BIOS 5970: Plant-Herbivore Interactions Dr. Stephen Malcolm, Department of Biological Sciences Week 5. Plant defense theory 2: Development: Lecture summary: Resource Availability Theory: Coley, Bryant and Chapin (1985). Based on:» Janzen (1974).» McKey et al. (1978).» McKey (1984). Carbon:Nitrogen (Nutrient) Balance Theory: Bryant, Chapin and Klein (1983). Other views: Fox (1981). BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 1
2. Resource Availability Theory: Coley, Bryant and Chapin (1985): Defensive capabilities of plants are constrained by the resources available to them. While apparency theory implies that herbivore foraging efficiency strongly influences plant defense, resource availability theory assumes that inherent growth physiology, photosynthetic capability, and nutrient availability determine the amounts and kinds of defense that plants use. BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 2
3. Resource Availability Theory: 3 variables influence amounts and kinds of defense investment: (1) Inherent growth rate. (2) Overall resource availability. (3) Carbon/nitrogen balance. Result in: (1) High or low investment in defense. (2) Immobile (e.g. lignins or tannins = quantitative) or, mobile defenses (e.g. terpenoids, alkaloids = qualitative). (3) Carbon-based (e.g. lignins, tannins, terpenoids), or nitrogen-based (e.g. alkaloids, cyanogens, nonprotein amino acids). BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 3
4. Resource Availability Theory: These ideas are directly based on: Janzen, D.H. 1974. Tropical blackwater rivers, animals, and mast fruiting of the Dipterocarpaceae. Biotropica 6(2): 69-103. and the test of his ideas by: McKey, D., Waterman, P.G., Mbi, C.N., Gartlan, J.S., and Struhsaker, T.T. 1978. Phenolic content of vegetation in two African rain forests: Ecological implications. Science 202: 61-64. BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 4
5. Janzen (1974): Tropical blackwater rivers run through nutrient-poor, sandy soils. Plants have high concentrations of chemical defenses (turn water dark brown) because they grow slowly and need to protect scarce resources. Blackwater tributary of Rio Napo, Peru, 4 Oct 2009 BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 5
6. Janzen (1974): Thus Janzen argued that plants should have: (1) Tough foliage heavily defended by chemicals. (2) Minimal herbivory. (3) Low numbers and low biomass of herbivores. (4) Rare top carnivores because herbivores are uncommon. BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 6
7. McKey et al. (1978): Compared diets of Colobus satanas monkeys in white sand forests of the Douala- Edea Reserve in Cameroon with diets of Colobus badius & C. guereza monkeys feeding in forests on richer soils in Uganda (Table 10-3). In Cameroon: Monkeys ate 37% leaves, 53% seeds In Uganda: Monkeys ate 75% leaves 10x more monkeys BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 7
8. Resource Availability Theory: Fig. 4-13 - relationship between inherent growth rate and defense investment low investment in mobile defenses by rapidly growing species and high investment in immobile defenses by slow-growing species. BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 8
9. Resource Availability Theory: Fig. 4-14. Costs of mobile vs immobile defenses and changing pattern of defense in young vs old leaves. BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 9
10. Resource Availability Theory: Fig. 5: From Doyle McKey (1984)* - same model as proposed by Coley et al., in their Fig. 4-14. Except that ants are the mobile defense (attracted by foliar nectaries and swollen internodes). *Interaction of the ant-plant Leonarda africana (Caesalpinaceae) with its obligate inhabitants in a rainforest in Cameroon. Biotropica 16(2): 81-99. BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 10
11. Carbon/Nitrogen Balance Theory: Resource Availability Theory predicts that the kind of nutrients available determine whether defenses are carbon-based or nitrogen-based. Plants growing on nitrogen-poor soils will use carbon-based toxins such as terpenoids as mobile defenses, while those growing on fertile soils are more likely to use nitrogen-based toxins such as alkaloids or cyanogens as mobile defenses. Slow-growing plants living under low light availability on poor soils have long-lived leaves that are most economically defended with immobile polymers such as carbon-based tannins and lignins. Current theory is based on Bryant, Chapin & Klein (1983) - see next lecture. BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 11
12. Differences among the ideas - apparency vs resource availability: Is Resource Availability Theory simply Apparency Theory put into an ecosystem context? Resource availability emphasizes the plant perspective. While apparency theory emphasizes the herbivore perspective. BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 12
13. Summary of plant characteristics according to Resource Availability Theory (Table 4-7). BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 13
14. Are generalists important? Freeland, W.J., and D.H. Janzen (1974). Strategies in herbivory by mammals: The role of plant secondary compounds. The American Naturalist 108: 269-289. Study of the effects of such chemical diversity on herbivores has been confined largely to animals small enough to spend their life, or an important developmental stage, on an individual plant or plant population. Here we explore some effects of plant secondary compounds on feeding traits of animals that normally take food from many plants and plant populations during their lifetime. They considered mammals - but could include bird herbivores, lizards, fish, and generalist insects such as leaf-cutter ants and some orthopterans BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 14
15. Summary from Freeland and Janzen Herbivores are capable of detoxifying and eliminating secondary compounds. Limitations of these mechanisms force mammalian herbivores to consume a variety of plant foods at any one time, to treat new foods with caution, to ingest small amounts on the first encounter, and to sample food continuously. Selection of foods is based on learning in response to adverse internal physiological effects BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 15
16. The 1981 synthesis by Laurel Fox: Fox, L.R. (1981) Defense and dynamics in plantherbivore systems. American Zoologist 21: 853-864. She contrasts 2 approaches to plant -herbivore interactions: (1) Older applied approach concentrated on population dynamics of consumer species and used classical predation theory to describe herbivore population dynamics and largely ignored plants. (2) Newer approach ignored dynamics of consumers and focused on individual plants and that plants are special types of prey. Emphasis on chemical and structural properties of individual plants that affect their resistance to herbivores. BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 16
17. Fox (1981): Reviewed the newer approach and compared Feeny's apparency theory with Rhoades & Cates optimal defense theory. Major points are: Often poor distinctions between toxins and digestibility reducers. Unapparent plants are more likely to generate stepwise coevolutionary patterns with specialized herbivores, But apparent plants are more likely to coevolve diffusely with larger numbers of generalist herbivores. BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 17
18. Table 1 from Fox (1981): BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 18
19. Table 2 from Fox (1981) with her idea of coevolution between plants and herbivores for unapparent vs apparent plants. BIOS 5970: Plant-Herbivore Interactions - Dr. S. Malcolm. Week 5: Plant defense theory 2: Development Slide - 19