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Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
A. Additive Competitive Effects
. Vandermeer 1969
Dynamics in 4-species
protist communities of
Blepharisma, P caudatum,
P.aurelia, and P. bursaria
were consistent with
predictions from 2species L-V interactions.
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
A. Additive Competitive Effects
B. Non-Additive Competitive Effects
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
A. Additive Competitive Effects
B. Non-Additive Competitive Effects
so, the addition of a third species changes the effect of one
species on another .... which is defined as α12N2.
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
A. Additive Competitive Effects
B. Non-Additive Competitive Effects
so, the addition of a third species changes the effect of one
species on another .... which is defined as α12N2.
Well, that means the third species can influence the competitive
effect by changing either component (α12) or (N2).
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
A. Additive Competitive Effects
B. Non-Additive Competitive Effects
1. Indirect Effects - mediated through changes in abundance
Worthen and Moore (1991)
Indirect, non-additive competitive effects. D. falleni and D.
tripunctata each exert negative competitive effects on D. putrida in
pairwise contests, but D. putrida does better with BOTH competitors
present than with either alone
NON-ADDITIVE
ADDITIVE
Worthen and Moore (1991)
Indirect, non-additive competitive effects. D. falleni and D.
tripunctata each exert negative competitive effects on D. putrida in
pairwise contests, but D. putrida does better with BOTH competitors
present than with either alone
D. tripunctata
D. falleni
D. putrida
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
A. Additive Competitive Effects
B. Non-Additive Competitive Effects
1. Indirect Effects - mediated through changes in abundance
2. Higher Order Interactions - mediated through changes in
the competitive interaction (coefficient), itself; not abundance
consider 2 species, and the effect of N2 on N1 as aN2.
N1
N2
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
A. Additive Competitive Effects
B. Non-Additive Competitive Effects
1. Indirect Effects - mediated through changes in abundance
2. Higher Order Interactions - mediated through changes in
the competitive interaction (coefficient), itself; not abundance
N1 N3 N2
Now, suppose we add species 3
HERE, as shown...
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
A. Additive Competitive Effects
B. Non-Additive Competitive Effects
1. Indirect Effects - mediated through changes in abundance
2. Higher Order Interactions - mediated through changes in
the competitive interaction (coefficient), itself; not abundance
N1 N3 N2
So NOW, N2 may shift AWAY from N1,
reducing its competitive effect.
2. Higher Order Interactions - Wilbur 1972
Ambystoma tremblay
Ambystoma laterale
Ambystoma maculatum
Mean mass of 32 A. laterale
32 A. laterale alone = 0.940 g
0.686 g
0.608 g
0.589 g
w/ 32 A. tremblay
w/ 32 A. maculatum
w/both
Abundances are constant, so the non-additive effect must
be by changing the nature of the interaction
2. Higher Order Interactions - Wilbur 1972
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
A. Additive Competitive Effects
B. Non-Additive Competitive Effects
1. Indirect Effects - mediated through changes in abundance
2. Higher Order Interactions - mediated through changes in
the competitive interaction (coefficient), itself; not abundance
3. Mechanisms:
Change size of organisms and affect their competitive pressure
Change activity level and affect their resource use
Change behavior... and resource use
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
A. Additive Competitive Effects
B. Non-Additive Competitive Effects
C. Results
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
A. Additive Competitive Effects
B. Non-Additive Competitive Effects
C. Results
1. Niche Partitioning at the Community Level: Species Packing
There should be a non-random ordering of species along some resource
axis or associated morphological axis. This can be tested through nearest
neighbor analyses. What would you see if they were ordered randomly?
Then compare.
Worthen and Jones (2006, 2007)
100
Mean Perch Height (cm)
Celithemis elisa
80
Celithemis verna
Celithemis fasciata
Erythemis simplicicollis
60
Libellula auripennis
Libellula cyanea
Libellula incesta
40
Libellula luctuosa
Pachydiplax longipennis
Perithemis tenera
20
Plathemis lydia
0
0
100
200
300
Mean Mass (mg)
400
500
Worthen (2009)
140
Mean Perch Height (cm)
120
Williams (1994) V-test, v = 0.007, p < 0.05
100
80
60
40
20
0
1
2
3
4
Amberwing
Pondhawk
Blue Dasher
Goldenwing
5
Slaty
6
Saddlebags
1. Niche Partitioning at the Community Level: Species Packing
Dayan et al., 1989. Species packing in weasels in Israel.
