Lecture 12

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Transcript Lecture 12

BIOL 4120: Principles of Ecology
Lecture 12: Interspecfic
competition
Dafeng Hui
Room: Harned Hall 320
Phone: 963-5777
Email: [email protected]
Outline (chapter 13)
13.1 Interspcific competition
13.2 Lotka-Volterra model
13.3 Laboratory experiments support L-V model
13.4 Competitive exclusion principle
13.5 Competition is influenced by nonresource factos
13.6 Temporal variation in environmental factors
13.7 Multiple resources
13.8 Competition change along environmental
gradients
13.9 Niches of species
13.10 Resource partitioning
13.11 Competition influence national selection
13.12 Competition involves biotic and abiotic factors
13.1 Interspecific competition
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A relationship in which the populations of
two or more species are affected
adversely (--)
Seek a common resource in short supply
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Food; Living space; etc
An example: squirrels, mice, deer, various birds
competing for acorns
Model One. Two forms
• Exploitation
• Interference
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Model Two. Six forms
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Consumption
preemption
Overgrowth
Chemical interaction
Territorial
encounter
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Consumption
• Utilization of a shared resource by 2 species
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Preemption
• Occupation of a site by 1st organism stops occupation by 2nd
organism
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Usually sessile organisms
Overgrowth
• Where organism covers another preventing access to a
resource. Trees shade other plants
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Chemical interaction
• Release of toxin to inhibit or kill competing organisms
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Allelopathy in plants
Territorial
• Behavioral exclusion of 1st organism by 2nd organism defending
territory
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Encounter
• Non-territorial encounters cause a negative effect on one or
both species
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Lion and wild dogs over a antelope kill
12.2 Possible outcomes of
Interspecific competition
When two species compete, how many outcomes?
1.
Species 1 wins, species 2 loses
2.
Species 1 loses, species 2 wins
3.
Coexistence (stable equilibrium)
4.
Competition can go wither way (unstable
equilibrium)
These competition results can be described by LotkaVolterra model.
Lokta-Volterra Model
Derived from logistic equation
Add influence of another species (a competition
component)
alpha(2,1)=
alpha
Alpha(1,2)=
beta
Lokta-Volterra Model
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αN2 and βN1: effect of interspecific competition,
namely, where α and β per capita effects of
competition
In term of resource use, an individual of species
2 is equal to α individuals of species 1
No interspecific competition, then α and β are 0 and
normal growth to carrying capacity
Interspecific competition is density dependent
(a) Species 1 alone or no competition
Diagonal line is zero growth isocline
(b) Species 2 alone or no competition
(c) Species 1 inhibits growth of species 2
and latter goes extinct
(d) Species 2 inhibits growth of species 1
and latter goes extinct
(e) Unstable situation, both inhibit in a density
dependent manner. Depending on initial density,
either can make other extinct
(f) Each species inhibits its own population
growth more than competitor. Neither can
eliminate competitor
13.3 Laboratory experiments support the
Lotka-Volterra Equations
Russian biologist G.F. Gause
Competition between two
species
P. aurelia has a high growth
rate and can tolerate a higher
population density
Two Paramecium (unicellular ciliated protozoan)
One with higher rate of growth: Extinction of slower grower
With different food supplies:
Coexistence
Diatom experiment
David Tilman, University of
Minnesota
Asterinella formosa (Af) and
Synedra ulna(Su) compete for
silica for the formation of cell
walls.
Adequate silica, coexist
Insufficient silica, Su drove Af to
extinction
13. 4 Competitive exclusion
principle
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Complete competitors can not coexist.
One species must go extinct
Complete competitions: two species that
live in the same place and possess exactly
the same ecological requirements.
Assumptions:
• Exactly the same resource requirement
(no more, no less)
• Environmental conditions remain
constant
Most of the time species can coexist
13.5 Competition is influenced by
non-resource factors
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Many non-resource factors would
influence the outcomes of the
competition. For example, space,
light.
Favor species with high
photosynthetic rate, allocate C to
height growth and leaves production
(fast-grow species)
Patterns of seed germination along
T gradient
Fakhri Bazzaz,
Harvard University
(Retired)
Five annual species
T influences the
germination, thus
seedling
establishment,
resource competition
and structure of
community.
13.6 Temporal variation in
environment influences competition
interactions
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As environmental
conditions vary,
the competition
advantages change
No one species can
reach sufficient
density to displace
its competitors;
Thus lead to coexist.
Shift in dominant grass species caused by moisture
13.7 Competition occurs for
multiple resources
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Systems are not simple one resource situations
• Usually competition for more than one resource
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Territorial defense against wide range of other species
Plants
• Monoculture
• Root competition
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Skeleton weed reduce by 35%
• Shoot competition
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Skeleton weed reduced by 53%
• Root and shoot competition
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Skeleton weed reduced by 69%
• Thus clover superior to skeleton weed for all resources
13.8 Relative competition abilities
change along environmental gradients
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Effect of
interspecific
competition across
an environmental
gradient
Note changes in
response when in
mixture
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Similar effect for
summer annuals and
moisture gradient
Also happens in
nature with water,
anoxia and salt stress
in a salt marsh
Chipmunks
Alpine
Cold tolerant
Lodgepole
Most
aggressive
Needs shade
Yellow Pine
aggressive
Least
Heat
tolerant
13.9 Niche of a species
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Concepts of niche
• describes how an organism or population responds to
the distribution of resources and competitors (e. g., by
growing when resources are abundant, and predators,
parasites and pathogens are scarce) and how it in turn
alters those same factors.
• dimensions of a niche: represent different biotic and
abiotic variables.
• These factors may include descriptions of the organism's
life history, habitat, trophic position (place in the food
chain), and geographic range.
• According to the competitive exclusion principle, no two
species can occupy the same niche in the same
environment for a long time.

