53-communities text.ppt

8/11/2019 53-communities text.ppt

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Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures forBio logy, Seventh Edit ion

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 53

Community Ecology


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The various animals and plants surrounding

this watering hole Are all members of a savanna community in

southern Africa

Figure 53.1


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Concept 53.1: A communitys interactions

include competition, predation, herbivory,symbiosis, and disease

Populations are linked by interspecific

interactions

That affect the survival and reproduction of the

species engaged in the interaction


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Interspecific interactions

Can have differing effects on the populationsinvolved

Table 53.1


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Competition

Interspecific competition

Occurs when species compete for a particularresource that is in short supply

Strong competition can lead to competitive

exclusion

The local elimination of one of the two

competing species


7/88Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

The Competitive Exclusion Principle

The competitive exclusion principle

States that two species competing for thesame limiting resources cannot coexist in the

same place



Ecological Niches

The ecological niche

Is the total of an organisms use of the bioticand abiotic resources in its environment



The niche concept allows restatement of the

competitive exclusion principle Two species cannot coexist in a community if

their niches are identical



However, ecologically similar species can

coexist in a community If there are one or more significant difference

in their niches

When Connell removed Balanus from the lower

strata, the Chthamaluspopulation spread into that area.

The spread of Chthamaluswhen Balanus was

removed indicates that competitive exclusion makes the realized

niche of Chthamalusmuch smaller than its fundamental niche.

RESULTS

CONCLUSION

Ocean

Ecologist Joseph Connell studied two barnacle

species

Balanus balanoidesand Chthamalus stellatus

that have astratified distribution on rocks along the coast of Scotland.

EXPERIMENT

In nature, Balanusfails to survive high on the rocks because it is

unable to resist desiccation (drying out) during low tides. Its realized

niche is therefore similar to its fundamental niche. In contrast,

Chthamalusis usually concentrated on the upper strata of rocks. To

determine the fundamental of niche of Chthamalus,Connell removed

Balanusfrom the lower strata.

Low tide

High tide

Chthamalus

fundamental niche

Chthamalus

realized niche

Low tide

High tideChthamalus

Balanus

realized niche

Balanus

Ocean

Figure 53.2



As a result of competition

A species fundamental niche may be differentfrom its realized niche



A. insolitus

usually percheson shady branches.

A. distichus perches

on fence posts and

other sunnysurfaces.

A. dist ichus

A. r icordi i

A. insol i tus

A. chris tophei

A. cybotes

A. ether idgei

A. al inigar

Figure 53.3

Resource Parti tioning

Resource partitioning is the differentiation of

niches That enables similar species to coexist in a

community



G. fortis

Beak depth (mm)

G. fuliginosa

Beak

depth

Los Hermanos

Daphne

Santa Mara, San Cristbal

Sympatric

populations

G. fuliginosa,

allopatric

G. fortis,allopatricPercentagesofindividualsineachsizeclass

40

20

0

40

20

0

40

20

0

8 10 12 14 16

Figure 53.4

Character Displacement

In character displacement

There is a tendency for characteristics to be moredivergent in sympatric populations of two species

than in allopatric populations of the same two

species


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Predation

Predation refers to an interaction

Where one species, the predator, kills and eatsthe other, the prey


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Feeding adaptations of predators include

Claws, teeth, fangs, stingers, and poison

Animals also display

A great variety of defensive adaptations


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Cryptic coloration, or camouflage

Makes prey difficult to spot

Figure 53.5


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Aposematic coloration

Warns predators to stay away from prey

Figure 53.6


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In some cases, one prey species

May gain significant protection by mimickingthe appearance of another


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In Batesian mimicry

A palatable or harmless species mimics anunpalatable or harmful model

(a) Hawkmoth larva

(b) Green parrot snake

Figure 53.7a, b


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In Mllerian mimicry

Two or more unpalatable species resembleeach other

(a) Cuckoo bee

(b) Yellow jacketFigure 53.8a, b


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Herbivory

Herbivory, the process in which an herbivore

eats parts of a plant

Has led to the evolution of plant mechanical

and chemical defenses and consequent

adaptations by herbivores


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Parasitism

In parasitism, one organism, the parasite

Derives its nourishment from anotherorganism, its host, which is harmed in the

process


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Parasitism exerts substantial influence on

populations

And the structure of communities


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Disease

The effects of disease on populations and

communities

Is similar to that of parasites


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Pathogens, disease-causing agents