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
A. Additive Competitive Effects
B. Non-Additive Competitive Effects
C. Results
1. Niche Partitioning in Communities: Species Packing
2. Optimal Size
2. Optimal Size
% of Species
For most groups of animals there is a 'right skew' to the frequency
distribution of species ordered by size (log scale)
SIZE
2. Optimal Size
For most groups of animals there is a 'right skew' to the frequency
distribution of species ordered by size (log scale)
Why? Trade offs in reproductive work (Brown)
- Large animals: lots of energy absorbed, but metabolic
conversion to offspring is slow
SIZE
2. Optimal Size
For most groups of animals, there is a 'right skew' to the frequency
distribution of species ordered by size (log scale)
Why? Trade offs in reproductive work (Brown)
- Large animals: lots of energy absorbed, but metabolic
conversion to offspring is slow
- Small animals: good efficiency, but limited by energy they
can collect
SIZE
2. Optimal Size
For most groups of animals, there is a 'right skew' to the frequency
distribution of species ordered by size (log scale)
Why? Trade offs in reproductive work (Brown)
- result: there is a MOST EFFICIENT SIZE for a type of animal
SIZE
2. Optimal Size
For most groups of animals, there is a 'right skew' to the frequency
distribution of species ordered by size (log scale)
Why? Trade offs in reproductive work (Brown, 1993)
- result: there is a MOST EFFICIENT SIZE for a type of animal
2. Optimal Size
For most groups of animals, there is a 'right skew' to the frequency
distribution of species ordered by size (log scale)
Why? Trade offs in reproductive work (Brown)
- result: there is a MOST EFFICIENT SIZE for a type of animal
NOW: Consider multiple species filling up the environment...
- each species will be selected to attain the optimum size
2. Optimal Size
For most groups of animals, there is a 'right skew' to the frequency
distribution of species ordered by size (log scale)
Why? Trade offs in reproductive work (Brown)
- result: there is a MOST EFFICIENT SIZE for a type of animal
NOW: Consider multiple species filling up the environment...
- each species will be selected to attain the optimum size
- but since size is an important correlate to resource use, at
some point a species will do better "off the optimum", rather than
competing with lots of species on the optimum....
NOW: Consider multiple species filling up the environment...
- each species will be selected to attain the optimum size
- but since size is an important correlate to resource use, at
some point a species will do better "off the optimum", rather than
competing with lots of species on the optimum....
NOW: Consider multiple species filling up the environment...
- each species will be selected to attain the optimum size
- but since size is an important correlate to resource use, at
some point a species will do better "off the optimum", rather than
competing with lots of species on the optimum....
NOW: Consider multiple species filling up the environment...
- each species will be selected to attain the optimum size
- but since size is an important correlate to resource use, at
some point a species will do better "off the optimum", rather than
competing with lots of species on the optimum....
NOW: Consider multiple species filling up the environment...
- each species will be selected to attain the optimum size
- but since size is an important correlate to resource use, at
some point a species will do better "off the optimum", rather than
competing with lots of species on the optimum....
NOW: Consider multiple species filling up the environment...
- each species will be selected to attain the optimum size
- but since size is an important correlate to resource use, at
some point a species will do better "off the optimum", rather than
competing with lots of species on the optimum....
NOW: Consider multiple species filling up the environment...
- each species will be selected to attain the optimum size
- but since size is an important correlate to resource use, at
some point a species will do better "off the optimum", rather than
competing with lots of species on the optimum....
NOW: Consider multiple species filling up the environment...
- each species will be selected to attain the optimum size
- but since size is an important correlate to resource use, at
some point a species will do better "off the optimum", rather than
competing with lots of species on the optimum....this is not as great
a size class, so species will move to new size class to avoid
competition more rapidly...
NOW: Consider multiple species filling up the environment...
- each species will be selected to attain the optimum size
- but since size is an important correlate to resource use, at
some point a species will do better "off the optimum", rather than
competing with lots of species on the optimum....this is not as great
a size class, so species will move to new size class to avoid
competition more rapidly...
