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right © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 53 Community Ecology

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Chapter 53. Community Ecology. Overview: What Is a Community? A biological community Is an assemblage of populations of various species living close enough for potential interaction. Figure 53.1. The various animals and plants surrounding this watering hole - PowerPoint PPT Presentation

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Page 1: Chapter 53

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 53Chapter 53

Community Ecology

Page 2: Chapter 53

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• Overview: What Is a Community?

• A biological community

– Is an assemblage of populations of various species living close enough for potential interaction

Page 3: Chapter 53

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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

Page 4: Chapter 53

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• Concept 53.1: A community’s 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

Page 5: Chapter 53

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• Interspecific interactions

– Can have differing effects on the populations involved

Table 53.1

Page 6: Chapter 53

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Competition

• Interspecific competition

– Occurs when species compete for a particular resource that is in short supply

• Strong competition can lead to competitive exclusion

– The local elimination of one of the two competing species

Page 7: Chapter 53

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The Competitive Exclusion Principle

• The competitive exclusion principle

– States that two species competing for the same limiting resources cannot coexist in the same place

Page 8: Chapter 53

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Ecological Niches

• The ecological niche

– Is the total of an organism’s use of the biotic and abiotic resources in its environment

Page 9: Chapter 53

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• The niche concept allows restatement of the competitive exclusion principle

– Two species cannot coexist in a community if their niches are identical

Page 10: Chapter 53

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• 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 Chthamalus population spread into that area.

The spread of Chthamalus when Balanus was removed indicates that competitive exclusion makes the realizedniche of Chthamalus much smaller than its fundamental niche.

RESULTS

CONCLUSION

Ocean

Ecologist Joseph Connell studied two barnacle speciesBalanus balanoides and Chthamalus stellatus that have a stratified distribution on rocks along the coast of Scotland.

EXPERIMENT

In nature, Balanus fails to survive high on the rocks because it isunable to resist desiccation (drying out) during low tides. Its realized niche is therefore similar to its fundamental niche. In contrast, Chthamalus is usually concentrated on the upper strata of rocks. To determine the fundamental of niche of Chthamalus, Connell removed Balanus from the lower strata.

Low tide

High tide

Chthamalusfundamental niche

Chthamalusrealized niche

Low tide

High tideChthamalus

Balanusrealized niche

Balanus

Ocean

Figure 53.2

Page 11: Chapter 53

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• As a result of competition

– A species’ fundamental niche may be different from its realized niche

Page 12: Chapter 53

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A. insolitususually percheson shady branches.

A. distichus perches on fence posts and

other sunny surfaces.

A. distichus

A. ricordii

A. insolitus

A. christophei

A. cybotes

A. etheridgei

A. alinigar

Figure 53.3

Resource Partitioning

• Resource partitioning is the differentiation of niches

– That enables similar species to coexist in a community

Page 13: Chapter 53

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G. fortis

Beak depth (mm)

G. fuliginosa

Beak depth

Los Hermanos

Daphne

Santa María, San Cristóbal

Sympatric populations

G. fuliginosa, allopatric

G. fortis, allopatric

Per

cent

ages

of

indi

vidu

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in e

ach

size

cla

ss

40

20

0

40

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40

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8 10 12 14 16

Figure 53.4

Character Displacement

• In character displacement

– There is a tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species

Page 14: Chapter 53

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Predation

• Predation refers to an interaction

– Where one species, the predator, kills and eats the other, the prey

Page 15: Chapter 53

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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 mimicking the appearance of another

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• In Batesian mimicry

– A palatable or harmless species mimics an unpalatable or harmful model

(a) Hawkmoth larva

(b) Green parrot snake

Figure 53.7a, b

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• In Müllerian mimicry

– Two or more unpalatable species resemble each other

(a) Cuckoo bee

(b) Yellow jacketFigure 53.8a, b

Page 21: Chapter 53

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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 another organism, 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

Page 26: Chapter 53

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Mutualism

• Mutualistic symbiosis, or mutualism

– Is an interspecific interaction that benefits both species

Figure 53.9

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Commensalism

• In commensalism

– One species benefits and the other is not affected

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

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Interspecific Interactions and Adaptation

• Evidence for coevolution

– Which involves reciprocal genetic change by interacting 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 community’s structure

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Species Diversity

• The species diversity of a community

– Is the variety of different kinds of organisms that make up the community

– Has two components

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• Species richness

– Is the total number of different species in the community

• 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 a different relative abundance

Community 1A: 25% B: 25% C: 25% D: 25%

Community 2A: 80% B: 5% C: 5% D: 10%

D

C

BA

Figure 53.11

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• A community with an even species abundance

– Is more diverse than one in which one or two species are abundant and the remainder rare

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Trophic Structure

• Trophic structure

– Is the feeding relationships between organisms in 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 trophic levels from producers to top carnivores

Page 38: Chapter 53

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Food Webs

• A food web Humans

Baleen whales

Crab-eater seals

Birds Fishes Squids

Leopardseals

Elephant seals

Smaller toothed whales

Sperm whales

Carnivorous plankton

Euphausids (krill)

Copepods

Phyto-plankton

Figure 53.13

– Is a branching food chain with complex trophic interactions

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• Food webs can be simplified

– By isolating a portion of a community that interacts very little with the rest of the community

Sea nettle

Fish larvae

ZooplanktonFish eggs

Juvenile striped bass

Figure 53.14

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Limits 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 stable than 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

