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Population Ecology
Populations are groups of potentially reproducing
individuals in the same place, at the same time, that
share a common gene pool.
I. Spatial Distributions
A. Dispersion
I. Spatial Distributions
A. Dispersion
- Regular
I. Spatial Distributions
A. Dispersion
- Regular
- intraspecific competition
- allelopathy
- territoriality
I. Spatial Distributions
A. Dispersion
- Clumped
- patchy resource
- social effects
I. Spatial Distributions
A. Dispersion
- Random
- canopy trees, later in
succession
I. Spatial Distributions
A. Dispersion
- Complexities
- can change with development. Seedlings
are often clumped (around parent or in a
gap), but randomness develops as
correlations among resources decline.
regular can develop if competition
becomes limiting.
I. Spatial Distributions
A. Dispersion
- Complexities
- can change with development. Seedlings
are often clumped (around parent or in a
gap), but randomness develops as
correlations among resources decline.
regular can develop if competition
becomes limiting.
- can change with population, depending
on resource distribution.
I. Spatial Distributions
A. Dispersion
- Complexities
- can change with development. Seedlings
are often clumped (around parent or in a
gap), but randomness develops as
correlations among resources decline.
regular can develop if competition
becomes limiting.
- can change with population, depending
on resource distribution.
- varies with scale. As scale increases, the
environment will appear more 'patchy' and
individuals will look clumped.
Species Interactions
Effect on Species 2
Positive
Neutral
Negative
Positive
mutualism
commensal
consumer
Neutral
commensal
-
amensal
Negative
consumer
amensal
competition
Effect on species 1
II. COMPETITION
B. Modeling Competition
1. Intraspecific competition
II. 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).
II. COMPETITION
A. Modeling Competition
B. Empirical Tests of Competition
B. Empirical Tests of Competition
1. Gauss
P. aurelia vs. P. caudatum
P. aurelia outcompetes P. caudatum.
B. Empirical Tests of Competition
1. Gauss
P. aurelia vs. P. bursaria
):
B. Empirical Tests of Competition
1. Gauss
P. aurelia vs. P. bursaria: coexistence
):
B. Empirical Tests of Competition
1. Gauss
Why do the outcomes differ?
):
- P. aurelia
and P. caudatum feed on suspended bacteria - they feed
in the same microhabitat on the same things. P. bursaria feeds on bacteria
adhering to the glass of the culture flasks.
B. Empirical Tests of Competition
1. Gauss
Why do the outcomes differ?
):
- P. aurelia
and P. caudatum feed on suspended bacteria - they feed
in the same microhabitat on the same things. P. bursaria feeds on bacteria
adhering to the glass of the culture flasks.
- Gauss concluded that two species using the environment in the
same way (same niche) could not coexist. This is the competitive exclusion
principle.
B. Empirical Tests of Competition
1. Gauss
•Competition between two species
of flour beetle: Tribolium
castaneum and T. confusum.
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
B. Empirical Tests of Competition
1. Gauss
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.
B. Empirical Tests of Competition
1. Gauss
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
B. Empirical Tests of Competition
1. Gauss
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
II. COMPETITION
A. Modeling Competition
B. Empirical Tests of Competition
):
C. 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
III. Predation
A. Predators can limit the growth of prey populations
A. Predators can limit the growth of prey populations
Kelp and Urchins In 1940's:
Kelp and Urchins In 1940's:
Moose and Wolves - Isle Royale
Moose and Wolves - Isle Royale
1930's - Moose population about 2400 on Isle Royale
1930's - Moose population about 2400 on Isle Royale
1949 - Wolves cross on an ice bridge; studied since 1958
1930's - Moose population about 2400 on Isle Royale
1949 - Wolves cross on an ice bridge; studied since 1958
V. Dynamics of Consumer-Resource Interactions
A. Predators can limit the growth of prey populations
B. Oscillations are a Common Pattern
IV. Mutualism
Trophic Mutualisms – help one another get nutrients
Trophic Mutualisms – help one another get nutrients
1-Esophagus
2-Stomach
3-Small Intestine
4-Cecum (large intestine) - F
5-Colon (large intestine)
6-Rectum
Low efficiency - high throughput...