NOW: Consider multiple species filling up the environment...
- each species will be selected to attain the optimum size
- but since size is an important correlate to resource use, at
some point a species will do better "off the optimum", rather than
competing with lots of species on the optimum....this is not as great
a size class, so species will move to new size class to avoid
competition more rapidly...small size is constrained... but large is
not.....
NOW: Consider multiple species filling up the environment...
- each species will be selected to attain the optimum size
- but since size is an important correlate to resource use, at
some point a species will do better "off the optimum", rather than
competing with lots of species on the optimum....this is not as great
a size class, so species will move to new size class to avoid
competition more rapidly...small size is constrained... but large is
not.....RESULT: RIGHT SKEW
NOW: Consider multiple species filling up the environment...
- each species will be selected to attain the optimum size
- but since size is an important correlate to resource use, at
some point a species will do better "off the optimum", rather than
competing with lots of species on the optimum....this is not as great
a size class, so species will move to new size class to avoid
competition more rapidly...small size is constrained... but large is
not.....RESULT: RIGHT SKEW
Think about the Fretwell-Lucas model of habitat selection... the
optimum is used first, and when this "size niche" is full, less optimal
niches are colonized.
NOW: Consider multiple species filling up the environment...
- each species will be selected to attain the optimum size
- but since size is an important correlate to resource use, at
some point a species will do better "off the optimum", rather than
competing with lots of species on the optimum....this is not as great
a size class, so species will move to new size class to avoid
competition more rapidly...small size is constrained... but large is
not.....RESULT: RIGHT SKEW
Think about the Fretwell-Lucas model of habitat selection... the
optimum is used first, and when this "size niche" is full, less optimal
niches are colonized.
Size correlates with so many patterns of resource use that it is a
good generic proxy for niche use.
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
III. Multispecies Interactions across Trophic Levels
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
III. Multispecies Interactions across Trophic Levels
A. Keystone Predators
A. Keystone Predators
1. Paine (1966) - the rocky intertidal
Arrows show
energy flow; point
to consumer.
A. Keystone Predators
1. Paine (1966) - the rocky intertidal
- Pisaster prefers mussels
A. Keystone Predators
1. Paine (1966) - the rocky intertidal
- Pisaster prefers mussels
- When predators are excluded,
mussels outcompete other species and
the diversity of the system crashes to a
single species - a mussel bed
A. Keystone Predators
1. Paine (1966) - the rocky intertidal
- Pisaster prefers mussels
- When predators are excluded,
mussels outcompete other species and
the diversity of the system crashed to a
single species - a mussel bed
- When predators are present, the
abundance of mussels is reduced, space
is opened up, and other species can
colonize and persist.
A. Keystone Predators
1. Paine (1966) - the rocky intertidal
- Pisaster prefers mussels
- When predators are excluded,
mussels outcompete other species and
the diversity of the system crashed to a
single species - a mussel bed
- When predator is present, the
abundance of mussels is reduced, space
is opened up, and other species can
colonize and persist.
So, although Pisaster does eat the other species (negative effect) it
exerts a bigger indirect positive effect by removing the dominant competitor
A. Keystone Predators
2. Lubchenco (1978)
Littorina littorea feeding on algae
A. Keystone Predators
2. Lubchenco (1978)
- Snails prefer Enteromorpha to Chondrus
- E is dominant in tide pools,
- C is dominant on exposed rock
A. Keystone Predators
2. Lubchenco (1978)
- Snails prefer Enteromorpha to Chondrus
- E is dominant in tide pools,
- C is dominant on exposed rock
In pools, snails are feeding on the dominant and
you get a keystone effect from low to
intermediate snail densities; then they are so
abundant they eat everything.
A. Keystone Predators
2. Lubchenco (1978)
- Snails prefer Enteromorpha to Chondrus
- E is dominant in tide pools,
- C is dominant on exposed rock
In pools, snails are feeding on the dominant and
you get a keystone effect from low to
intermediate snail densities; then they are so
abundant they eat everything.
On rock, snails feed on competitive subordinate
and Enteromorpha is whacked by competition
AND predation, and diversity declines with
increase snail abundance.