Are typically bacteria, viruses, or protists

M li


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Mutualism

Mutualistic symbiosis, or mutualism

Is an interspecific interaction that benefits bothspecies

Figure 53.9

C li


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Commensalism

In commensalism

One species benefits and the other is notaffected

Figure 53.10


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Commensal interactions have been difficult to

document in nature

Because any close association between

species likely affects both species

I t ifi I t ti d Ad t ti


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Interspecific Interactions and Adaptation

Evidence for coevolution

Which involves reciprocal genetic change byinteracting populations, is scarce


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However, generalized adaptation of organisms

to other organisms in their environment

Is a fundamental feature of life


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Concept 53.2: Dominant and keystone species

exert strong controls on community structure

In general, a small number of species in a

community

Exert strong control on that communitysstructure

S i Di it


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Species Diversity

The species diversity of a community

Is the variety of different kinds of organismsthat make up the community

Has two components


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Species richness

Is the total number of different species in thecommunity

Relative abundance

Is the proportion each species represents of

the total individuals in the community


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Two different communities

Can have the same species richness, but adifferent relative abundance

Community 1

A: 25% B: 25% C: 25% D: 25%

Community 2

A: 80% B: 5% C: 5% D: 10%

D

C

B

A

Figure 53.11


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A community with an even species abundance

Is more diverse than one in which one or twospecies are abundant and the remainder rare

Trophic Structure


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Trophic Structure

Trophic structure

Is the feeding relationships between organismsin a community

Is a key factor in community dynamics


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Food chainsQuaternary

consumers

Tertiary

consumers

Secondary

consumers

Primary

consumers

Primary

producers

Carnivore

Carnivore

Carnivore

Herbivore

Plant

Carnivore

Carnivore

Carnivore

Zooplankton

Phytoplankton

A terrestrial food chain A marine food chainFigure 53.12

Link the trophiclevels from

producers to top

carnivores

Food Webs


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Food Webs

A food web Humans

Baleen

whales

Crab-eater seals

Birds Fishes Squids

Leopard

seals

Elephant

seals

Smaller toothed

whalesSperm

whales

Carnivorous

plankton

Euphausids

(krill)

Copepods

Phyto-

plankton

Figure 53.13

Is a branchingfood chain with

complex

trophic

interactions


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L imits on Food Chain Length


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L imits on Food Chain Length

Each food chain in a food web

Is usually only a few links long

There are two hypotheses

That attempt to explain food chain length


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The energetic hypothesis suggests that the

length of a food chain

Is limited by the inefficiency of energy transfer

along the chain


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The dynamic stability hypothesis

Proposes that long food chains are less stablethan short ones


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Most of the available data

Support the energetic hypothesis

High

(control)

Medium Low

Productivity

No. of species

No. of trophic

links

Numberofspecies

Numberoftrophiclinks

0

1

2

3

4

5

6

0

1

2

3

4

5

6

Figure 53.15

Species with a Large Impact


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Species with a Large Impact

Certain species have an especially large

impact on the structure of entire communities

Either because they are highly abundant or

because they play a pivotal role in community

dynamics

Dominant Species


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Dominant Species

Dominant species

Are those species in a community that aremost abundant or have the highest biomass

Exert powerful control over the occurrence and

distribution of other species


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One hypothesis suggests that dominant

species

Are most competitive in exploiting limited

resources

Another hypothesis for dominant speciessuccess

Is that they are most successful at avoiding

predators

Keystone Species


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Keystone Species

Keystone species

Are not necessarily abundant in a community

Exert strong control on a community by their

ecological roles, or niches


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Field studies of sea stars

Exhibit their role as a keystone species in intertidalcommunities

Figure 53.16a,b

(a) The sea star Pisaster ochraceous feeds

preferentially on mussels but will

consume other invertebrates.

With Pisaster(control)

Without Pisaster(experimental)

Num

berofspecies

present

0

5

10

15

20

1963 64 65 66 67 68 69 70 71 72 73

(b) When Pisaster was removed from an intertidal zone,

mussels eventually took over the rock face and eliminated

most other invertebrates and algae. In a control area from

which Pisasterwas not removed, there was little change

in species diversity.


