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Herbivory

Herbivory. Monarch caterpillar and Milkweed leaf. Plant Resource Defense. Qualitative defense - highly toxic substances, small doses of which can kill predators

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Herbivory

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  1. Herbivory Monarch caterpillar and Milkweed leaf

  2. Plant Resource Defense • Qualitative defense - highly toxic substances, small doses of which can kill predators • high nutrient environment/fast growth (high turnover in plants) - use toxins (plant secondary compounds) that often require N, expensive to make (must be replaced often), but can be made rapidly - cyanide compounds, cardiac glycosides, alkaloids - small molecules

  3. Plant Resource Defense • Quantitative defense - substances that gradually build up inside an herbivore as it eats and prevent digestion of food • low nutrient environment/slow growth (low turnover in plants) - primarily use carbon structures - wood, cellulose, lignin, tannins - large molecules - makes plant hard or unpleasant to eat (woodiness, silica), but plants are slow to make these defenses

  4. Induced Defenses • Another aspect of plant defenses is that plants do not always have tissues loaded with defensive chemicals - in many plants, defensive chemicals are only produced when they are needed, usually after the plant has experienced some herbivory - this is an induced defense

  5. Induced defenses in Birch Trees

  6. Induced defenses in Birch Trees

  7. Rubus prickles

  8. Acacia depanolobium

  9. Giraffe and Acacia

  10. Plant defenses are developed at a cost to fitness when: 1. Organisms evolve more defenses if they are exposed to much damage and fewer defenses if cost of defense is high 2. More defenses are allocated within an organism to valuable tissues that are at risk 3. Defense mechanisms are reduced when enemies are absent and increased when plants are attacked - mostly true for chemicals not structures 4. Defense mechanisms are costly and cannot be maintained if plants are severely stressed by environmental factors

  11. Pine beetle infestation – British Columbia

  12. Pine Beetle and Pitch Tube

  13. Serengeti Grazing System

  14. Serengeti Grazing System

  15. Serengeti Grazing System • 1 million wildebeest • 600,000 Thomson’s gazelles • 200,000 zebra • 65,000 Cape buffalo • Unknown numbers of 20 other species of large grazing mammals • 36 species of rodents • 38 species of grasshoppers • Area of about 23,000 square kilometers

  16. Thomson’s Gazelle

  17. More Large Grazers

  18. Serengeti Grazing System

  19. Grazing facilitation • Grazing facilitation occurs when the feeding activity of one herbivore species improves the food supply for a second species

  20. Opuntia stricta – prickly pear

  21. Prickly pear infestation in Australia

  22. Area infested with prickly pear before biocontrol

  23. Same area after biocontrol

  24. Biocontrol Agent – Cactoblastis cactorum

  25. Summary of Ecological Effects of Herbivores • Herbivores can affect plant fitness: • Reduce plant growth rate • Reduce plant reproduction: • Directly by preying on seeds • Indirectly by reducing plant growth

  26. Summary of Ecological Effects of Herbivores • Herbivores may control plant distribution and abundance

  27. Summary of Ecological Effects of Herbivores • Through alterations of plant distribution and abundance, herbivores can alter plant community structure and composition

  28. Summary of Ecological Effects of Herbivores • The effects of herbivores on plants depends on the degree of feeding specialization of the herbivore

  29. Feeding Specializations

  30. Feeding Specializations- high crowned teeth Bos – cow; Bison – bison; m3 – third molar

  31. Symbiosis

  32. Symbiosis • Symbioses - species living in close association • Parasitism +,- parasite benefits, host harmed • Commensalism +,0 or 0,0 can have positive effect for one species or for neither • Mutualism +,+ both species benefit

  33. Gopher Tortoise – Commensal Host

  34. Gopher Tortoise Distribution

  35. Epiphytes Bird’s Nest Fern

  36. Nalini Nadkarni studying epiphytes

  37. Epiphytes Figure 1: Hypothetical tree illustrating how vascular epiphytes in humid forests tend to partition substrates illustrating sensitivity to micro climate, particularly humidity, and associated development of the organic rooting media required by some populations.

  38. Redwood Epiphyte Ecosystem

  39. Parasitism and Disease Lyme Disease Cycle in the UK

  40. Parasitism • Parasitism - intimate association between two species in which the parasite obtains its nutrients from a host - parasite usually causes some degree of harm to its host - either reduced growth or reproduction • Pathogen – disease causing agent • Disease – abnormal condition of host due to infection by a pathogen that impairs physiological functioning

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