VI. COMPETITION
d. Problems with L-V Models
- need to do a competition experiment first, to measure α’s, to predict
outcomes of other competition experiments
- don’t know anything about the nature of the competitive interaction… what
are they competing for?
INTERACTIONS AMONG POPULATIONS
VI. COMPETITION
A. Empirical Tests of Competition
B. Modeling): Competition
1. Intraspecific competition
2. Lotka-Volterra Models
3. Tilman Models (1982)
3.Tilman's Resource Models (1982)
):
Isoclines graph population
growth relative to resource ratios
(2 resources, R1, R2)
Consumption rate of Species
A(Ca).
3. Tilman's Resource Models (1982)
Isoclines graph population
growth relative to resource ratios
): R1, R2)
(2 resources,
Consumption rate of Species
A(Ca).
Resource limitation can occur in
different environments with
different initial resource
concentrations (S1, S2).
So, in S2, the population
becomes limited by the short
supply of R2.
Species B requires more of both
resources than species A.
Species B requires more of both
resources than species A. So, no
matter the environment and no
matter the consumptions curves
(lines from S), the isocline for
species B will be "hit" first. So,
Species B will stop growing, but
Species A can continue to grow and
use up resources.... this drops
resources below B's isocline, and B
will decline.
Species B requires more of both
resources than species A. So, no
matter the environment and no
matter the consumptions curves
(lines from S), the isocline for
species B will be "hit" first. So,
Species B will stop growing, but
Species A can continue to grow and
use up resources.... this drops
resources below B's isocline, and B
will decline. So, if one isocline is
completely within the other, then
one species will always win.
If the isoclines intersect, coexistence
is possible (there are densities where
both species are equilibrating at
values > 1).
If the isoclines intersect, coexistence
is possible (there are densities where
both species are equilibrating at
values > 1). Whether this is a stable
coexistence or not depends on the
consumption curves. Consider
Species B. It requires more of
resource 1, but less of resource 2,
than species A. Yet, it also consumes
more of resource 1 than resource 2 - it
is a "steep" consumption curve. So,
species B will limit its own growth
more than it will limit species A.
If the isoclines intersect, coexistence
is possible (there are densities where
both species are equilibrating at
values > 1). Whether this is a stable
coexistence or not depends on the
consumption curves. Consider
Species B. It requires more of
resource 1, but less of resource 2,
than species A. Yet, it also consumes
more of resource 1 than resource 2 - it
is a "steep" consumption curve. So,
species B will limit its own growth
more than it will limit species A. This
will be a stable coexistence for
environments with initial conditions
between the consumption curves (S3).
If the consumption curves were
reversed, there would be an unstable
coexistence in this region.
3. Tilman's Resource Models (1982)
- Benefits:
1. The competition for resources is defined
3. Tilman's Resource Models (1982)
- Benefits:
1. The competition for resources is defined
2. The model has been tested in plants and plankton and confirmed
3. Tilman's Resource Models (1982)
- Benefits:
1. The competition for resources is defined
2. The model has been tested in plankton and confirmed
Cyclotella wins
Cyclotella
Stable Coexistence
PO4 (uM)
Asterionella wins
Asterionella
SiO2 (uM)
3. Tilman's Resource Models (1982)
- Benefits:
1. The competition for resources is defined
2. The model has been tested in plants and plankton and confirmed
3. Also explains an unusual pattern called the "paradox of enrichment"
3. Tilman's Resource Models (1982)
- Benefits:
1. The competition for resources is defined
2. The model has been tested in plants and plankton and confirmed
3. Also explains an unusual pattern called the "paradox of enrichment"
If you add nutrients, sometimes the diversity in a system drops... and one
species comes to dominate. (Fertilize your lawn so that grasses will dominate...
huh?)
If you add nutrients, sometimes the diversity in a system drops... and one
species comes to dominate. Change from an initial stable coexistence scenario (S1)
to a scenario where species A dominates (S2).
3. The Nature of Competitive Interactions
1. Types:
- contest vs. scramble
):
Contest (interference):
Competition for access to resource
Allelopathy/territoriality
Intrasexual selection
Scramble (exploitative):
Direct consumption of resource
Feeding frenzies
3. The Nature of Competitive Interactions
1. Types:
- contest vs. scramble
- symmetrical vs. asymmetrical
- unusual that both competitors are equal across all habitats.
3. The Nature of Competitive Interactions
1. Types:
- contest vs. scramble
- symmetrical vs. asymmetrical
2. Competitive Outcomes:
- Reduction in organism growth and/or pop. size (G, M, R)
- Competitive exclusion (N = 0)
- Reduce range of resources used = resource partitioning.
- If this selective pressure continues, it may result in a
morphological change in the competition. This adaptive response to
competition is called Character Displacement
Character Displacement