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Competition

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Competition Individual Interactions, part 1 Disruptive selection Niche A concept that encompasses all of the individual environmental requirements of a species This ... – PowerPoint PPT presentation

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Title: Competition


1
Competition
  • Individual Interactions, part 1

2
Niche
  • A concept that encompasses all of the individual
    environmental requirements of a species
  • This is definitely an abstract concept, but it
    helps us to organize and explain ecological
    phenomena

3
What are some possible elements of this
organisms niche?
4
Niche
  • A species niche is composed of both physical
    (e.g., average temperature) and biotic (e.g.,
    food sources) components
  • Resources comprise a critical subset of these
    niche elements

5
Resources
  • Include such things as
  • Food or nutrients
  • Shelter
  • Space to grow
  • Water
  • Light (plants)

6
Resources
  • Resources are usually limited
  • Individuals compete for limited resources

7
Competition
  • Competition can be separated into two broad
    categories of interactions
  • Interference Competition direct antagonistic
    behavior towards other individuals (e.g.,
    defending territory)
  • Resource Competition individuals compete
    indirectly through the exploitation of a shared
    resource

8
Competition
  • Competition for resources between individuals of
    the same species Intraspecific competition

9
Intraspecific Competition
  • Leads to the process of self-thinning in plants

10
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11
Intraspecific Competition
  • Intraspecific competition regulates population
    growth in a density-dependent manner
  • as individuals deplete resources, population
    growth slows until the population size K

K
dN/dt rmaxN(K-N/K)
12
Intraspecific Competition
  • When genetic factors influence the efficiency of
    resource use, evolution tends to increase the
    competitive ability within a population

Resource availability
K1
K2
Population density
13
Competition
  • Competition for resources between individuals of
    different species Interspecific competition

14
Interspecific Competition
  • Played a prominent role in Darwins theory of
    natural selection
  • struggle for existence based on competition for
    limited resources
  • Competition should be most intense between
    closely related species

15
Modeling Interspecific Competition
Lotka-Volterra Model
Population growth of species 1 dN1/dt
rmax1N1(K1-N1/K1)
Population growth of species 2 dN2/dt
rmax2N2(K2-N2/K2)
We can modify these logistic growth equations to
account for interspecific competition by adding
competition coefficients
-?12N2
-?21N1
and
16
Modeling Interspecific Competition
Lotka-Volterra Model
Population growth of species 1 dN1/dt
rmax1N1(K1-N1-?12N2/K1)
Population growth of species 2 dN2/dt
rmax2N2(K2-N2-?21N1/K2)
17
Modeling Interspecific Competition
Lotka-Volterra Model
When population growth has stopped
dN1/dt rmax1N1(K1-N1-?12N2/K1) 0
dN2/dt rmax2N2(K2-N2-?21N1/K2) 0
This can be rearranged algebraically
18
Modeling Interspecific Competition
Lotka-Volterra Model
To predict when population growth in each species
will stop
N1 K1-?12N2
and
N2 K2-?21N1
19
Modeling Interspecific Competition
Lotka-Volterra Model
20
Modeling Interspecific Competition
Lotka-Volterra Model
Species can only coexist when
K1gt K2/?21
K2gt K1/?12
and
that is, when intraspecific competition is
greater than interspecific competition
21
Interspecific Competition
  • G.F. Gause (1934) integrated the idea of the
    niche and interspecific competition
  • Competitive Exclusion Principle
  • Two species with identical niches cannot coexist
    indefinitely (one will out-compete the other for
    limited resources)

22
K of P. aurelia alone 195
K of P. caudatum alone 137
23
Competitive Exclusion
  • Grown separately, P. aurelia had a higher K than
    P. caudatum
  • Grown together, P. aurelia out-competed P.
    caudatum for resources (growth medium), and P.
    caudatum was eliminated

24
Interspecific competition the niche
  • Hutchinson fundamental niche defines the
    environmental conditions in which a species might
    live, in the absence of interactions with other
    species realized niche is the actual niche of a
    species, which is limited by biotic interactions
    (competition, predation, etc.)

25
Interspecific competition - Gallium
G. saxatile
G. pumilum
A. Tansley (1917)
26
Interspecific competition
27
Interspecific competition - Gallium
On limestone (basic) soils, G. pumilum overgrew
and eliminated G. saxatile by the end of the
first growing season
On acidic soils, G. saxatile was completely
dominant, but G. pumilum was not completely
eliminated by the 6th year. Growth of both
species was much slower on the acidic soils.
A. Tansley (1917)
28
Interspecific competition - Gallium
  • The fundamental niches of both Gallium species
    include a wider variety of habitats (soil types)
    than those they actually inhabit in nature
  • Interspecific competition restricts the realized
    niche of each species to a narrower range of soil
    types
  • Asymmetric competition each species is able to
    specialize in its realized niche because each is
    better at doing a different thing (e.g.,
    exploiting resources vs. tolerating stress)

29
Interspecific competition - Gallium
  • Asymmetric competition each species is able to
    specialize in its realized niche because each is
    better at doing a different thing (e.g.,
    exploiting resources vs. tolerating stress)

30
Interspecific competition - barnacles
Joseph Connell (1961)
31
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32
REVIEW QUESTION
  • What type of selection pattern (stabilizing,
    directional, disruptive) would you expect to
    observe in a population undergoing intense
    intraspecific competition for resources?

33
REVIEW QUESTION
  • How might the realized niches of two competing
    species evolve?

34
Disruptive selection
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