A. Keystone Predators
2. Lubchenco (1978)
- Snails prefer Enteromorpha to Chondrus
- E is dominant in tide pools,
- C is dominant on exposed rock
In pools, snails are feeding on the dominant and
you get a keystone effect from low to
intermediate snail densities; then they are so
abundant they eat everything.
On rock, snails feed on competitive subordinate
and Enteromorpha is whacked by competition
AND predation, and diversity declines with
increase snail abundance.
Effects depend on competitive dynamics, feeding
preferences, and densities
A. Keystone Predators
Dr. Peter Morin
3. Morin - 1983
number of predatory salamanders
Community Ecology
A. Keystone Predators
4. Worthen - 1989
Mean Number of Metamorphs
(log10 transformed)
D. tripunctata
2.5
D. putrida
2
D. falleni
1.5
1
0.5
0
Alone
Three species
no predator
Three species
with predator
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
III. Multispecies Interactions across Trophic Levels
A. Keystone Predators
B. Apparent Competition
B. Apparent Competition
- consider 2 prey species consumed by the same predator
PREDATOR
PREY 1
PREY 2
B. Apparent Competition
- consider 2 prey species consumed by the same predator
- suppose prey 2 increases
PREDATOR
PREY 1
PREY 2
B. Apparent Competition
- consider 2 prey species consumed by the same predator
- suppose prey 2 increases
- this provides more food for the predator,
which increases....
PREDATOR
PREY 1
PREY 2
B. Apparent Competition
- consider 2 prey species consumed by the same predator
- suppose prey 2 increases
- this provides more food for the predator,
which increases....
- and the other species experiences
greater predation and declines…
PREDATOR
PREY 1
PREY 2
B. Apparent Competition
- consider 2 prey species consumed by the same predator
- suppose prey 2 increases
- this provides more food for the predator,
which increases....
- and the other species experiences
greater predation...
- so an increase in one prey causes
a decrease in the other... but this
is an indirect effect mediated through
a predator.
PREDATOR
PREY 1
PREY 2
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
III. Multispecies Interactions across Trophic Levels
A. Keystone Predators
B. Apparent Competition
C. Apparent Mutualism
C. Apparent Mutualism
- consider two prey, each eaten by specialized predators
Predator 1
Predator 2
Prey 1
Prey 2
C. Apparent Mutualism
- consider two prey, each eaten by specialized predators
- Predator 1 increases and reduces Prey 1.
Predator 1
Prey 1
Predator 2
Prey 2
C. Apparent Mutualism
- consider two prey, each eaten by specialized predators
- Predator 1 increases and reduces Prey 1.
- Competition between prey is reduced and Prey 2 increases
Predator 1
Prey 1
Predator 2
Prey 2
C. Apparent Mutualism
- consider two prey, each eaten by specialized predators
- Predator 1 increases and reduces Prey 1.
- Competition between prey is reduced and Prey 2 increases
- This provides more food for predator 2, which then increases
Predator 1
Prey 1
Predator 2
Prey 2
C. Apparent Mutualism
- consider two prey, each eaten by specialized predators
- Predator 1 increases and reduces Prey 1.
- Competition between prey is reduced and Prey 2 increases
- This provides more food for predator 2, which then increases
- So, an increase in one predator has had an indirect positive effect on another
predator.
Predator 1
Prey 1
Predator 2
Prey 2
Community Ecology
I. Introduction
II. Multispecies Interactions with a Trophic Level
III. Multispecies Interactions across Trophic Levels
A. Keystone Predators
B. Apparent Competition
C. Apparent Mutualism
D. Intraguild Predation
D. Intraguild Predation
- eat your competitor!
- get a meal and reduce competition!
Wissinger, et al. 1993. Intraguild predation in larval dragonflies
Tramea lacerata
Erythemis simplicicollis
Damselflies - prey
D. Intraguild Predation
- eat your competitor!
- get a meal and reduce competition!
Wissinger, et al. 1993. Intraguild predation in larval dragonflies
significant non-additive effect
What effect will an introduced species have on a community?
What effect will the loss of a species have on a community?
“The first rule of the tinkerer is to save all the pieces” – Aldo Leopold