennials, and some herbaceous perennials follow pattern combining competitors & ruderalsherbaceous annuals, biennials, and some herbaceous perennials follow pattern combining competitors & ruderals trees and shrubs more closely aligned with characteristics associated with stress- tolerant competitor patterntrees and shrubs more closely aligned with characteristics associated with stress- tolerant competitor pattern

Weed Evolution Weeds as strategists:Weeds as strategists: –Competitive ruderals found on productive sites where dominance by true competitors decreased because of disturbancefound on productive sites where dominance by true competitors decreased because of disturbance –expect occasional disturbance, but continual/frequent disturbance favors ruderals conditions favorable to CR, when disturbance occurs once or twice during life cycle but does not affect or eliminate allconditions favorable to CR, when disturbance occurs once or twice during life cycle but does not affect or eliminate all

Weed Evolution Weeds as strategists:Weeds as strategists: –Competitive ruderals found: meadows, grasslands subject to seasonal disturbance (grazing)meadows, grasslands subject to seasonal disturbance (grazing) floodplains (non-seasonal or not frequent)floodplains (non-seasonal or not frequent) eroded areaseroded areas lake and ditch marginslake and ditch margins arable landarable land

Weed Evolution Weeds as strategists:Weeds as strategists: –Competitive ruderals expected to have: rapid early growth raterapid early growth rate competition begins before floweringcompetition begins before flowering optimize resource capture to maximize dry matter and seed productionoptimize resource capture to maximize dry matter and seed production –e.g. common ragweed, velvetleaf, annual ryegrass, Canada thistle, quackgrass, Russian knapweed, leafy spurge...

Weed Evolution Weeds as strategists:Weeds as strategists: –Competitive ruderals most herbaceous weeds of arable land adapted to CR strategymost herbaceous weeds of arable land adapted to CR strategy –as ruderals, would be expected to need disturbance to establish »particularly ag disturbance –cannot continually disturb ag environment and raise crops »these CR plants would be expected to be adapted to competitive strategy to survive –in ‘natural habitats’ arable weeds may have been ruderals »ag allowed them to be more successful

Weed Evolution Weeds as strategists:Weeds as strategists: –Stress tolerant competitors examine succession to understandexamine succession to understand –initial colonization followed by progressive small change over time w/vegetation replacement –forest succession »shrubs occupy early & intermediate succession; i.e. CR strategists »eastern forests, deciduous spp. late seral »western forests, buckbrush, alder, RM maple are CR strategists »notably shade intolerant and replaced by shade tolerant conifers - late seral