chapter 8 competition and coexistence

Chapter 8Competition

and Coexistence

群體生態學 Synecology: community ecology

以生物組織水準來分1.個體生態學 Autecology: Life history,

adaptation

2.種群生態學 Population ecology

3.群體生態學 Synecology: community ecology

4.生態系統生態學 Ecosystem ecology

Outline• Forms of competition: Interspecific and

intraspecific• Intraspecific competition

– Common in nature– Described by the 3/2 thinning law

Outline• Interspecific competition

– Common in nature– Outcome affected by

• Physical environment• Other species

Outline• Competition

– Exists among 55-75% of the species– Mechanism: over use of the same resource

Outline• 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

Outline• Competing species can coexist through

partitioning of resources

Community ：群體，群聚，群落

• 群落是居住的相當靠近且有交互作用可能物種集合

• 生物在自然界依循一定的規律而集合成群落

• 特定空間或特定生境下若干生物種群有規律的組合

• 彼此間或與環境間互相作用與影響，具有一定形態結構與營養結構，執行一定功能

Community 群落 A group of populations of plants and animals in a given place; used in a broad sense to refer to ecological units of various sizes and degrees of integration.

福壽螺為什麼要把卵產在枝幹上？

Three types of Community ：群體，群聚，群落

1. Abstract community 抽象群聚：心裡想像的特殊形式群聚，事實上並不存在，如沙漠，草原群聚

2. Associational community 聯合群聚：過渡形式的生物群聚，如森林，草原，池塘

3. Concrete community 具體群聚：可直接觀察的特殊區域（ 1 ） Global community 全球性群聚：陸地

terrestrial ，海洋 oceanic（ 2 ） Regional community 區域性群聚 =Biotic

province 生物領域（根據溫度、雨量等不同、將全世界分成：冷溫熱三區（下含 16 個生物相 Biome)

群落（體）生態學 Synecology: community ecology

Competition

Predation

Community structure

Species diversity

succession

群落的基本特徵

1.具有一定種類組成2.不同物種間相互影響3.形成群落環境4.具有一定結構5.一定的動態形式6.一定的分布範圍7.群落的邊界特徵

#14Chapt. 08

馬拉威湖慈鯛科的適應性演化

Interactions among species:種間的關係

( 一 ) 競爭 competition

( 二 ) 互惠 mutualism

( 三 ) 共棲 commensalism

( 四 ) 共生和附生 protocooperation

( 五 ) 寄生 parasitism

( 六 ) 捕食 predation

The evolution of interactions among species(I)• Mimicry 擬態：從模仿其他物種的外表上獲得好處的現象。

• Bastesian mimicry 貝氏擬態：無毒害的物種藉由模擬有害物種而獲利的情形。

• Mullerian mimicry 木氏擬態 : 兩種不同物種之間的擬態。

• Aggressive mimicry 攻擊性擬態：有毒的種類模擬無毒的種類，以提升其偽裝效果，增加掠食成功率。

The evolution of interactions among species(II)• Coevolution 共同演化：例如植物和昆蟲間的共同演化。

• Parasitism 寄生 :

• Mutualism 互利共生：• Competition 競爭：• Predator-prey 掠食者與獵物：• Herbivore-plant 草食性動物與植物：

血桐的蜜線

Why are community interactions important?

• 群體是居住的相當靠近且有交互作用可能物種集合

• 烏頭翁和白頭翁混居的結果會如何？• 草原上只有羚羊而沒有獅子，結果會如何？

• 如果沒有蝴蝶或蜜蜂，開花植物的世界將會如何？

動物可以消滅植物嗎？

這麼多的小螃蟹都可以長大嗎？

這些小鰻苗為什麼要力爭上游？

群聚的利己主義與交互作用假設的檢驗

日本禿頭鯊和蝦苗

小蘭嶼火山口

在寄主與寄生系統中快速的族群改變

一群共域棲息蜥蜴的資源分配現象

Niche: 生態龕、生態位、生態區位

. The sum total of a population’s use of the biotic and abiotic resources of its environment; the role a population plays in its environment. 一個生物在它所生存的環境中，對於生物性與非生物性資源利用的總和。

. The niche is a property of the species or population; it is defined functionally or in terms of the species’ tolerance limits

影響生物的因子• 非生態因子 Non-ecological factors:

– 對有機體生活無明顯影響的環境因子。• 生態因子 Ecological Factors

– 生物性因子 Biotic factors（一）共生（二）天敵（三）競爭（四）抑制（五）傳播

– 非生物性因子 Abiotic factors

山櫻花為什麼先開花後長葉子？

自然競爭的實驗性證據

實驗室中草履蟲族群的競爭

實驗室中掠食者和獵物之間的動態關係

邏輯模型所預測的族群成長情形

指數成長和對數成長的比較

Lotka-Volterra model:

• 獵物按指數增長，捕食者沒有獵物時按指數減少的世代連續模型。

• dN1/dt = r1N1[(K1-N1)/K1]

• dN2/dt = r2N2[(K2-N2)/K2]R = population growth rate

N = population size

K =carrying capacity

Lotka-Volterra model: 獨立時• （ 1 ）獵物 prey

dN/dt = r1NN = prey densityt = timeR1 = population growth rate

• （ 2 ）捕食者 predatordP/dt = -r2PN = predator densityt = timeR1 = population mortality rate

Aphid suckingleaf sap

Caterpillarchewing leaf

Intraspecific competitionbetween members of thesame species.

Interspecific competition between different species.

Species Interactions• Types of

competition

Species Interactions• Summary of biotic interactions (Table 8.1)

Species Interactions• Summary of biotic interactions (cont.)

– Herbivory, predation, parasitism• Positive for one population• Negative for the other population

– Batesian mimicry• Mimicry of a non-palatable species by a palatable

one

Species Interactions– Batesian mimicry (cont.).

• 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.

Species Interactions– Neutralism

• Coexistence of noninteracting species• Probably rare

– Mutualism and commensalisms• Less common• Symbiotic relationships

Species Interactions– Mutualism and commensalisms (cont).

• 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

Species Interactions• Types of competition (cont.).

– Interspecific– Intraspecific

• Characterizing competition– Resource competition

• Organisms compete for a limiting resource

Species Interactions• Characterizing competition (cont.).

– Interference competition• Individuals harm one another directly by physical

force

Intraspecific Competition• 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

Intraspecific Competition• Quantifying competition in plants vs.

animals (cont.).– Animals can move away from competition– Yoda (1963)

• Quantify competition between plants• Yoda's Law or self-thinning rule; 3/2 power rule

Intraspecific Competition– 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

Intraspecific Competition– Yoda (1963) (cont.).

• w = cN3/2

Interspecific Competition: Laboratory Experiments

• 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


• Thomas Park competition experiments– Tribolium castaneum (Figure 8.4a) and

Tribolium confusum


• Thomas Park competition experiments (cont). – Large colonies of beetles can be grown in

small containers– Large number of replications


• Thomas Park competition experiments (cont).– Observed changes in population sizes over

two-three years


• Thomas Park competition experiments (cont). – Waited until one species became extinct


• Thomas Park competition experiments (cont). – Cultures were infested with a parasite Adelina


• Thomas Park competition experiments (cont). – T. confusum won 89% of the time Without the

parasite, no clear winner


• Thomas Park competition experiments (cont). – Microclimate effects (Figure 8.4)

10

20

30

40

50

60

70

80

90

100

0

Hot Temperate

Wet

Cold Hot Temperate

Dry

Cold

T. confusum

T. castaneum

Perc

ent

win

s


– Microclimate effects (cont.).• T. confusum did better in dry environments• T. castaneum did better in moist environments


• Thomas Park competition experiments (cont).– Mechanism of competition - predation of eggs


• Thomas Park competition experiments (cont).– Predatory tendencies varied with different

strains• Figure 8.5

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


• Interspecific competition: Natural systems– Assessing the importance of competition

• Remove species A and measure the response of species B


– Assessing the importance of competition (cont.).

• Difficult to do outside of laboratory– Migration problems– Krebs or Cage effect


– Assessing the importance of competition (cont.).

