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Competition- MBEA Activity


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  • 1. Dr. Mark A. McGinley
    Texas Tech University
    BIOL 5311
    Summer 2011
    Competition:MBEA Activity
  • 2. Competition
    Competition is an ecological interaction in which both participants are harmed.
    Competition can occur between members of the same species
    Intraspecific competition
    Modeled in the logistic growth equation
    Competition can occur between members of different species
    Intraspecific competition
  • 3. Competition
    Competition occurs when resources are limited.
    Soil nutrients
  • 4. Mechanisms of Competition
    There are two mechanisms of competition
    Interference competition
    Exploitative competition
  • 5. Interference Competition
    Two male deer fighting over females
    Interference competition between lion and hyena
  • 6. Exploitative Competition
    Exploitative competition occurs when one individual consumes an resource so it is no longer available for consumption by another individual.
    Exploitative competition is the most common mechanism of competition.
  • 7. Exploitative Competition
    Explotative competition for light in rainforest
    Exploitative competition for berries in cardinals
  • 8. Effects of Intraspecific Competition
    Intraspecific competition can affect
    Population sizes
    Patterns of spatial dispersion
  • 9. Intraspecific Competition
    Intraspecific competition for resources can be an important factor influencing population size
    Modeled by the logistic growth equation
    As N increases b decreases and d increases so r decreases
  • 10. Spatial Dispersion
    Spatial dispersion describes how individuals are located across space
    even , clumped, random
  • 11. Competition and Dispersion
    Competition may lead to even patterns of dispersion
    Individuals that are two close to each other compete and die.
    Common in some desert shrubs
  • 12. Effects of Interspecific Competition
    Interspecific competition may affect
    Population size
  • 13. Studying Competition
    Ecologists have studied competition using theoretical models, observations, and experiments
  • 14. Studying Competition: Observations
    Observational studies can be used to look for evidence of competition
    Negative associations between presence/absence of species
    Negative correlation between abundance of species
  • 15. Studying Competition: Experiments in the Lab
  • 16. Studying Competition: Experiments in the Field
    In the Chihuahuan Desert in Arizona researchers have studied competition between desert rodents and ants by setting up experiments where they experimentally manipulated the population size of one species and observed changes in other species population size in response.
  • 17. Modeling Competition
    Relatively simple to modify the Logistic Growth Model to include the effects of interspecific competition
    The Lotka-Volterra Model of competition examines competition between 2 species
  • 18. Lotka-Volterra Model of Competition
    Can examine the results of this model graphically
  • 19. Results
    Three possible outcomes of competition between two species
    One species wins and drives the other extinct
    Coexistence, unstable
    Coexistence, stable
    The stable coexistence result is the one that we are most interested in
    Two species can coexist only if the strength of intraspecific competition is greater than the strength of interspecifccompetition
  • 20. Competition
    Competitive Exclusion Principle
    If two species share exactly the same niche then they will not be able to coexist
    One species will win and the other will go extinct
    Thus, species can only coexist if the have different niches
    Niches differentiation.
  • 21. Niche
    “The Niches is a bi**c!!”
    There are many different definitions of niche. In this discussion I am talking about “feeding niche” which describes what, when, and where an organism eats.
  • 22. Niche Differentiation
    Organisms can differentiate their niches by
    Eating different foods
    E.g., insects and seeds
    Feeding in different places
    E.g., feeding on seeds found under desert shrubs or in the open
    E.g., feeding on bugs on the top or bottom of trees
    Feeding at different times
    E.g., feeding on insects that are active during the day versus those that are active at night.
  • 23. Niche Differentiation
    Often feeding niches is influenced by the size
    Either of organisms
    Trophic structures (the structures used to capture food)
    Animals with the same sized trophic structures often eat the same food
    Therefore two organisms of the same size might compete too much to be able to coexist
  • 24. Law of Limiting Similarity
    There is a limit to how similar two niches can be in order to allow two species to coexist.
  • 25. Niche Differentiation
    Therefore species that are of similar sizes may not be able to coexist.
    If two species compete because their niches overlap then natural selection might cause their niches to vary so that they no longer overlap
    Character Displacement
  • 26. Character Displacement
  • 27. Character Displacement in Darwin’s Finches
  • 28. Insectivorous Bats
    Most of the bats captures in Krau Wildlife Reserve are insectivores (the rest are frugivores and nectarivores)
    Insectivorous bats use their echolocation system to locate flying insects and they capture their prey in flight.
  • 29. Insectivorous Bats
    Insectivorous bats can reduce competition by
    Feeding on different sizes of insects
    Size of insects that bats can eat appears to be correlated with their size
    Bigger bats can eat bigger bugs
    Feeding in different parts of the forest
    E.g., feed in in the open spaces above the forest versus feeding in the canopy
  • 30. Current Research
    Ongoing research conducted by Dr. Kingston, her graduate students Julie Sewani and AinNural, and colleagues from Germany examines-
    Diet of the bats
    Examine fecal samples
    Relationship between morphology and diet
    Effect of jaw size on bite force
    Effects of morphology on foraging ability
    Relationship between size and diet
    Relationship between wing shape and diet
    Relationship between morphology and foraging location
    E.g., how close to objects can bats catch a prey?
  • 31. Strength of Competition
    Because a bat’s feeding strategy influenced by body size, wing shape, and echolocation system we expect members of the same species to compete most strongly (they are all similar in size).
    Because of similarities of members of the same genus we would expect that members of the same genus should compete more strongly than members of different genera.
  • 32. Activity 1
    Question: Do members of the same genus compete for resources?
    If members of two species are competing for resources then we predict
    Negative association between the presence of both species in a sample
    Negative correlation between the abundance of the two species
  • 33. Genus Rhinolophus
    R. stheno R. lepidus
  • 34. Activity #1
    Use the data from 2009 MBEA to
    1. test for an association between the presence of R. sthenoand the presence of R. lepidusin a sample
    2. test for a correlation between the abundance of R. sthenoand R. lepidusin a sample
  • 35. Results
  • 36. Niche Differentiation
    Because there was no indication of a negative association between the presence/absence of the two species or a negative correlation between the abundance of the two species it appears that the species are not competing strongly for resources.
    Is there evidence for niche differentiation between these two species?
    Assume that diet is influenced by body size
    Is there overlap in body size between the two species.?
  • 37. Activity 2
    Draw the frequency distribution for body size (you can use either mass or forearm length) for both species
    Do we see niche overlap or niche differentiation?
  • 38. Activity 3
    Use the correct statistical test to test for difference between the mean size of the two species.