Chapter 53 (pgs. 1174 – 1196) Community Ecology AP minknow The difference between a fundamental niche and a realized niche The role of competitive exclusion.

Chapter 53 (pgs. 1174 – 1196) Community Ecology

AP minknow•The difference between a fundamental niche and a realized niche•The role of competitive exclusion in interspecific competition.•The symbiotic relationships of parasitism, mutualism, and commensalism.•The impact of keystone species on community structure.•The difference between primary and secondary succession.

What Is a Community?•  1.Explain the relationship between species richness and relative

abundance. • 2.Define and compare the individualistic hypothesis of H.A. Gleason

and the interactive hypothesis of F.E. Clements with respect to communities.

• Interspecific Interactions and Community Structure• 3.List four possible specific interactions and explain how the

relationships affect the population densities of the two species. • 4.Explain how interspecific competition may affect community

structure. • 5.Describe the competitive exclusion principle and explain how

competitive exclusion may affect community structure. • 6.Define an ecological niche and restate the competitive exclusion

principle using the niche concept. • 7.Explain how resource partitioning can affect species diversity. • 8.Define and compare predation, herbivory, and parasitism. • 9.Relate some specific predatory adaptations to the properties of

the prey. • 10.Describe the defense mechanisms that evolved in plants to

reduce predation by herbivores. 

• 11.Explain how cryptic coloration and warning coloration aid an animal in avoiding predators. 

• 12.Distinguish between Batesian mimicry and Müllerian mimicry. 

• 13.Describe how predators use mimicry to obtain prey. • 14.Distinguish among endoparasites, ectoparasites, and

pathogens. • 15.Distinguish among parasitism, mutualism, and

commensalism. • 16.Distinguish between a food chain and a food web. Describe

the factors that transform food chains into food webs. • 17.Describe two ways to simplify food webs. • 18.Summarize two hypotheses that explain why food chains

are relatively short. • 19.Explain how dominant and keystone species exert strong

control on community structure. Give several examples of each. 

• 20.Describe and distinguish between the bottom-up and top-down models of community organization. Also describe some models that are intermediate between those two extremes.

• Disturbance and Community Structure• 21.Describe how disturbances affect community structure and

composition. Illustrate this point with several well-studied examples. 

• 22.Give examples of humans as widespread agents of disturbance. 

• 23.Describe and distinguish between primary and secondary succession. 

• 24.Describe and distinguish among facilitation, inhibition, and toleration. 

• 25.Describe the process and pattern of succession on moraines in Glacier Bay.

• Biogeographic Factors Affecting the Biodiversity of Communities

• 26.Describe and distinguish between species richness and relative abundance. 

• 27.Describe the data necessary to measure biodiversity. • 28.Describe and explain how species richness varies along

the equatorial-polar gradient. • 29.Define the species-area curve. • 30.Explain how species richness on islands varies according

to island size and distance from the mainland.

What Is a Community?• A biological

community– Is an

assemblage of populations of various species living close enough for potential interaction

•The various animals and plants surrounding this watering hole

•Are all members of a savanna community in southern Africa

• Populations are linked by interspecific interactions– That affect the

survival and reproduction of the species engaged in the interaction

– These interaction can have differing effects on the populations involved

53.1: A community’s interactions include competition, predation, herbivory, symbiosis, and disease

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

The Competitive Exclusion PrincipleThe competitive exclusion principle

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

Click on picture to watch movie

Ecological Niches• Habitat - the area where an

organism lives, including the biotic and abiotic factors that affect the organism.

• Resources - any necessity of life, such as water, nutrients, light, food, or space.

Habitat + Resources = ?????

• The ecological niche– Is the total of an organism’s use of

the biotic and abiotic resources in its environment

Warbler Niches

• Can you have two separate organisms occupying the same exact niche???

NO•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

As a result of competition

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

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 tide

Chthamalus

Balanusrealized niche

Balanus

Ocean

A. insolitususually percheson shady branches.

A. distichus perches on fence posts

and other sunny

surfaces.

A. distichus

A. ricordii

A. insolitusA. christophei

A. cybotesA. etheridgei

A. alinigar

Resource Partitioning• 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 María, San Cristóbal

Sympatric populations

G. fuliginosa, allopatric

G. fortis, allopatric

Per

cent

ages

of

indi

vidu

als

in e

ach

size

cla

ss

40

20

0

40

20

0

40

20

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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

– Sympatric population – geographically overlapping

– Allopatric population – geographically isolated

Predation• Predation refers

to an interaction– Where one

species, the predator, kills and eats the other, the prey

•Feeding adaptations of predators include

•Claws, teeth, fangs, stingers, and poison

•Animals also display•A great variety of defensive adaptations

Defensive Adaptations

• Cryptic coloration

• Aposematic coloration

• Batesian mimicry

• Mullerian mimicry

Cryptic coloration, or camouflage

Makes prey difficult to spot

Figure 53.5

Aposematic coloration– Warns predators to stay away from prey – Poison arrow frog

Figure 53.6

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

In Müllerian mimicry

Two or more unpalatable species resemble each other

(a) Cuckoo bee

(b) Yellow jacketFigure 53.8a, b

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

Community Interactions

• Symbiosis – any relationship in which two species live closely together.

