plant defenses

Plant defensesPlant defenses► Mechanical protection on leaf surfaceMechanical protection on leaf surface► Secondary ChemistrySecondary Chemistry

Polymers or silica crystals that reduce Polymers or silica crystals that reduce digestibilitydigestibility Chemical toxins that kill or repel at very low Chemical toxins that kill or repel at very low concentrationsconcentrations

► Low nutrient concentrations (a defense Low nutrient concentrations (a defense or consequence of physiological limitation?)or consequence of physiological limitation?)

Mechanical ProtectionMechanical Protection

►Spines Spines ►TrichomesTrichomes► Glandular hairsGlandular hairs

e.g., cactus, cotton, field beanse.g., cactus, cotton, field beans

Chemical warfareChemical warfare

► “ “Herbivores are between the devil Herbivores are between the devil and the deep blue sea”and the deep blue sea”

Digestibility ReducersDigestibility Reducers

►Cell wall components: cellulose and Cell wall components: cellulose and hemicellulosehemicellulose

► TanninsTannins Free in cytoplasmFree in cytoplasm Block action of digestive enzymesBlock action of digestive enzymes Bind to proteins being digestedBind to proteins being digested Interfer with protein activity in gut wallInterfer with protein activity in gut wall

► reduced growth rate, weight loss, reduced growth rate, weight loss, malnutrition.malnutrition.

ToxinsToxins

ToxinsToxins• HCN• 1,000 plant species sequester•3.5 mg/kg body mass = death•Blocks action of cytochrome oxidase•Cooking removes HCN (e.g. almonds)

Constitutive vs. Induced Constitutive vs. Induced DefensesDefenses

► Cost Cost ► e.g., Lignin vs. Proteinase inhibitorse.g., Lignin vs. Proteinase inhibitors

block catalytic activity of proteiolytic block catalytic activity of proteiolytic enzymes in animal gut by binding to enzymes in animal gut by binding to active site of enzyme moleculeactive site of enzyme molecule

Eating PlantsEating Plants

► “ “the plant world is not colored green; the plant world is not colored green; it is colored morphine, caffeine, tannin, it is colored morphine, caffeine, tannin, phenol, terpene, latex, … and L-dopa”phenol, terpene, latex, … and L-dopa”

Feeding specialization and Feeding specialization and plant defensesplant defenses

► PolyphagousPolyphagous► OligophagousOligophagous► MonophagousMonophagous

Eating PlantsEating Plants

► Mechanical breakdownMechanical breakdown► Microbial farmsMicrobial farms

Eating animals that eat plantsEating animals that eat plants

Ecology of HerbivoryEcology of Herbivory

► Is herbivory always bad?Is herbivory always bad?► Life history traits associated with Life history traits associated with

levels of herbivorylevels of herbivory► Co-evolutionary arms raceCo-evolutionary arms race

N-addition Treatment

Unfertilized Bulk Exponential

Seed

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Unfertilized Bulk Exponential

Bio

mass

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Unfertilized Bulk Exponential

Flo

wer

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Pod M

ass

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12

a a

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ab b

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d,e d

ea

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Ecology of HerbivoryEcology of Herbivory

► Apparency hypothesisApparency hypothesis► Resource Availability hypothesisResource Availability hypothesis

(carbon:nutrient balance hypothesis)(carbon:nutrient balance hypothesis)

Ecology of HerbivoryEcology of Herbivory

Ecology of HerbivoryEcology of Herbivory

Ecology of HerbivoryEcology of Herbivory