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Observation of sea otter populations and their

predation

Figure 53.17Food chain before

killer whale involve-

ment in chain

(a) Sea otter abundance

(b) Sea urchin biomass

(c) Total kelp density

Numberper

0.25m2

1972 1985 1989 1993 1997

0

2

4

6

8

10

0

100

200

300

400

Gramsper

0.25m2

Otternumber

(%max.count)

0

40

20

60

80

100

Year

Food chain after killer

whales started preying

on otters

Shows the

effect the

otters have

on oceancommunities

Ecosystem Engineers (Foundation Species)


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Ecosystem Engineers (Foundation Species)

Some organisms exert their influence

By causing physical changes in theenvironment that affect community structure


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Beaver dams

Can transform landscapes on a very largescale

Figure 53.18


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Some foundation species act as facilitators

That have positive effects on the survival andreproduction of some of the other species in the

community

Figure 53.19

Salt marsh with Juncus

(foreground)

With

JuncusWithout

Juncus

Numberofplantspecies

0

2

4

6

8

Conditions

Bottom-Up and Top-Down Controls


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Bottom Up and Top Down Controls

The bottom-up model of community

organization

Proposes a unidirectional influence from lower

to higher trophic levels

In this case, the presence or absence of abioticnutrients

Determines community structure, including the

abundance of primary producers


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The top-down model of community

organization

Proposes that control comes from the trophic

level above

In this case, predators control herbivores

Which in turn control primary producers


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Long-term experiment studies have shown

That communities can shift periodically frombottom-up to top-down

Figure 53.20

0 100 200 300 400

Rainfall (mm)

0

25

50

75

100

Percentageof

herb

aceousplantcover


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Pollution

Can affect community dynamics

But through biomanipulation

Polluted communities can be restored

Fish

Zooplankton

Algae

Abundant

Rare

RareAbundant

Abundant

Rare

Polluted State Restored State


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Concept 53.3: Disturbance influences species

diversity and composition

Decades ago, most ecologists favored the

traditional view

That communities are in a state of equilibrium


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However, a recent emphasis on change has

led to a nonequilibrium model

Which describes communities as constantly

changing after being buffeted by disturbances

What Is Disturbance?


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A disturbance

Is an event that changes a community

Removes organisms from a community

Alters resource availability


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Fire

Is a significant disturbance in most terrestrialecosystems

Is often a necessity in some communities

(a) Before a controlled burn.

A prairie that has not burned for

several years has a high propor-

tion of detritus (dead grass).

(b) During the burn. The detritus

serves as fuel for fires.

(c) After the burn. Approximately one

month after the controlled burn,

virtually all of the biomass in this

prairie is living.

Figure 53.21ac


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The intermediate disturbance hypothesis

Suggests that moderate levels of disturbancecan foster higher species diversity than low

levels of disturbance


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The large-scale fire in Yellowstone National

Park in 1988

Demonstrated that communities can often

respond very rapidly to a massive disturbance

Figure 53.22a, b

(a) Soon after fire. As this photo taken soon after the fire shows,

the burn left a patchy landscape. Note the unburned trees in the

distance.

(b) One year after fire. This photo of the same general area taken the

following year indicates how rapidly the community began to

recover. A variety of herbaceous plants, different from those in the

former forest, cover the ground.

Human Disturbance


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Humans

Are the most widespread agents ofdisturbance


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Human disturbance to communities

Usually reduces species diversity

Humans also prevent some naturally occurring

disturbances

Which can be important to community

structure

Ecological Succession


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Ecological succession

Is the sequence of community and ecosystemchanges after a disturbance


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Primary succession

Occurs where no soil exists when successionbegins

Secondary succession

Begins in an area where soil remains after a

disturbance


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Early-arriving species

May facilitate the appearance of later speciesby making the environment more favorable

May inhibit establishment of later species

May tolerate later species but have no impact

on their establishment


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McBride glacier retreating

0 5 10

Miles

Glacier

Bay

Pleasant Is.

Johns Hopkins

Gl.

Reid Gl.

Grand

Pacific Gl.

Canada

Alaska

1940 1912

1899

1879

18791949

1879

1935

1760

1780

1830

1860

1913

1911

18921900

1879

1907 1948

1931

1941

1948

Retreating glaciers

Provide a valuable field-research opportunity onsuccession

Figure 53.23


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Succession on the moraines in Glacier Bay, Alaska

Follows a predictable pattern of change in vegetationand soil characteristics

Figure 53.24ad

(b) Dryasstage

(c) Spruce stage

(d) Nitrogen fixation by Dryas and alder

increases the soil nitrogen content.

