Chap.8 Competition and coexistence 鄭先祐 生態主張者 Ayo [email protected].
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Transcript of Chap.8 Competition and coexistence 鄭先祐 生態主張者 Ayo [email protected].
chap08 Competition and coexistence 2
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
Road Map
chap08 Competition and coexistence 3
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
Road Map
chap08 Competition and coexistence 4
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.
chap08 Competition and coexistence 5
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
chap08 Competition and coexistence 6
Summary of biotic interactions
chap08 Competition and coexistence 7
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
chap08 Competition and coexistence 8
Aphid suckingleaf sap
Caterpillarchewing leaf
Intraspecific competitionbetween members of thesame species.
Interspecific competition between different species.
Interference competition: Each caterpillar physically intimidates the others
Resource competiton: each caterpillar chews as much leaf as it can
Fig.8.2 the different types of competition in nature
chap08 Competition and coexistence 9
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
chap08 Competition and coexistence 10
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
chap08 Competition and coexistence 11
Mean d
ry w
eig
ht
per
pla
nt,
g
10
10
1
10
10
10
10
10
10
10 1 10 10 10 10 10
1
2
3
4
5
6
-1
-2
-1 1 2 3 4 5
Number of plants per m 2
Fig. 8.3 Self-thinning in plants .
chap08 Competition and coexistence 12
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
chap08 Competition and coexistence 13
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)
chap08 Competition and coexistence 14
10
20
30
40
50
60
70
80
90
100
0
Hot Temperate
Wet
Cold Hot Temperate
Dry
Cold
T. confusum
T. castaneum
Perc
en
t w
ins
T. confusum generally wins in dry conditions
T. castaneum did better in moist environments
chap08 Competition and coexistence 15
T.castaneum
T.confusum
bI bII bIII bIV bI bII bIII bIV bI bII bIII bIV bI bII bIII bIV0
10
20
30
40
50
60
70
80
90
100Perf
ect
win
s
CI CII CIII CIV
Genetic strain of beetle
Fig. 8.5 Results of competition between different strains of flour beetles.
chap08 Competition and coexistence 16
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
chap08 Competition and coexistence 17
40
80
60
100
20
0
40
80
60
100
20
0
40
80
60
100
20
0
A. chrysomphali
A. melinusA. lagnanensis
A. chrysomphali displaced byA. lagnanensis on oranges
No competitive displacement
Competitive displacement ofA. lagnanensis
(a) Orange County
(b) Santa Barbara
(mild)
(c) San Fernando Valley (hot)
1 2 3Year
Perc
ent
of
ind
ivid
uals
Fig. 8.6 interspecific competition: replacement of one parasite by another in the orange gwoves of California
chap08 Competition and coexistence 18
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
chap08 Competition and coexistence 19
ABBCCD
ABACADBCBDCD
A B C D
A C
Ant Beetle Mouse Bird
Ant Mouse
Resource spectrum,(for example grain size)
Reso
urc
e u
tiliz
ati
on
Reso
urc
e s
upp
ly
a)
b)
Fig. 8.7
•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) 。
倘若只有兩種,互動的可能就只有一個。
chap08 Competition and coexistence 20
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
chap08 Competition and coexistence 21
Freshwater
Marine Habitat
Terrestrial
Vertebrates
Invertebrates
Taxa
Carnivores
Herbivores
Plants
70 60 50 40 30 20 10 0
Percent competition Fig. 8.8
chap08 Competition and coexistence 22
Mechanisms of interspecific competition
1. Consumptive (exploitative)
2. Preemptive
3. Overgrowth
4. Chemical
5. Territorial
6. Encounter •P.120-121
chap08 Competition and coexistence 23
Table 6.2 Mechanisms of interspecific competition
Consumptive competition is the most common form of competition, occurring in 37.8% of cases.
chap08 Competition and coexistence 24
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
chap08 Competition and coexistence 25
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.
chap08 Competition and coexistence 26
Fig. 8.9 mean size of the effect of competition on biomass for carnivores, filter feeders, herbivores, and primary producers.
chap08 Competition and coexistence 27
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
chap08 Competition and coexistence 28
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
chap08 Competition and coexistence 29
Modeling Competition
– For species 1; dN1 /dt = r1N1 [(K1 - N1 - N2) / K1]
– For species 2; dN2/dt = r2N2 [(K2 - N2 - N1)/ K2] = per capita competitive effect of species 2 on
species 1
• = per capita competitive effect of species 1 on species 2
• dN1 /dt = 0: zero-growth isocline
• Four possible outcomes (Figure 8.12)
chap08 Competition and coexistence 30
Fig. 8.10 conceptualization of conversion factors and
chap08 Competition and coexistence 31
Fig. 8.11 changes in the population size of species 1 when competing with species 2.
chap08 Competition and coexistence 32
N
NN
2 N 2
N
NN
N2 2
Region of increase of N only1
Region of increase of N only2
2Region of increase of N and N1
1.
