Lecture 14


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Lecture 14

  1. 1. Lecture 14: Community Interactions Covers Chapter 27
  2. 2. Community • A community’s interacting web of life tends to maintain a balance between resources and the number of individuals consuming them.* • Interacting populations influence each other and act as a type of natural selection* • Coevolution: Two interacting species act as agents of natural selection on each other.*
  3. 3. Ecological niche* • In order to understand community interactions, we must understand the meaning of an ecological niche: an organism’s physical home (habitat) • Although different species share aspects of their niche with others, no 2 species occupy the exact same niche • Each species occupies a niche that encompasses all aspects of its way of life:* – Feeding – Reproduction – Survival – Nesting site – Types of nutrients required to live – Amount of water it needs
  4. 4. Most important community interactions • Competition • Predation • Parasitism • Mutualism • (The first 3 are also density-dependent factors that contribute to environmental resistance)
  5. 5. Competition* • Interactions among individuals who attempt to use the same resource(s) • Adaptations can reduce the overlap of niches and thus reduce competition – Competitive Exclusion principle: if 2 species attempt to occupy the same niche, one will outcompete the other – Resource partitioning: If 2 species occupy very similar niches, each species will actually occupy a smaller niche than if there was only one species
  6. 6. P. aurelia P. caudatum (a) Grown in separate flasks (b) Grown in the same flask Competitive Exclusion Fig. 27-1
  7. 7. Resource Partitioning Fig. 27-2 Blackburnian warbler Black-throated green warbler Cape May warbler Bay-breasted warbler Yellow-rumped warbler
  8. 8. Predation • Predators kill/eat other organisms – Herbivores (animals that eat plants) – Carnivores (animals that eat animals) • Predators usually always less abundant than prey* • Predators can survive on different types of prey depending on availability • Predator-prey interactions can affect evolutionary adaptations* – If prey become harder to catch, predators evolve to become better predators – Predators contribute to overall health of prey population by killing the weakest, slowest, perhaps most sick individuals.
  9. 9. Evolutionary adaptations resulting from predator-prey relationships* • Camoflage: renders animals inconspicuous even in plain sight (Both predators and prey can use camoflage) • Warning coloration: attracts attention of prey, warns them that prey is bad-tasting or poisonous • Mimicry: members of one species have evolved to resemble another (non-poisonous prey resembles a poisonous one: predators think they all are poisonous) • Startle coloration: deters predators by scaring them • Aggressive mimicry: predator resembles harmless animal to lure prey • Chemical warfare: toxins for attack or defense
  10. 10. Camouflage by Blending In Fig. 27-4
  11. 11. Camouflage by Resembling Specific Objects Fig. 27-5c, d
  12. 12. Camouflage Assists Predators Fig. 27-6
  13. 13. Warning Coloration Fig. 27-7
  14. 14. Mimicry Fig. 27-9c, d
  15. 15. Startle Coloration Fig. 27-10
  16. 16. Aggressive Mimicry Fig. 27-6b
  17. 17. Chemical Warfare Fig. 27-12a
  18. 18. You Tube: Camo & Mimicry • By Furious Vegetables
  19. 19. Parasitism* • One organism (parasite) feeds off of another (host) • Sometimes harms or weakens host, sometimes kill them • Host can evolve to acquire immunity against parasite • Affects host population by weakening hosts and making them more susceptible to death from other causes OR by reducing host population (if parasite kills host).
  20. 20. Cordyceps: Attack of the Killer Fungi • BBC Worldwide
  21. 21. Mutualism • Interactions between species in which both parties benefit* • Ex: clownfish/sea anemones (clownfish is protected from prey by hanging out in poisonous sea anemone tentacles, clownfish keep anemones free of parasites and feed on their feces)
  22. 22. Mutualism Fig. 27-13b
  23. 23. Symbiosis & Anemone Fish: Reel Life of the Andaman • You Tube: Bubblevision
  24. 24. How do different species affect the community??
  25. 25. Keystone Species • A species that plays a MAJOR role in determining community structure* • If keystone species removed, entire community changes* • Ex: elephants….eat small trees and bushes. This maintains the grassland and prevents forests from becoming overgrown. Grasslands are source of food for many species. If elephants gone, forests would become overgrown and species who live on grasslands would be endangered
  26. 26. How are communities formed?
  27. 27. Succession* • Communities do not emerge fully formed, they arise through succession: community and non-living environment change structurally over time • Succession is preceded by a DISTURBANCE: event that disrupts the ecosystem
  28. 28. Succession • Begins with arrival of a few hardy plants (pioneers) • Competing plants evolve and displace pioneers • Most communities go through stages to become a stable and diverse climax community* • Climax community can sustain itself (unless a disturbance occurs)*
  29. 29. Primary Succession • Community starts “from scratch”, no trace of a previous community* • Can take thousands or tens of thousands of years • Ex: Glacier scours landscape down to bare rock, volcano wipes out all animals and vegetation in a certain area
  30. 30. rock scraped bare by a glacier lichens and moss on bare rock bluebell, yarrow blueberry, juniper jack pine, black spruce, aspen spruce-fir climax forest: white spruce, balsam fir, paper birch 0 1,000 time (years) Primary Succession Fig. 27-16
  31. 31. Secondary Succession • Occurs after a disturbance changes, BUT DOES NOT WIPE OUT, an existing community* • Soil, seeds, some animals may remain after the disturbance. • Ex: Fire
  32. 32. plowed field ragweed, crabgrass, Johnson grass aster, goldenrod, Queen Anne's lace, broom sedge grass blackberry, smooth sumac Virginia pine, eastern red cedar oak-hickory climax forest: white and black oak, bitternut and shagbark hickory 0 100 time (years) Secondary Succession Fig. 27-17