Trophic Mutualisms – help one another get nutrients
Trophic Mutualisms – help one another get nutrients
Trophic Mutualisms – help one another get nutrients
Trophic Mutualisms – help one another get nutrients
Trophic Mutualisms – help one another get nutrients
Trophic Mutualisms – help one another get nutrients
Defensive Mutualisms – Trade protection for food
Defensive Mutualisms – Trade protection for food
Defensive Mutualisms – Trade protection for food
Acacia and Acacia ants
Cleaning Mutualisms – Trade cleaning for food
Dispersive Mutualisms – Trade dispersal for food
Create floral ‘syndromes’ –
suites of characteristics
that predispose use by
one type of disperser
Dispersive Mutualisms – Trade dispersal for food
Dispersive Mutualisms – Trade dispersal for food
Not mutualism
(commensal or
parasitic)
Community Ecology
I. Introduction
A. Definitions of Community
- broad: a group of populations at
the same place and time
“old-hickory community”
Community Ecology
I. Introduction
A. Definitions of Community
- broad: a group of populations at
the same place and time
“old-hickory community”
- narrow: a “guild” is a group of
species that use the same
resources in the same way.
Community Ecology
I. Introduction
A. Definitions of Community
- broad: a group of populations at
the same place and time
“old-hickory community”
-narrow: a “guild” is a group of
species that use the same
resources in the same way.
-complex: communities connected
by migration or energy flow
I. Introduction
A. Definitions
B. Key Descriptors
Species Richness
Species Diversity
Habitat 1
Habitat 2
species A
50
99
species B
50
1
Richness
2
2
Simp. Div.
2
Evenness
Diversity indices
Simpson’s: Σ(pi)2
1.02
C. Conceptual Models
1. Lindeman - 40's - energetic perspective
C. Conceptual Models
1. Lindeman - 40's - energetic perspective
- energetic conversion rates determine biomass transfer:
- endotherm food chains are short; only 10% efficient
C. Conceptual Models
1. Lindeman - 40's - energetic perspective
- energetic conversion rates determine biomass transfer:
- endotherm food chains are short; only 10% efficient
- ectotherm food chains can be longer,
because energy is transfered more
efficiently up a food chain (insects 50% efficient).
C. Conceptual Models
1. Lindeman - 40's - energetic perspective
- energy available in lower level will determine the productivity of
higher levels... this is called "bottom-up" regulation.
not enough energy to support
another trophic level
C. Conceptual Models
1. Lindeman - 40's - energetic perspective
2. Hairston, Slobodkin, and Smith (HSS) - 1960
- Observation: "The world is green" - there is a surplus of vegetation
Hairston, Slobodkin, and Smith (HSS) - 1960
- Observation: "The world is green" - there is a surplus of vegetation
- Implication: Herbivores are NOT limited by food... they must be limited by
something else...predation?
Hairston, Slobodkin, and Smith (HSS) - 1960
- Observation: "The world is green" - there is a surplus of vegetation
- Implication: Herbivores are NOT limited by food... they must be limited by
something else ....predation?
- If herbivore populations are kept low by predators, they must be the
variable limiting predator populations - as food. SO:
Top Pred's: Limited by Competition
Herbivores: Limited by Predation
Plants: Limited by Competition
Hairston, Slobodkin, and Smith (HSS) - 1960
- Observation: "The world is green" - there is a surplus of vegetation
- Implication: Herbivores are NOT limited by food... they must be limited by
predation.
- If herbivore populations are kept low by predators, they must be the
variable limiting predator populations - as food. SO:
Top Pred's: Limited by Competition
Herbivores: Limited by Predation
Plants: Limited by Competition
Community structured by "top-down effects" and trophic cascades
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.
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
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