2.
3.
Species 2 eliminated Species 1 eliminated
Either species 1 or species 2 eliminated
Both species coexist
2
2
2
2
1
1
1
1
1
00
0 0
1
1
1
2
2 2
21 1
11
1
dN
dt2
1dN
dt= 0
= 0
1dNdt
= 0
1dNdt
= 0
1dNdt
= 01dN
dt= 0
2
>
<
2
1
Fig. 8.12
chap08 Competition and coexistence 33
2
4
6
8
10
12
14
0.2
1.0
1.8
Alc
ohol
conce
ntr
ati
on (
%)
10 20 30 40 50 60 70
Pure populations
K = 13.0
Mixed populations
Pure populations
(a)
Volume of yeast, purepopulations
Volume of yeast, mixed populations
Alcohol concentration, pure populations
1
2
3
4
5
6
20 40 60 80 100 120 140
Pure populations K = 5.82
Mixed populations
Schizosaccharomyces
Time (hr)
Saccharomyces
(b)
Volu
me o
f yeast
1
Test of equations
chap08 Competition and coexistence 34
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 specified
chap08 Competition and coexistence 35
N increase
N increase
N and N increase
1
2
1 2
Equilibrium
K 1
1N
N2
K 2
K1/
2/K
•Fig. 8.14 Nonlinear Lotka-Volterra isoclines.
chap08 Competition and coexistence 36
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
chap08 Competition and coexistence 37
Gro
wth
or
loss
rate
Gro
wth
or
loss
rate
Pop
ula
tion s
ize
(a)
(b)
(c)100
Species A
Species B
Species A
Species B
Loss
100 R*A
0 R*B
Loss
Growth
Resource level (R)
Time0 0
Growth
10
R*BR*
Reso
urc
e level (R
)
•Fig. 8.15 Tilman’s R star concept of competition between two species A and B, based on their resource utilization curves.
•Initially grows faster than species B
•Outcompetes species A, as resources become more scarce.
chap08 Competition and coexistence 38
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
chap08 Competition and coexistence 39
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)
chap08 Competition and coexistence 40
By h
ab
itat
0
10
20
Num
ber
of
speci
es
pair
sSegre
gati
ng a
cross
diff
ere
nt
axes
By g
eogra
phy
By f
eedin
g h
abit
at
By s
ize
By w
i nt e
r ra
nge
No s
epara
tion
•Fig. 8.16 Type of separation among 40 species.
chap08 Competition and coexistence 41
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.
chap08 Competition and coexistence 42
• 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
chap08 Competition and coexistence 43
chap08 Competition and coexistence 44
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
chap08 Competition and coexistence 45
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.
chap08 Competition and coexistence 46
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
chap08 Competition and coexistence 47
Reso
urc
e u
tiliz
ati
on
Resource availability, K
Resource spectrum (x)
d
A B C
w
Fig. 8.19 Resource partitioning. Three species with similar, normal resource utilization curves utillization curves utilize a resource supply K.
•d= distance apart of means.
•w=standard deviation of resource utilization,
•d/w= resource separation ratio
chap08 Competition and coexistence 48
a
b
a
c
b
c
1
1
2
1
2
2
a
b
c
a
b
c
A B C
B C B C1 1 1 2 2 2A
First niche dimension
Seco
nd
nic
he d
imensi
on
A
•Fig. 8.20
chap08 Competition and coexistence 49
1
2
3
4
5
6
7
8
20
20
20
20
20
20
50
50
50
Leaf pairs N2
Distribution of insect A
Distribution of insect B
P.S. = 0 + 0.166 + 0.166 + 0 + 0 + 0 + 0 + 0 = 0.333
N1
•Fig. 8.21
chap08 Competition and coexistence 50
Species A
Species B
0.4
0.3
0.2
0.1
0 4 5 6 72 31 8
Resource set
Pro
port
ion
•Fig. 8.22
chap08 Competition and coexistence 51
Coexistence of Species
• Niche overlap between two insect species that feed on a shrub– Measured quantity
• PS = pi
• PS = proportional similarity = 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
chap08 Competition and coexistence 52
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
–
chap08 Competition and coexistence 53
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
chap08 Competition and coexistence 54
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%)
chap08 Competition and coexistence 55
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