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Complex cp2011

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  • Mutualism: Within species = co-operationInterspecificegmycorrhizae70% of land plants associated with fungi. Fungi receive sugars made from photosynthesis; plant receives soil nutrients absorbed by fungi.Competition: within and between speciesPredationAmensalism: eg asymmetric competition. Trees and grassesCommensalism: remora feeds off food left over from shark. No effect on shark.
  • The most widespread are the arbuscularmycorrhizas (AM), sometimes called vesicular-arbuscularmycorrhizas. These are found world-wide on many crop plants, wild herbaceous plants and trees, as well as on pteridophytes and some bryophytes. The fungi that form these mycorrhizas are members of the zygomycota, such as Glomus and Acaulospora spp. None of these can be grown in pure culture, away from their host plants. Roots appear quite normal when infected by these fungi, but staining of the root tissues reveals a substantial amount of internal colonisation (Figure 1).
  • Transplant experiment. Grasses grown in soil dominated by different speciesAll did better on soil from other species. Sterlization = diminished this response suggesting it was soil pathogens.
  • Transcript

    • 1.
    • 2. How many species?
      Perhaps 50 million species
      287,655 plants
      74,000–120,000 fungi
      1,250,000 animals:
      1,190,200 invertebrates:
      950,000 insects,
      molluscs, crustaceans, etc.
      58,808 vertebrates:
      29,300 fish,
      5,743 amphibians,
      8,240 reptiles,
      10,234 birds,
      5,146 mammals
    • 3. Why bother?
      Moral/ethical reasons
      Medicine: Antibiotics
      Tropical frogs
      Silk moths, salamanders, snakes, sharks, honeybees
      Ecosystem function
      Higher diversity = higher productivity
    • 4. Speciation & coexistence
      Allopatric speciation
      Sympatric speciation
      Requires coexistence
    • 5. Coexistence in Animals
      Main niche: prey (resource)
    • 6. Gause’s Exclusion principle
      “The struggle for existence” 1934
      Discovered antibiotic used in WWII
      1910-1986
      Two (or more) similar species cannot coexist on a single resource
    • 7. Plants
      Limited range of resources
      Light, water, nutrients
      Rain forest
      Panama 320spp 50ha
      Grassland
      UK, 35spp 1m2
      WHAT PROCESSES MAINTAIN THE DIVERSITY?
    • 8. Interactions
      Mutualism + +
      Competition - -
      Predation/parasitism - +
      Amensalism 0 -
      Commensalism 0 +
      8
    • 9.
    • 10. Arbuscular
      Crop plants
      Herbs, trees
      Roots appear normal
      Staining shows fungi inside the roots structure
      Endo-symbiont
      Clover
      1. Vesicles (storage)
      2. Hyphae
      3. Arbuscules (exchange)
    • 11. Ectomycorrhizas
      Broad leaved trees and conifers
      Pine; spruce; fir; beech; birch
      Most trees in London
      Common mushrooms and toadstools in woodland –fruiting bodies
      No penetration of plant cell
      Form sheath on the root
      Hyphae extend into the soil
    • 12. Root (darker)
      Fungus (white) on root hairs
    • 13. Nitrogen cycle
    • 14. Legumes
      N essential for life
      DNA; RNA; amino acids
      Fixed by many plants
      Symbiosis
      Rhizobia (nodules)
      Legumes release N into soil on death.
      Farmers crop rotation
    • 15. Nitrogen fixing bacteria
    • 16. Nitrogen fixing bacteria
    • 17. Benefits
      Plant
      Improved uptake of soil nutrients
      Ecto: N
      Arb: P
      Immunity to pathogens
      Drought tolerance
      Microbe
      Carbon
    • 18. Possible consequences
      Positive feedback
      Seedlings perform well near to parent
      Nurse plants
      Monodominance?
      Depends on early conditions/densities
      Rain forests
      Species rich
      Large patches >50% of trees of one species
    • 19. Ectomycorrhizal networks
      Larch seedling
      Low nutrient
      (tropics nutrient cycles are faster)
      Soils can be nutrient poor
      Seedlings with access to an ECM network had greater growth
      (73% greater),
      leaf number (55% more), and survivorship (47% greater) than seedlings without such access
    • 20. Early advantage
    • 21. Negative feedbacks
      Build up of soil pathogens
      Seed predators
      Crop rotation
      Janzen-Connell hypothesis
      Negative frequency dependence
      Advantage of rarity
      Coexistence
      Seedling establishment
      Better further away from parent
    • 22. Grassland experiment
      Petermann et al. (2008) Ecology, 89(9): 2399–2406
    • 23. Summary
      Microbes important
      Poor soils
      Early establishment
      Modulate competition?
      Negative feedback
      Temporal variation?
      Stochastic model required
    • 24. Competition
      Lotka-Volterra theory 1920’s
      Tested by Gause in 1930’s
      Coexistence most likely when:
      Intraspecific > interspecific competition
      Niche differentiation
      Coexistence when species most limited by themselves
    • 25. New theory
    • 26. References
      David Read in Nature (November 1998) 396, 22-23; and the full paper on pp. 69-72 in the same issue
      Bever (2003) New Phytologist, 157: 465-473.
      Bever et al. (2010) Trends in Ecology and Evolution, 25: 468-478.