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Plant defenses

Plant defenses. Mechanical protection on leaf surface Secondary Chemistry Polymers or silica crystals that reduce digestibility Chemical toxins that kill or repel at very low concentrations Low nutrient concentrations (a defense or consequence of physiological limitation?).

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Plant defenses

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  1. Plant defenses Mechanical protection on leaf surface Secondary Chemistry Polymers or silica crystals that reduce digestibility Chemical toxins that kill or repel at very low concentrations Low nutrient concentrations (a defense or consequence of physiological limitation?)

  2. Mechanical Protection • Spines • Trichomes • Glandular hairs e.g., cactus, cotton, field beans

  3. Chemical warfare • “Herbivores are between the devil and the deep blue sea”

  4. Digestibility Reducers • Cell wall components: cellulose and hemicellulose • Tannins • Free in cytoplasm • Block action of digestive enzymes • Bind to proteins being digested • Interfer with protein activity in gut wall • reduced growth rate, weight loss, malnutrition.

  5. Toxins

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

  7. Constitutive vs. Induced Defenses • Cost • e.g., Lignin vs. Proteinase inhibitors block catalytic activity of proteiolytic enzymes in animal gut by binding to active site of enzyme molecule

  8. Eating Plants • “the plant world is not colored green; it is colored morphine, caffeine, tannin, phenol, terpene, latex, … and L-dopa”

  9. Feeding specialization and plant defenses • Polyphagous • Oligophagous • Monophagous

  10. Eating Plants • Mechanical breakdown • Microbial farms

  11. Eating animals that eat plants

  12. Ecology of Herbivory • Is herbivory always bad? • Life history traits associated with levels of herbivory • Co-evolutionary arms race

  13. Ecology of Herbivory • Apparency hypothesis • Resource Availability hypothesis (carbon:nutrient balance hypothesis)

  14. Ecology of Herbivory

  15. Ecology of Herbivory

  16. Ecology of Herbivory

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