Transcript Chap.8 Competition and coexistence

Chap.8
Competition and coexistence
鄭先祐
生態主張者 Ayo
[email protected]
Road Map
1. Forms of competition: Interspecific and
intraspecific
2. Intraspecific competition
– Common in nature
– Described by the 3/2 thinning law
3. Interspecific competition
–
Common in nature
–
Outcome affected by
•
•
Physical environment
Other species
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Road Map
4. Competition
– Exists among 55-75% of the species
– Mechanism: over use of the same resource
5. Mathematical models, called Lotka-Volterra
models, predict four outcomes of competition
– One species eliminated
– The other species is eliminated
– Both species coexist
– Either species is eliminated, depending on starting
conditions
6. Competing species can coexist through
partitioning of resources
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8.1 Species Interactions
• Herbivory, predation, parasitism(Table 8.1)
• Positive for one population
– Negative for the other population
• Batesian mimicry
– Mimicry of a non-palatable species by a palatable one
– Positive for one population
– Negative for the other population
• Amensalism
– One-sided competition
– One species had a negative effect on another, but the
reverse is not true.
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Species Interactions
• Neutralism
– Coexistence of noninteracting species
– Probably rare
• Mutualism and commensalisms
– Less common
– Symbiotic relationships
– Species are intimately associated with one another
– Both species may NOT benefit from relationship
– Not harmful, as is the case with parasitism
• Competition
– Negative effect for both species
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Summary of biotic interactions
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Types of competition
• Types of competition
– Interspecific
– Intraspecific
• Characterizing competition
– Resource competition
• Organisms compete for a limiting resource
– Interference competition
• Individuals harm one another directly by
physical force
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Intraspecific competition
between members of the
same species.
Resource competiton:
each caterpillar chews
as much leaf as it can
Interference competition:
Each caterpillar
physically intimidates the
others
Interspecific competition
between different species.
Aphid sucking
leaf sap
Fig.8.2 the different
types of competition
in nature
Caterpillar
chewing leaf
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8.2 Intraspecific competition
plants vs. animals
• Quantifying competition in plants vs.
animals
– For plants, expressed as change in biomass
– For animals, expressed as change in numbers
– Plants can not escape competition
– Animals can move away from competition
– Yoda (1963)
• Quantify competition between plants
• Yoda's Law or self-thinning rule; 3/2 power rule
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Law or self-thinning
• Yoda (1963) (cont.).
– Describes the increase in biomass of individual plants as
the number of plant competitors decrease.
– Log w = -3/2 (log N) + log c
– w = mean plant weight
– N = plant density
– C = constant
– w = cN3/2
– Figure 8.3
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Mean dry weight per plant, g
10 6
10 5
Fig. 8.3 Self-thinning in
plants .
10 4
103
10 2
10 1
1
10 -1
10 -2
10-1
1
101
102
103
104
Number
of plants
per m 2
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8.3 Interspecific competition
• Field experiments
– Organisms can interact with all other
organisms
– Natural variations in the abiotic environment
is factored in
• Laboratory experiments
– All important factors can be controlled
– Vary important factors systematically
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Thomas Park competition
experiments
– Tribolium castaneum and Tribolium confusum (Figure
8.4a)
– Large colonies of beetles can be grown in small
containers
– Large number of replications
– Observed changes in population sizes over two-three
years
– Waited until one species became extinct
– Cultures were infested with a parasite Adelina
• T. confusum won 89% of the time
– Without the parasite, no clear winner
– Microclimate effects (Figure 8.4)
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T. confusum generally wins in
dry conditions
100
90
Percent wins
80
70
60
50
40
30
20
10
0
Hot
Temperate
Cold
Hot
Temperate
Wet
T. castaneum
T. confusum
Cold
Dry
T. castaneum did better in moist
environments
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100
90
80
Perfect wins
70
60
50
40
30
20
10
0
bI bII bIII bIV
CI
bI
bII bIII bIV
bI bII bIII bIV
CII
CIII
bI bII
bIII bIV
CIV
Genetic strain of beetle
Fig. 8.5 Results of competition
between different strains of
flour beetles.
