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Community Ecology

Community Ecology. 10/27/06. Review of last time: Multiple Choice S. Which of the following are true of the following equations:. Circle ALL correct answers: The equations could describe competition between the two species. The equations could describe a predator-prey relationship.

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Community Ecology

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  1. Community Ecology 10/27/06

  2. Review of last time: Multiple ChoiceS Which of the following are true of the following equations: Circle ALL correct answers: • The equations could describe competition between the two species. • The equations could describe a predator-prey relationship. • Interspecific competition dominates intraspecific competition for species F. • When the population S is at zero, and population F is close to zero, the model predicts that population F will grow exponentially

  3. Predator-Prey Relationships • Bottom-up vs. Top-Down control • Predators can promote diversity by • keeping competition in check

  4. Mutualism • Both species benefit

  5. dN1 dt dN2 dt Mutualism • If it is a mutually beneficial relationship, then the two populations increase each other’s size • Population 1  N1 • ti • Population 2  N2 Because this is a positive term, K is increased K1 - N1 + a12 N2 K1 • = r1 * N1 Because this is a positive term, K is increased K2 - N2 + a21 N1 K2 • = r2 * N2

  6. Commensalism • One species benefits, the other is unaffected

  7. dN1 dt dN2 dt Commensalism • If the relationship is commensalistic, one species benefits (the commensal) and the other is unaffected • Population 1  N1 • Population 2  N2 Because this is a positive term, K is increased K1 - N1 + a12 N2 K1 • = r1 * N1 Because there is no a21 term, K is unchanged K2 - N2 K2 • = r2 * N2

  8. How would you model it??? Parasitism

  9. Assumptions of Lotka-Volterra Models • All assumptions of logistic growth model for each species… plus: • Interaction coefficients, carrying capacities, and intrinsic growth rates are constant.

  10. Summary of Interaction Equations: Competition: (- , -) Predator/Prey: (+, -) Mutualism: (+, +) Commensalism: (+, 0)

  11. Test you knowledge! What type of relationship– what equation to use? • A coati eats tree fruit. • Your dog has a flea • You use a fast bicyclist to “draft” off of

  12. Problems with Simple Logistic Growth • Births and deaths not separated -you might want to look at these processes separately -predation may have no effect on birth rate • Carrying capacity is an arbitrary, set value • No age structure

  13. dN dt 1. Separate Births and Deaths = Births - Deaths Births = b*N Deaths = d*N Births and deaths may be density dependent

  14. dN dt 1. Separate Births and Deaths = Births - Deaths Example: Births = b*N(1- N ) K Births = b*N Deaths = d*N Deaths = db+a21N2 Births rate may be density dependent Death rate may be dominated by predator effects

  15. dNH dt NH NP 2. Refine Carrying Capacity If the population is a herbivore, K may depend on the population of plants Kherbivore= Nplant • = rH * NH (1 – )

  16. Remaining Problems • Age Structure • Space: animals rely on different parts of landscape for different parts of their life cycle • Individuality: Populations are collections of individuals, not lumped pools

  17. General Notes on Using Models • How complex should model be? K.I.S.S. • Identify research needs: • Build model structure • Test model to see what it is most sensitive to • Do research to find values of unknown parameters • If build a model that accurately predicts dynamics, it can be used as a management tool. • Look critically at assumptions!

  18. Community Dynamics Community: a group of populations (both plants and animals) that live together in a defined region.

  19. Trophic Cascade Eagles 4th trophic level predator/ tertiary consumer predator/ secondary consumer Foxes 3rd trophic level herbivore/ primary consumer 2nd trophic level Mice autotroph/ primary producer Plants 1st trophic level

  20. How would we Model the Fox Population? Why not include the effect of the plant population? What if foxes had a competitor?

  21. Trophic Cascade Eagles 4th trophic level if eagles go extinct, what could happen to… foxes? mice? plants? Foxes 3rd trophic level 2nd trophic level Mice Plants 1st trophic level

  22. Trophic Cascade Eagles 4th trophic level If a new predator on mice is introduced, what could happen to… mice? plants? foxes? eagles? Foxes 3rd trophic level 2nd trophic level Mice Plants 1st trophic level

  23. Trophic Cascade Eagles 4th trophic level If drought caused a dip in plant production, what would happen to… mice? foxes? eagles? Foxes 3rd trophic level 2nd trophic level Mice Plants 1st trophic level

  24. Simplified Temperate Forest Food WebWhat happens to when it’s a WEB instead of a CHAIN? Eagle Wolf Fox Shrews Deer Caterpillars Rabbit Oak seedling Grasses Herbs In long term, balance is restored

  25. Food Web doesn’t account for Keystone Species

  26. Summary • Modeling Species Interactions • Competition • Predator-prey • Mutualism • Commensalism • Community Dynamics • Food Webs • Keystone Species GOOD LUCK ON MONDAY’S MIDTERM!!! NO BLUE BOOKS OR CALCULATORS NEEDED.

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