Concepts of niche
• Fundamental niche: range of conditions
and resources a species can use to
survive and reproduce under no
interference by other species
• Realized niche: portion of fundamental
niches that a species actually exploits as
a result of interactions with other
species (e.g., competition).
Examples
Distribution of twp species of
cattail (Typha latifolia and T.
angustifolia)
Fundamental Niche:
Tl: water depth: -20~ 70 cm
Ta:
-20~110 cm
Realized Niche:
Tl: -20 ~ 70 cm
Ta: 20 ~ 110 cm (Changes)
Niche overlap: 20-70 cm
Fundamental and realized niches
Competition release
A species expands its niche in
response to the removal of a
competitor
Two examples
Response of Stipa neomexicana
plants
Commercial whaling in Antarctic
Ocean
Response of Stipa neomexicana plants
Jessica
Gurevitch
University of
New York at
Stony Brook
Stipa: C3
perennial
grass
Semi-arid
grassland in
Arizona
Commercial whaling in Antarctic Ocean
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Baleen whales: 1
million a century ago
eat Antarctic krill (4%
of body weight)
Now, less than
200,000
Other krill-dependent
predators such as
seals and penguins
have been found
greatly increased in
abundance
Competition release due to the
dramatic decrease in baleen whale
population
13.10 Resource partitioning
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“Complete competitors can not co-exist”
Why did not the best competitor force
others out?
Co-existing species must be different in
the use of resources
Niche differentiation: differences in the
range of resources used or environmental
tolerance
Examples:
• Plants grow together
• Animals share the same habitat
Resource partitioning
Use water and nutrients at
different depths
Spatial differentiation.
Resource partitioning
Size (diameter) of canine teeth for small cat that co-occur in
Israel. Size is correlated with size of prey selected by different
species.
Morphological differentiation.
Another example
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Seven Anolis lizards in tropical rainforest
Share common food needs — mainly insects.
They avoid competition by occupying different
sections of the rainforest
• the leaf litter floor
• shady branches
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All resources are subject to partitioning, such as
space, food, nesting sites.
This minimizes competition between similar
species.
(Temporal differentiation.)
Niche dimensions
Rarely do two or more species possess exactly
the same combination of requirement.
Species may overlap on one D of the niche,
but not on another.
13.11 Competition can influence
natural selection
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Competition is at the heart of Darwin’s theory of natural
selection. Characteristics that enable an organisms to
reduce competition will function to increase fitness.
Character displacement
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The outcome of the competition was
a shift in feeding niches. When the
shift involves features of the species’
morphology, behavior, or physiology
The process of evolution toward
niche divergence in the face of
competition
13.12 Competition involves both
biotic and abiotic factors
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Removal experiment is an effective method to
study competition
Hidden treatment effects: removal changes space,
light, soil temperature, and moisture, evaporation.
Competition is a complex interaction involving a
variety of environmental factors that directly
influence survival, growth, and reproduction.
Outcome of competition may differ markedly under
different set of environmental conditions.
End
FACILITIES MANAGEMENT
DEPARTMENT
DEPARTMENTAL NOTIFICATION
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LOCATION
CAMPUS-WIDE
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PROJECT
IN RESPONSE TO THE DROUGHT AND HEAT THIS
SUMMER, ALL TREES THAT HAVE EXCEEDED THEIR
PERMANENT WILTING POINTS WILL BE REMOVED
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DURATION
TWO DAYS, OCTOBER 15-16, 2007 (FALL BREAK)
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Science 12 October 2007:
Vol. 318. no. 5848, pp. 268 – 271
Reports
Functional Divergence of Former Alleles in
an Ancient Asexual Invertebrate
Natalia N. Pouchkina-Stantcheva, et al.
Theory suggests it should be difficult for asexual
organisms to adapt to a changing environment
because genetic diversity can only arise from
mutations accumulating within direct
antecedents and not through sexual exchange.
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Science Reports (cont.)
Functional Divergence of Former Alleles in
an Ancient Asexual Invertebrate
Natalia N. Pouchkina-Stantcheva, et al.
In an asexual microinvertebrate, the bdelloid
rotifer, we have observed a mechanism by which
such organisms could acquire the diversity
needed for adaptation. Gene copies most likely
representing former alleles have diverged in
function so that the proteins they encode play
complementary roles in survival of dry
conditions.
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Science Reports (cont.)
Functional Divergence of Former Alleles in
an Ancient Asexual Invertebrate
Natalia N. Pouchkina-Stantcheva, et al.
One protein prevents desiccation-sensitive
enzymes from aggregating during drying,
whereas its counterpart does not have this
activity, but is able to associate with
phospholipid bilayers and is potentially involved
in maintenance of membrane integrity. The
functional divergence of former alleles observed
here suggests that adoption of asexual
reproduction could itself be an evolutionary
mechanism for the generation of diversity.
Al Gore, UN panel share
Nobel for Peace
Al Gore &
U.N.'s IPCC (Intergovernmental
Panel on Climate Change)
For Global warming