• Examples in nature– Parasitic wasps– Figure 8.6

40

80

60

100

20

0

40

80

60

100

20

0

40

80

60

100

20

0

A. chrysomphali

A. melinus

A. 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

en

t of

indiv

iduals


• Examples in nature (cont.).– Used to control scale pest

– Climate can alter competitive

The Frequency of Competition

• Joe Connell (1983)– Competition was found in 55% of 215 species

surveyed

– Figure 8.7

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

upply

a)

b)


• Joe Connell (1983) (cont.).– Effects of number of competing species

• Single pairs: competition was almost always reported (90%)


– Effects of number of competing species (cont.).• Multiple species, competition was reported in 50%

of the studies


• Joe Connell (1983) (cont.).– Differing opinions - Schoener (1983)


• Common flaws of studies– Positive results tend to be more readily


• Common flaws of studies (cont.).– 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


• Failure to reveal the true importance of competition (cont.).– Competition may only occur infrequently and

in years where resources are scarce


• Patterns of competition– Figure 8.8

Freshwater

Marine Habitat

Terrestrial

Vertebrates

Invertebrates

Taxa

Carnivores

Herbivores

Plants

70 60 50 40 30 20 10 0

Percent competition


• Mechanisms of competition (Schoener, 1963)– Table 8.2


• Mechanisms of competition (Schoener, 1963) (cont.).– Consumptive or exploitative– Preemtive– Overgrowth


• Mechanisms of competition (Schoener, 1963) (cont.).– Chemical

• Allelopathy

– Territorial


• Mechanisms of competition (Schoener, 1963) (cont.).– Encounter


• Differing views of competition– Gurevitch et al. 1992

• Found no differences in competition between different habitat types but did find filter feeders and herbivores competed more than carnivores or plants.


• Differing views of competition (cont.).– Grime 1979

• Competition unimportant for plants in unproductive environments


• Differing views of competition (cont.).– Tilman 1988

• Competition occurs across all productivity gradients

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]

Modeling Competition• Growth equations for two populations

coexisting independently (cont.).– For species 1; dN2 /dt = r2N2 [(K2 - N2) / K2]

• r = per capita rate of population growth

Modeling Competition– For species 1; dN2 /dt = r2N2 [(K2 - N2) / K2]

(cont.).• N = population size• K = carrying capacity• Subscripts refer to species

Modeling Competition• Populations that compete

– Conversion factor that quantifies the per capita competitive effect of one species on another

– For species 1; dN1 /dt = r1N1 [(K1 - N1 - aN2) / K1]

Modeling Competition• Populations that compete (cont.).

– For species 1; 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

Modeling Competition• Populations that compete (cont.).

– dN1 /dt = 0: zero-growth isocline– Four possible outcomes

• Figure 8.12

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

dNdt

2

1dNdt

= 0

= 0

1dNdt

= 0

1dNdt

= 0

1dNdt

= 01dN

dt= 0

2

>

<

2

1

Modeling Competition• Test of equations

– Figure 8.13

2

4

6

8

10

1214

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

Modeling Competition• Deficiencies

– The maximal rate of increase, the competition coefficients, and the carrying capacity are all assumed to be constant

– There are no time lags

Modeling Competition• Deficiencies (cont.).

– Field tests of these equations have rarely been performed

– Laboratory tests have shown divergence• Figure 8.14

N increase

N increase

N and N increase

1

2

1 2

Equilibrium

K1

1N

N2

K 2

K1/

2/K

Modeling Competition• Deficiencies (cont.).

– Mechanisms that drive competition are not specified

• R* - Tilman (1982, 1987) alternative– Need to know the dependence of an organism's growth on

the availability of resources– Figure 8.15

Gro

wth

or

loss

rate

Gro

wth

or

loss

rate

Popula

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* R

eso

urc

e level (R

)

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

Coexistence of Species• Niche (cont.).

– 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

Coexistence of Species• Hardin (1960): Gause's principle, known

as competitive exclusion principle, where direct competitors cannot coexist

Coexistence of Species• David Lack: Competition and coexistence

in about 40 pairs of birds, mediated by habitat segregation.– Figure 8.16

By h

abit

at

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

Coexistence of Species• Examples of coexistence

– Darwin's finches on the Galaapagos– Terns on Christmas Island (Ashmole 1968)

Coexistence of Species• Ranks for resource partitioning (Schoener

1974)– Macrohabitat (55%)– Food type (40%)– Time of day or year (5%)

Coexistence of Species• 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)

Coexistence of Species• Hutchinson (1959) (cont.).

– Examined size differences for (cont.).• Allopatric species (occurring alone)• Table 8.3

Coexistence of Species– Examined size differences for (cont.).