Num

ber

of

spec

ies

Num

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of

trop

hic

links

0

1

2

3

4

5

6

0

1

2

3

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5

6

Figure 53.15

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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

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Dominant Species

• Dominant species

– Are those species in a community that are most 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 species success

– Is that they are most successful at avoiding predators

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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 intertidal communities

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

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of s

peci

es

pres

ent

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 Pisaster was 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 beforekiller whale involve-ment in chain

(a) Sea otter abundance

(b) Sea urchin biomass

(c) Total kelp density

Num

ber

per

0.25

m2

1972 1985 1989 1993 19970

2

468

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Gra

ms

per

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Ott

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umbe

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max

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unt)

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80

100

Year

Food chain after killerwhales started preyingon otters

– Shows the effect the otters haveon ocean communities

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Ecosystem “Engineers” (Foundation Species)

• Some organisms exert their influence

– By causing physical changes in the environment that affect community structure

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• Beaver dams

– Can transform landscapes on a very large scale

Figure 53.18

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• Some foundation species act as facilitators

– That have positive effects on the survival and reproduction of some of the other species in the community

Figure 53.19

Salt marsh with Juncus (foreground)

With Juncus

Without Juncus

Nu

mb

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of

pla

nt

spe

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s

0

2

4

6

8

Conditions

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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 abiotic nutrients

– 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 from bottom-up to top-down

Figure 53.20

0 100 200 300 400

Rainfall (mm)

0

25

50

75

100

Per

cen

tag

e o

f he

rbac

eous

pla

nt c

over

Page 56: Chapter 53

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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

Page 57: Chapter 53

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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

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What Is Disturbance?

• 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 terrestrial ecosystems

– Is often a necessity in some communities

(a) Before a controlled burn.A prairie that has not burned forseveral 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 53.21a–c

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• The intermediate disturbance hypothesis

– Suggests that moderate levels of disturbance can 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.

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Human Disturbance

• Humans

– Are the most widespread agents of disturbance

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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

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Ecological Succession

• Ecological succession

– Is the sequence of community and ecosystem changes after a disturbance

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• Primary succession

– Occurs where no soil exists when succession begins

• 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 species by 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

GlacierBay

Pleasant Is.

Johns HopkinsGl.

Reid Gl.

GrandPacific Gl.

Canada

Alaska

1940 1912

1899

1879

18791949

1879

1935

1760

17801830

1860

1913

1911

18921900

1879

1907 19481931

1941

1948

Cas

emen

t Gl.

McB

ride

Gl.

Plateau Gl.

Muir G

l.

Riggs G

l.

• Retreating glaciers

– Provide a valuable field-research opportunity on succession

Figure 53.23

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• Succession on the moraines in Glacier Bay, Alaska

– Follows a predictable pattern of change in vegetation and soil characteristics

Figure 53.24a–d

(b) Dryas stage

(c) Spruce stage

(d) Nitrogen fixation by Dryas and alder increases the soil nitrogen content.

Soi

l nitr

ogen

(g/

m2)

Successional stagePioneer Dryas Alder Spruce

0

10

20

30

40

50

60

(a) Pioneer stage, with fireweed dominant

Page 70: Chapter 53

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• Concept 53.4: Biogeographic factors affect community diversity

• Two key factors correlated with a community’s species diversity

– Are its geographic location and its size

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Equatorial-Polar Gradients

• 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 latitudinal gradient 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

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tebr

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spec

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richn

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(log

scal

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0

Tre

e sp

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s

(a) TreesActual evapotranspiration (mm/yr)

Figure 53.25a, b

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Area Effects

• The species-area curve quantifies the idea that

– All other factors being equal, the larger the geographic 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 10 100 103 104 105 106 107 108 109 1010

Nu

mb

er

of

spe

cie

s (lo

g s

cale

)

1

10

100

1,000

Figure 53.26

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Island Equilibrium Model

• Species richness on islands

– Depends on island size, distance from the mainland, immigration, and extinction

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Figure 53.27a–c

• 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 anisland represents a balance between the immigration of new species and theextinction 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 largerequilibrium numbers of species thanfar islands because immigration ratesto near islands are higher and extinctionrates lower.

Equilibrium number Small island Large island Far island Near island

Imm

igration

Extin

ctio

n

Extin

ctio

n

Imm

igration

Extin

ctio

n

Imm

igration

(small island)

(larg

e is

land)

(large island)

(sm

all

isla

nd) Imm

igration

Extin

ctio

n

Imm

igration

(far island)

(near i

sland)

(near island) (far i

slan

d)

Extinctio

n

Rat

e of

imm

igra

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or e

xtin

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Rat

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imm

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tion

or e

xtin

ctio

n

Rat

e of

imm

igra

tion

or e

xtin

ctio

n

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• Studies of species richness on the Galápagos Islands

– Support the prediction that species richness increases 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 Galápagos 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)

Num

ber

of p

lant

spe

cies

(lo

g sc

ale)

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

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Integrated and Individualistic Hypotheses

• 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 of particular species depends on the presence or absence of other species

Pop

ulat

ion

dens

ities

of

indi

vidu

al

spec

ies

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 distributed according to its tolerance ranges for abiotic factors

Pop

ulat

ion

dens

ities

of

indi

vidu

al

spec

ies

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

Num

ber

of

plan

tspe

r he

ctar

e

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

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Rivet and Redundancy Models

• The rivet model of communities

– Suggests that all species in a community are linked together in a tight web of interactions

– Also states that the loss of even a single species has strong repercussions for the community

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• The redundancy model of communities

– Proposes that if a species is lost from a community, 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