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Population Ecology
I. Attributes
II.Distribution
III. Population Growth – changes in size through time
IV. Species Interactions
V. Dynamics of Consumer-Resource Interactions
VI. Competition
VI. COMPETITION
A. Empirical Tests of Competition
1. Gause
P. aurelia vs. P. caudatum
P. aurelia outcompetes P. caudatum.
VI. COMPETITION
A. Empirical Tests of Competition
1. Gause
):
P. aurelia
vs. P. bursaria
VI. COMPETITION
A. Empirical Tests of Competition
1. Gause
):
P. aurelia
vs. P. bursaria: coexistence
VI. COMPETITION
A. Empirical Tests of Competition
•Competition between two species
of flour beetle: Tribolium
castaneum and T. confusum.
1. Gause
):
2. Park
Tribolium castaneum
TEMP
HUM
T. casteum
won (%)
T. confusum
won (%)
COOL
dry
0.0
100.0
COOL
moist
29.0
71.0
WARM
dry
13.0
87.0
WARM
moist
86.0
14.0
HOT
dry
10.0
90.0
HOT
moist
100.0
0.0
VI. COMPETITION
A. Empirical Tests of Competition
1. Gause
):
2. Park
HUM
T. casteum
won (%)
T. confusum
won (%)
dry
0.0
100.0
moist
29.0
71.0
WARM
dry
13.0
87.0
WARM
moist
86.0
14.0
HOT
dry
10.0
90.0
HOT
moist
100.0
0.0
TEMP
Competitive outcomes
COOL
are dependent on
complex environmental COOL
conditions
Basically, T. confusum wins when it's dry, regardless of temp.
VI. COMPETITION
A. Empirical Tests of Competition
1. Gause
):
2. Park
HUM
T. casteum
won (%)
T. confusum
won (%)
dry
0.0
100.0
moist
29.0
71.0
WARM
dry
13.0
87.0
WARM
moist
86.0
14.0
HOT
dry
10.0
90.0
HOT
moist
100.0
0.0
TEMP
Competitive outcomes
COOL
are dependent on
complex environmental COOL
conditions
But when it's moist, outcome depends on temperature
VI. COMPETITION
A. Empirical Tests of Competition
1. Gause
):
2. Park
3. Connell
Intertidal organisms show a zonation
pattern... those that can tolerate more
desiccation occur higher in the
intertidal.
3. Connell - reciprocal transplant experiments
Fundamental Niches defined by physiological tolerances
increasing desiccation stress
):
3. Connell - reciprocal transplant experiments
Realized Niches defined by competition
):
Balanus competitively
excludes Chthamalus
from the "best" habitat,
and limits it to more
stressful habitat
VI. COMPETITION
B. Modeling Competition
1. Intraspecific competition
VI. COMPETITION
B. Modeling Competition
2. Interspecific competition
The effect of 10 individuals
of species 2 on species 1, in
terms of 1, requires a
"conversion term" called a
competition coefficient (α).
VI. COMPETITION
B. Modeling Competition
2. Interspecific competition
We can create an "isocline" that
described the effect of species 2 on
the abundance of species 1 across
all abundances of species 2. For
example, as we just showed, 10
individuals of species 2 reduces
species 1 by 20 individuals, so
species 1 will equilibrate at N1 = 60.
VI. COMPETITION
B. Modeling Competition
2. Interspecific competition
and when N2 = 20 (exerting
a competitive effect equal to
40 N1 individuals), then N1
will equilibrate at N1 = 40.
VI. COMPETITION
B. Modeling Competition
2. Interspecific competition
And, when species 2 reaches an
abundance of 40 (N2 = K1/α12) it
drives species 1 from the
environment (competitive exclusion).
In this case, species 1 equilibrates at
N1 = 0.
So, this line describes the density at
which N1 will equilibrate given a
particular number of N2 competitors
in the environment. This is the
isocline describing dN/dt = 0.
VI. COMPETITION
B. Modeling Competition
2. Interspecific competition
Generalized isocline for
species 1.
VI. COMPETITION
B. Modeling Competition
2. Interspecific competition
And for two competing species, describing their effects on one
another.
VI. COMPETITION
B. Modeling Competition
2. Interspecific competition
Now, if we put these isocline together, we can describe the possible
outcomes of pairwise competition.
If the isoclines align like this,
then species 1 always
wins.We hit species 2's
isocline first, and then as
abundances increase, species
2 must decline while species 1
can continue to increase.
Eventually, species 2 will be
driven to extinction and
species 1 will increase to its
carrying capacity.
VI. COMPETITION
B. Modeling Competition
2. Interspecific competition
Now, if we put these isocline together, we can describe the possible
outcomes of pairwise competition.
If the isoclines align like this,
then species 2 always wins.
We hit species 1's isocline
first, and then as abundances
increase, species 1 must
decline while species 1 can
continue to increase.
Eventually, species 1 will be
driven to extinction and
species 2 will increase to its
carrying capacity.
VI. COMPETITION
B. Modeling Competition
2. Interspecific competition
Now, if we put these isocline together, we can describe the possible
outcomes of pairwise competition.
The effects are more interesting if
the isoclines cross. There is now
a point of intersection, where
BOTH populations have a nonzero equilibrium. This is
competitive coexistence. And it is
stable - a departure from this point
drives the dynamics back to this
point. Essentially, each species
reaches it's own carrying capacity
before it can reach a density at
which it would exclude the other
species.
VI. COMPETITION
B. Modeling Competition
2. Interspecific competition
Now, if we put these isocline together, we can describe the possible
outcomes of pairwise competition.
Here the isocline cross, too. But
each species reaches a density at
which it would exclude the other
species before it reaches its own
carrying capacity. So, although an
equilibrium is possible
(intersection), it is unstable... any
deviation will result in the
eventual exclusion of one species
or the other.