• Hutchinson's ratio, 1.3

– Criticism of Hutchinson• Studies that supported Hutchinson - inappropriate

statistics

Coexistence of Species– Criticism of Hutchinson (cont.).

• Further tests showed no differences between species than would occur by chance alone.

• Size-ratio differences could have evolved for other reasons

Coexistence of Species– Criticism of Hutchinson (cont.).

• Biological significance cannot always be attached to ratios, particularly to structures not used to gather food. Figure 8.17


– Support of Hutchinson– Figure 8.18 d/w analysis for separation on

continuous resource sets

Coexistence of Species– Figure 8.18 d/w analysis for separation on

continuous resource sets (cont.).• Figure 8.19

Reso

urc

e u

tiliz

ati

on

Resource availability, K

Resource spectrum (x)

d

A B C

w

Coexistence of Species• Figure 8.19 (cont.).

– d=distance between maxima– w = measure of spread

• Figure 8.20

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 n

iche d

imensi

on

A


– Discontinuous resource distribution• Figure 8.21

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

Coexistence of Species– Discontinuous resource distribution (cont.).

• Figure 8.22

Species A

Species B

0.4

0.3

0.2

0.1

0 4 5 6 72 31 8

Resource set

Pro

port

ion

Coexistence of Species– Discontinuous resource distribution (cont.).

• 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

Coexistence of Species– Measured quantity (cont.).

» 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

Coexistence of Species– Measured quantity (cont.).

» 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

Applied Ecology• Is the release of multiple species of

biological control agents beneficial?– Control of pests in agriculture is of paramount

importance

Applied Ecology• Is the release of multiple species of

biological control agents beneficial? (cont.).– Biological control is seen as a preferable

alternative to chemical control

Applied Ecology– Biological control viewed by some

• Release a variety of enemies against a pest• Observe which enemy does the best job

Applied Ecology– Biological control viewed by some (cont.).

• 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 for Box 1)

Applied Ecology• Is this the best strategy? (cont.).

– Establishment rate of single-species releases were significantly greater than the simultaneous release of two or more species (76% vs. 50%)

Summary• Competition may be interspecific or

intraspecific• Competition may be viewed as resource

competition or interference competition

Summary• Intraspecific competition between plants

may be described by the 3/2 self-thinning rule

Summary• Outcome of competition can be influenced

by– Environmental conditions– The presence or absence of natural enemies

Summary• Outcome of competition can be influenced

by (cont.).– The genetic strain of the competitors involved

Summary• Experimental studies show that in nature

competition occurs between different types of organisms over a broad scale– Such studies focused on exotics and

generalizations to natural ecosystems are questionable

Summary• Experimental studies show that in nature

competition occurs (cont.).– Competition between exotics and native

species• Serious consequences for natural ecosystems

Summary• Frequency of competition

– 55% to 75% of species involved– Competition is often asymmetric

• Six mechanisms of competition– Consumptive– Preemptive

Summary• Six mechanisms of competition (cont.).

– Overgrowth– Chemical– Territorial– Encounter

Summary• Lotka-Volterra model: early competition

model– Two species interaction– Four possible outcomes

• Species 1 becomes extinct• Species 2 becomes extinct

Summary– Four possible outcomes (cont.).

• Either species 1 or species 2 becomes extinct based on starting conditions

• Coexistence

Summary• Lotka-Volterra model: early competition

model (cont.).– Competition is minimized and species can

coexist if they use different resources• Hutchinson's 1:1.3 ratio

Summary– Competition is minimized and species can

coexist if they use different resources (cont.).• d/w values greater than unity• Proportional similarity values no greater than 70%

Discussion Question #1• Which type of competition would you

expect to be more important in nature?

Discussion Question #2• Much native vegetation in the Florida

Everglades is being lost. Could this be due to climate change or the influence of exotic invaders? Design an experiment.

Discussion Question #3• In the above question, how could you

determine the mechanism of competition? How could you differentiate among competition for light, water, or nutrients?

Discussion Question #4• In trying to understand how species

compete, what advantages are there in field observations, field experiments, laboratory experiments, and mathematical models?

Discussion Question #5• Using fully labeled graphs, explain the Lotka-

Volterra approach to competition theory. What predictive power does the Lotka-Volterra model have? How is Tilman's R* concept an improvement? What other improvements might you suggest?

chapter 8 competition and coexistence

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