– There are three types of Symbiosis• Parasitism

– Disease

• Mutualism• Commensalism

Parasitism• In parasitism, one organism, the parasite

– Derives its nourishment from another organism, its host, which is harmed in the process

Parasitism

• Parasitism exerts substantial influence on populations– And the

structure of communities

– Parasite– Host

• Endoparasites• Ectoparasites• Parasitoidism

Disease

• The effects of disease on populations and communities– Is similar to that of parasites

Pathogens, disease-causing agents

Are typically bacteria, viruses, or protists

Mutualism• Mutualistic symbiosis, or mutualism

– Is an interspecific interaction that benefits both species

Figure 53.9

Commensalism• In commensalism

– One species benefits and the other is not affected

• Commensal interactions have been difficult to document in nature– Because any close

association between species likely affects both species Figure 53.10

Interspecific Interactions and Adaptation

• Evidence for coevolution– Which involves reciprocal genetic change by

interacting populations, is scarce

•However, generalized adaptation of organisms to other organisms in their environment

•Is a fundamental feature of life

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

• Dominant Species – Those species in a community that have the highest abundance or highest biomass. These species exert a powerful control over the occurrence and distribution of other species.

• Keystone Species – A species that is not necessarily abundant in a community yet exerts strong control on community structure by the nature of its ecological role or niche

Species Diversity• The species diversity

of a community– Is the variety of

different kinds of organisms that make up the community

– Has two components

• 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

Species Diversity• Two different communities

– Can have the same species richness, but a different relative abundance

Community 1

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

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

D

C

B

A

Figure 53.11

A community with an even species abundance

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

Trophic Structure

• Trophic structure – Is the feeding relationships between organisms

in a community– Is a key factor in community dynamics

• We can look at trophic structure through– Food Chains– Food Webs

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

– Help to show the flow of energy through an ecosystem

Food WebsHumans

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

Food Webs

• 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

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

•The energetic hypothesis

•suggests that the length of a food chain Is limited by the inefficiency of energy transfer along the chain

•The dynamic stability hypothesis

•Proposes that long food chains are less stable than short ones

Limits on Food Chain Lengths• 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

ber

of

trop

hic

links

0

1

2

3

4

5

6

0

1

2

3

4

5

6

Figure 53.15

Reduction of energy input in a tree-hole community (Queensland, Australia) had a direct affect on the length of the food chain

Species with a Large Impact

• Certain species have an especially large impact on the structure of entire communities– Either because they are highly abundant r because

they play a pivotal role in community dynamics

• Dominant Species

• Keystone Species

Dominant Species• 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

Keystone Species• Field studies of sea

stars– Exhibit their role as a keystone

species in intertidal communities

(a) The sea star Pisaster ochraceous feeds preferentially on mussels but will consume other invertebrates.

With Pisaster (control)

Without Pisaster (experimental)

Num

ber

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.

Keystone Species

Figure 53.17 Food 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

10

0

100

200

300

400

Gra

ms

per

0.25

m2

Ott

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umbe

r (%

max

. co

unt)

0

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20

60

80

100

YearFood chain after killerwhales started preyingon otters

– Shows the effect the otters haveon ocean communities

• Observation of sea otter populations and their predation

Ecosystem “Engineers” (Foundation Species)

• Some organisms exert their influence– By causing physical changes in the

environment that affect community structure

Foundation Species• Some

foundation species act as facilitators– That have

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

Salt marsh with Juncus (foreground)

With Juncus

Without Juncus

Nu

mb

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of

pla

nt

spe

cie

s

0

2

4

6

8

Conditions

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

Bottom-Up and Top-Down Controls

• 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

Long-term experiment studies have shown

That communities can shift periodically from bottom-up to top-down

0 100 200 300 400

Rainfall (mm)

0

25

50

75

100

Per

cen

tag

e o

f he

rbac

eous

pla

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over

Bottom-Up

Top-Down

Rainfall determines community controls in this Chilean desert comm.

(Non-El Nino) Dry

(El Nino) Wet

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

53.3: Disturbance influences species diversity and composition

• Decades ago, most ecologists favored the traditional view– That communities are in a state of equilibrium

• 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?• A disturbance

– Is an event that changes a community

– Removes organisms from a community

– Alters resource availability

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.

•The intermediate disturbance hypothesis•Suggests that moderate levels of disturbance can foster higher species diversity than low levels of disturbance

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

• Humans– Are the most widespread

agents of disturbance

• Human disturbance to communities– Usually reduces species

diversity

• Humans also prevent some naturally occurring disturbances– Which can be important to

community structure

Ecological Succession

• Ecosystems are constantly in flux.

Ecological Succession – is the series of predictable changes that occurs in an ecosystem over time.

• Primary succession

• Secondary succession

Primary Succession• Occurs on surfaces

where no soil exists, usually after a volcanic eruption. (receding glaciers)– 1. Bare rock community is

populated by an pioneer species (first species to populate an area). Usually lichens (fungus and alga).

– 2. Pioneer species help to form soil and puts nutrients into soil.

– 3. Plants begin to grow then off to the races

Secondary Succession• Occurs in an community where everything has been

removed but the soil.• What could cause the process of primary succession to

begin?

Succession on the moraines in Glacier Bay, Alaska

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

(b) Dryas stage

(c) Spruce stage(d) Nitrogen fixation by

Dryas and alder increases the soil nitrogen content.

So

il n

itro

ge

n

(g/m

2)

Successional stagePioneer Dryas Alder Spruce

0

10

20

30

40

50

60

(a) Pioneer stage, with fireweed dominant

Further Your Information

• Read 53.4 and 53.5 Page 1175 Page 1180