Soilnitrogen(g/m2)

Successional stage

Pioneer Dryas Alder Spruce0

10

20

30

40

50

60

(a) Pioneer stage, with fireweed dominant


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Concept 53.4: Biogeographic factors affect

community diversity

Two key factors correlated with a communitys

species diversity

Are its geographic location and its size

Equatorial-Polar Gradients


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The two key factors in equatorial-polar

gradients of species richness

Are probably evolutionary history and climate


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Species richness generally declines along an

equatorial-polar gradient

And is especially great in the tropics

The greater age of tropical environments

May account for the greater species richness


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Climate

Is likely the primary cause of the latitudinalgradient in biodiversity


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The two main climatic factors correlated with

biodiversity

Are solar energy input and water availability

(b) Vertebrates

500 1,000 1,500 2,000

Potential evapotranspiration (mm/yr)

10

50

100

200

Vertebratespeciesrichnes

s

(logscale)

1

100 300 500 700 900 1,100

180

160

140

120

100

80

60

40

20

0

Treespeciesrichness

(a) TreesActual evapotranspiration (mm/yr)

Figure 53.25a, b

Area Effects


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The species-area curve quantifies the idea that

All other factors being equal, the larger thegeographic area of a community, the greater

the number of species


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A species-area curve of North American

breeding birds

Supports this idea

Area (acres)

1 10 100 103 10 4 105 106 107 108 109 1010

N

umberofspecies(logscale)

1

10

100

1,000

Figure 53.26

Island Equilibrium Model


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Species richness on islands

Depends on island size, distance from themainland, immigration, and extinction


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Figure 53.27ac

The equilibrium model of island biogeography

maintains that

Species richness on an ecological island

levels off at some dynamic equilibrium point

Number of species on island

(a) Immigration and extinction rates. The

equilibrium number of species on an

island represents a balance between the

immigration of new species and the

extinction of species already there.

(b) Effect of island size. Large islands may

ultimately have a larger equilibrium num-

ber of species than small islands because

immigration rates tend to be higher and

extinction rates lower on large islands.

Number of species on island Number of species on island

(c) Effect of distance from mainland.

Near islands tend to have larger

equilibrium numbers of species than

far islands because immigration rates

to near islands are higher and extinction

rates lower.

Equilibrium number Small island Large island Far island Near island

Rateofimmigrationorextinction




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Studies of species richness on the Galpagos Islands

Support the prediction that species richnessincreases with island size

The results of the study showed that plant species

richness increased with island size, supporting the species-area theory.

FIELD STUDY

RESULTS

Ecologists Robert MacArthur and E. O. Wilson studied the

number of plant species on the Galpagos Islands, which vary greatly in size, in

relation to the area of each island.

CONCLUSION

200

100

50

25

10

0

Area of island (mi2)

(log scale)

Numbe

rofplantspecies(logscale)

0.1 1 10 100 1,000

5

400

Figure 53.28


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Concept 53.5: Contrasting views of community

structure are the subject of continuing debate

Two different views on community structure

Emerged among ecologists in the 1920s and

1930s

Integrated and Individualistic Hypotheses


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The integrated hypothesis of community

structure

Describes a community as an assemblage of

closely linked species, locked into association

by mandatory biotic interactions


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The individualistic hypothesis of community

structure

Proposes that communities are loosely

organized associations of independently

distributed species with the same abiotic

requirements


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The integrated hypothesis

Predicts that the presence or absence ofparticular species depends on the presence or

absence of other species

Population

densitiesof

individual

species

Environmental gradient

(such as temperature or moisture)

(a) Integrated hypothesis. Communities are discrete groupings

of particular species that are closely interdependent and nearly

always occur together.Figure 53.29a


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The individualistic hypothesis

Predicts that each species is distributedaccording to its tolerance ranges for abiotic

factors

Population

densitiesof

individual

species

Environmental gradient

(such as temperature or moisture)

(b) Individualistic hypothesis. Species are independently

distributed along gradients and a community is simply the

assemblage of species that occupy the same area because of

similar abiotic needs.Figure 53.29b


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In most actual cases the composition of

communities

Seems to change continuously, with each

species more or less independently distributed

Numberof

plants

perhectare

Wet Moisture gradient Dry

(c) Trees in the Santa Catalina Mountains. The distribution of tree species at one

elevation in the Santa Catalina Mountains of Arizona supports the individualistic

hypothesis. Each tree species has an independent distribution along the gradient,

apparently conforming to its tolerance for moisture, and the species that live

together at any point along the gradient have similar physical requirements.

Because the vegetation changes continuously along the gradient, it is impossible to

delimit sharp boundaries for the communities.

0

200

400

600

Figure 53.29c

Rivet and Redundancy Models


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The rivet model of communities

Suggests that all species in a community arelinked together in a tight web of interactions

Also states that the loss of even a single

species has strong repercussions for thecommunity


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The redundancy model of communities

Proposes that if a species is lost from acommunity, other species will fill the gap


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It is important to keep in mind that community

hypotheses and models

Represent extremes, and that most

communities probably lie somewhere in the

middle

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