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Competition- MBEA Activity
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Competition- MBEA Activity






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    Competition- MBEA Activity Competition- MBEA Activity Presentation Transcript

    • Dr. Mark A. McGinley
      Texas Tech University
      BIOL 5311
      Summer 2011
      Competition:MBEA Activity
    • 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
    • Competition
      Competition occurs when resources are limited.
      Soil nutrients
    • Mechanisms of Competition
      There are two mechanisms of competition
      Interference competition
      Exploitative competition
    • Interference Competition
      Two male deer fighting over females
      Interference competition between lion and hyena
    • 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.
    • Exploitative Competition
      Explotative competition for light in rainforest
      Exploitative competition for berries in cardinals
    • Effects of Intraspecific Competition
      Intraspecific competition can affect
      Population sizes
      Patterns of spatial dispersion
    • 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
    • Spatial Dispersion
      Spatial dispersion describes how individuals are located across space
      even , clumped, random
    • 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
    • Effects of Interspecific Competition
      Interspecific competition may affect
      Population size
    • Studying Competition
      Ecologists have studied competition using theoretical models, observations, and experiments
    • 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
    • Studying Competition: Experiments in the Lab
    • 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.
    • 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
    • Lotka-Volterra Model of Competition
      Can examine the results of this model graphically
    • 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
    • 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.
    • 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.
    • 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.
    • 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
    • Law of Limiting Similarity
      There is a limit to how similar two niches can be in order to allow two species to coexist.
    • 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
    • Character Displacement
    • Character Displacement in Darwin’s Finches
    • 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.
    • 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
    • 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?
    • 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.
    • 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
    • Genus Rhinolophus
      R. stheno R. lepidus
    • 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
    • Results
    • 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.?
    • 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?
    • Activity 3
      Use the correct statistical test to test for difference between the mean size of the two species.