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T.castaneum
T.confusum
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Interspecific competition:
Natural systems
• Assessing the importance of competition
– Remove species A and measure the
response of species B
– Difficult to do outside of laboratory
• Migration problems
• Krebs or Cage effect (p.115)
– Examples in nature
• Parasitic wasps
• Figure 8.6
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(a) Orange
County
100
A. chrysomphali displaced by
A. lagnanensis on oranges
80
60
40
20
(b) Santa
Barbara
(mild)
(c)
San
Percent of individuals
0
Fernando
Valley
(hot)
100
No competitive displacement
A. chrysomphali
80
A. lagnanensis
A. melinus
60
40
20
0
100
80
60
40
20
Competitive displacement of
A. lagnanensis
Fig. 8.6 interspecific
competition:
replacement of one
parasite by another in
the orange gwoves of
California
0
1
2
3
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The Frequency of Competition
• Joe Connell (1983)
– Competition was found in 55% of 215 species
surveyed (Figure 8.7)
– Effects of number of competing species
• Single pairs: competition was almost always
reported (90%)
• Multiple species, competition was reported in
50% of the studies
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•倘若有ABCD四種，其可能的互動有c(4,2)=6個，
但實質會有重疊到的互動只有3個，所以可能發生
competition的機率是50% (3/6)。
Resource utilization
b)
Resource supply
a)
A
B
C
D
Ant
Beetle
Mouse
Bird
AB
AC
AD
BC
BD
CD
倘若只有兩種，互動的可能就只有一個。
A
Ant
Fig. 8.7
AB
BC
CD
C
Mouse
Resource spectrum,
(for example grain size)
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Differing opinions
- Schoener (1983)
• Common flaws of studies
– Positive results tend to be more readily
– Scientists do not study systems at random - may work
in systems where competition is more likely to occur
• Failure to reveal the true importance of
competition in evolution and ecological time
– Most organisms have evolved to escape competition
and lack of fitness it may confer
– Competition may only occur infrequently and in years
where resources are scarce
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Freshwater
Marine
Habitat
Terrestrial
Vertebrates
Invertebrates
Taxa
Carnivores
Herbivores
Plants
70
60
50
40
30
20
10
Percent
competition
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Fig. 8.8
21
Mechanisms of interspecific
competition
1. Consumptive (exploitative)
2. Preemptive
3. Overgrowth
4. Chemical
5. Territorial
6. Encounter
•P.120-121
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Table 6.2 Mechanisms of
interspecific competition
Consumptive competition is the most common form of
competition, occurring in 37.8% of cases.
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Amensalism
• Asymmetric competition is often called
amensalism and may be particularly
important in plants, wherein one species
might secrete chemicals from its roots
which inhibit the growth of other plants
that do not secrete such chemicals.
• Allelopathy
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Differing views of competition
• Gurevitch et al. 1992
– Examined on 93 species
– Primary producers and carnivores did not
show strong effects of competition as did filter
feeders and herbivores. (fig. 8.9)
– No differences in the effects of competition in
terrestrial, freshwater, or marine systems, for
plants or carnivores, or in high-productivity
versus low-productivity systems.
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Fig. 8.9 mean size of the effect of competition on biomass for
carnivores, filter feeders, herbivores, and primary producers.
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Grime-Tilman debate
• Grime 1979
– Competition unimportant for plants in
unproductive environments
• Tilman 1988
– Competition occurs across all productivity
gradients
• Gurevitch’s result supports Tilman
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8.5 Modeling Competition
• Based on logistic equations for population
growth
• Growth equations for two populations
coexisting independently
– For species 1; dN1 /dt = r1N1 [(K1- N1) / K1]
– For species 2; dN2 /dt = r2N2 [(K2 - N2) / K2]
• r = per capita rate of population growth
• N = population size
• K = carrying capacity
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Modeling Competition
– For species 1; dN1 /dt = r1N1 [(K1 - N1 - aN2) / K1]
– For species 2; dN2/dt = r2N2 [(K2 - N2 - bN1)/ K2]
 a = per capita competitive effect of species 2 on
species 1
• b = per capita competitive effect of species 1 on
species 2
• dN1 /dt = 0: zero-growth isocline
• Four possible outcomes (Figure 8.12)
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Fig. 8.10
conceptualization of
conversion factors a
and b
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Fig. 8.11 changes in the population size of
species 1 when competing with species 2.
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N2
k1
a
Species 2 eliminated
k1
k
a > 2
k2
<k1
dN 2
=0
dt
b
k2
dN 1
dt
0
N2
k2
k2
N2
k2
dN 1
=0
dt
k1
dN 1
=0
dt
a
=0
k1
N1
0
b
Either species 1 or
species 2 eliminated
N2
k1
a
k2
k1
a
Species 1 eliminated
k1
k2
N1
b
Both species coexist
dN 1
=0
dt
dN 1
=0
dt
0
k2
k1
N1
0
1.
b
Region of increase of N 1 only
2.
Region of increase of N 2 only
3.
Region ofchap08
increase
of N 1 and
N2
Competition
and coexistence
k1
k2
N1
b
Fig. 8.12
32
1.8
K1 = 13.0
Pure
populations
Pure
populations
10
1.0
8
6
Mixed
populations
4
2
10
Volume of yeast
(b)
Saccharomyces
20
30
40
50
60
0.2
Alcohol
concentration (%)
(a) 14
12
70
Volume of yeast, pure
populations
Volume of yeast, mixed
populations
Alcohol concentration,
pure populations
6
Pure populations K 2 = 5.8
5
4
3
2
1
Mixed populations
Test of
equations
Schizosaccharomyces
20 40 60 80 100 120 140
Time (hr)
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Lotka-Volterra 公式的缺陷
• The maximal rate of increase, the competition
coefficients, and the carrying capacity are all
assumed to be constant
• There are no time lags
• Field tests of these equations have rarely been
performed
• Laboratory tests have shown divergence
– Figure 8.14
• Mechanisms that drive competition are not
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N 1 increase
K 1/a
N 2 increase
N1 and N 2 increase
K2
Equilibrium
N2
K1
N1
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•Fig. 8.14
Nonlinear LotkaVolterra isoclines.
K 2/b
35
R star concept
• R* - Tilman (1982, 1987) alternative
– Need to know the dependence of an
organism's growth on the availability of
resources
– Figure 8.15
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•Outcompetes
species A, as
resources
become more
scarce.
(c)
Growth
Loss
0 R*A
10
Species B
Growth
Loss
0 R*B
10
Resource level (R)
100
Population size
•Initially grows
faster than
species B
Species A
Species A
Species B
R*
0
Time
Resource level (R)
(b)
Growth or loss rate Growth or loss rate
(a)
•Fig. 8.15
Tilman’s R
star concept
of competition
between two
species A and
B, based on
their resource
utilization
curves.
R*B
0
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8.6 Coexistence of species
• Niche
– Grinnell (1918): a subdivision of a habitat that contains
an organism's' dietary needs, its temperature,
moisture, pH, and other requirements
– Elton (1927) and Hutchinson (1958): an organism's
role within the community
• Gause: two species with similar requirements
could not live together in the same place
– Hardin (1960): Gause's principle, known as competitive
exclusion principle, where direct competitors cannot
coexist
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Coexistence of species
• David Lack: Competition and coexistence in
about 40 pairs of birds, mediated by habitat
segregation.
– Figure 8.16
• Examples of coexistence
– Darwin's finches on the Galapagos
– Terns on Christmas Island (Ashmole 1968)
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10
By feeding habitat
By geography
By habitat
Number of species pairs
Segregating across different axes
20
•Fig. 8.16 Type of separation
among 40 species.
0
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Resource partitioning
• Ranks for resource partitioning
– (Schoener 1974)
– Macrohabitat (55%)
– Food type (40%)
– Time of day or year (5%)
• Habitat was of most importance in
separation species.
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• Hutchinson (1959)
– Seminal paper, "Homage to Santa Rosalia, or
why are there so many kinds of animals?"
– Examined size differences for
• Sympatric species (species occurring together)
• Allopatric species (occurring alone)
• Table 8.3
• Hutchinson's ratio, 1.3
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Criticism of Hutchinson
• Studies that supported Hutchinson - inappropriate
statistics
• Further tests showed no differences between
species than would occur by chance alone.
• Size-ratio differences could have evolved for other
reasons
• Biological significance cannot always be attached
to ratios, particularly to structures not used to
gather food. Figure 8.17
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Fig. 8.17 A ratio of 1:1.3 has been found to
occur between members of sets of kitchen
knives, skillets, musical recorders, and
children’s bicycles.
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Support of Hutchinson
• Figure 8.18 d/w analysis for separation
on continuous resource sets
– Figure 8.19
– Figure 8.20
– Discontinuous resource distribution
• Figure 8.21
• Figure 8.22
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•d= distance apart of means.
•w=standard deviation of resource utilization,
Resource utilization
•d/w= resource separation ratio
Resource availability, K
d
A
B
C
w
Resource spectrum (x)
Fig. 8.19 Resource partitioning. Three species with similar, normal resource
utilization curves utillization curves utilize a resource supply K.
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Second niche dimension
a1
b1
a
a
a2
c1
b2
b
b
c
c
c2
A
A1
•Fig. 8.20
B1
B
C
C1 A 2
B2
First and
niche
dimension
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Leaf pairs
N2
50
1
N1
2
20
50
3
20
50
4
20
5
20
6
20
7
20
8
Distribution of
insect A
Distribution of
insect B
•Fig. 8.21
P.S. = 0 + 0.166 + 0.166 + 0 + 0 + 0 + 0 + 0 = 0.333
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0.4
Species A
Proportion
0.3
0.2
Species B
0.1
0
1
2
3
4
5
Resource set
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•Fig. 8.22
8
50
Coexistence of Species
• Niche overlap between two insect species that
feed on a shrub
– Measured quantity
• PS = Spi
• PS = proportional similarity
 S = sum of all units, 1 to n, in resource set
• pi = proportion of least abundant member of pair
• PS < 0.70 indicates coexistence for single resource
• PS > 0.70 indicates competitive exclusion for single
resource
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Coexistence of Species
• Proportional similarity indices for two or
more resources can be combined
– Multiply separate PS values to
determine overall PS value
– Coexistence for two resources
– 0.7 x 0.7 = 0.49 or less
–
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Applied Ecology
• Is the release of multiple species of
biological control agents beneficial?
– Control of pests in agriculture is of paramount
importance
– Biological control is seen as a preferable
alternative to chemical control
• Release a variety of enemies against a pest
• Observe which enemy does the best job
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Biological control
• Is this the best strategy?
– Intensive competition for the prey leads to lower
effectiveness of the biological agents
– Greater population establishment rate with fewer
enemy species (Figure 1)
– Establishment rate of single-species releases were
significantly greater than the simultaneous release of
two or more species (76% vs. 50%)
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 問題與討論！
[email protected]
Ayo 台南站： http://mail.nutn.edu.tw/~hycheng/
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