chapter 53

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

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell & Jane Reece

Lectures by Chris Romero

Chapter 53Chapter 53

comm Ecology


Overview: What Is a comm?

• biological community- pop’s of various spp living close enough for potential interaxn

• Animals & plants surrounding a watering hole in southern Africa are members of a savanna comm


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

• relationships b/w spp in a comm are interspecific interactions

• Interspecific interactions affect spp survival & reproduction

• Ex’s: competition, predation, herbivory, symbiosis (parasitism, mutualism, & commensalism), & disease


Competition

• Interspecific competition- spp compete for a resource in short supply

• Strong competition can lead to competitive exclusion, local elimination of a competing spp


The Competitive Exclusion Principle

• The competitive exclusion principle- 2 spp competing for same limiting resources can’t occupy the same niche


Ecological Niches

• ecological niche- total of a spp’ use of biotic & abiotic resources

• Ecologically similar spp can coexist in a comm if there are 1 or more significant diff's in their niches

• As a result of competition, a spp’ fundamental niche may differ from its realized niche

LE 53-2

Chthamalusfundamental niche

High tide

Low tideOcean

Chthamalusrealized niche

High tide

Low tideOcean

Balanusrealized niche

Chthamalus

Balanus


Resource Partitioning

• Resource partitioning- differentiation of ecological niches, enabling similar spp to coexist in a comm

LE 53-3A. insolitususually percheson shady branches.

A. ricordii

A. insolitus

A. christophei

A. cybotes

A. etheridgei

A. alinigerA. distichus

A. distichusperches onfence posts& othersunnysurfaces.


Character Displacement

• Character displacement- tendency for char’s to be more divergent in sympatric pop's of 2 spp than in allopatric pop's of the same 2 spp

• An example is variation in beak size b/w pop's of 2 spp of Galapagos finches

LE 53-4

Beakdepth

Sympatricpop's

G. fuliginosaG. fortis

Santa María, San Cristóbal

40

20

0

Los Hermanos

40

20

0

Daphne

40

20

0

G. fuliginosa,allopatric

G. fortis,allopatric

Beak depth (mm)

161412108

Pe

rce

nta

ge

of

ind

iv's

in

ea

ch

siz

e c

las

s


Predation

• Predation- 1 spp, (predator), kills & eats the other, the prey

• Some feeding adaptations of predators are claws, teeth, fangs, stingers, & poison


• Prey display various defensive adaptations

• Behavioral defenses include hiding, fleeing, self-defense, & alarm calls

• Animals also have morphological & physiological defense adaptations


• Cryptic coloration/camouflage- makes prey difficult to spot

Video: Seahorse Camouflage


• aposematic coloration- animals w/ effective chem defense often exhibit bright warning coloration

• Predators are particularly cautious in dealing w/ prey that display such coloration


• In some cases, a prey spp may gain significant protection by mimicking the appearance of another spp


• Batesian mimicry- palatable or harmless spp mimics an unpalatable or harmful model

LE 53-7

Hawkmoth larva

Green parrot snake


• Müllerian mimicry- 2 or more unpalatable spp resemble each other

LE 53-8

Cuckoo bee

Yellow jacket


Herbivory

• Herbivory refers to an interaction in which an herbivore eats parts of a plant or alga

• It has led to evolution of plant mechanical & chemical defenses & adaptations by herbivores


Parasitism

• In parasitism, 1 organism, the parasite, derives nourishment from another organism, its host, which is harmed in the process

• Parasitism exerts substantial influence on pop's & the structure of communities


Disease

• Effects of disease on pop's & communities are similar to those of parasites

• Pathogens, disease-causing agents, are typically bacteria, viruses, or protists


Mutualism

• Mutualistic symbiosis, or mutualism, is an interspecific interaction that benefits both spp

Video: Clownfish & Anemone


Commensalism

• In commensalism, 1 spp benefits & the other is apparently unaffected

• Commensal interactions are hard to document in nature because any close association of 2 spp likely affects both


Interspecific Interactions & Adaptation

• Coevolution- reciprocal evolutionary adaptations of 2 interacting spp

• The term is often used too loosely in describing adaptations within a comm

• There is little evidence for true coevolution in most interspecific interactions


Concept 53.2: Dominant & keystone spp exert strong controls on comm structure

• In general, a few spp in a comm exert strong control on that community’s structure

• 2 fundamental features of comm structure are spp diversity & feeding relationships


spp Diversity

• spp diversity of a comm is the variety of organisms that make up the comm

• It has 2 components: spp richness & relative abundance

• spp richness- total # of diff spp in the comm

• Relative abundance- proportion each spp represents of the total indiv's in the comm


• 2 communities can have the same spp richness but a different relative abundance

• A comm w/ an even spp abundance is more diverse than one in which one or 2 spp are abundant & the remainder are rare

LE 53-11

comm 1

AB

C

D

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

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


Trophic Structure

• Trophic structure- feeding relationships b/w organisms in a comm

• It is a key factor in comm dynamics

• Food chains link trophic levels from producers to top carnivores

Video: Shark Eating a Seal

LE 53-12

Quaternaryconsumers

Tertiaryconsumers

Carnivore

Carnivore

Carnivore

Carnivore

Secondaryconsumers

CarnivoreCarnivore

Primaryconsumers

ZooplanktonHerbivore

Primaryproducers

PhytoplanktonPlant

A terrestrial food chain A marine food chain


Food Webs

• food web- branching food chain w/ complex trophic interactions

LE 53-13

Euphausids(krill)

Carnivorousplankton

Phyto-plankton

Copepods

Squids

Elephantseals

FishesBirds

Crab-eaterseals

Leopardseals

Spermwhales

Smallertoothedwhales

Baleenwhales

Humans


• Food webs can be simplified by isolating a portion of a comm that interacts very little w/ the rest of the comm

LE 53-14

Zooplankton

Fish larvae

Fish eggs

Sea nettle Juvenile striped bass


Limits on Food Chain Length

• Each food chain in a food web is usually only a few links long

• 2 hypotheses attempt to explain food chain length: the energetic hypothesis & the dynamic stability hypothesis


• The energetic hypothesis suggests that length is limited by inefficient energy transfer

• The dynamic stability hypothesis proposes that long food chains are less stable than short ones

• Most data support the energetic hypothesis

LE 53-15

Productivity

# o

f tr

op

hic

lin

ks

# o

f sp

p

No. of trophiclinks

No. of spp

High(control)

6

5

4

3

2

1

0

6

5

4

3

2

1

0Medium Low


spp w/ a Large Impact

• Certain spp have a very large impact on comm structure

• Such spp are highly abundant or play a pivotal role in comm dynamics


Dominant spp

• Dominant spp- most abundant or have the highest biomass

• They exert powerful control over the occurrence & distribution of other spp


• One hypothesis suggests that dominant spp are most competitive in exploiting resources

• Another hypothesis is that they are most successful at avoiding predators


Keystone spp

• In contrast to dominant spp,

• keystone spp- not necessarily abundant in a comm but exert strong control on a comm by their ecological roles, or niches


• Field studies of sea stars exhibit their role as a keystone spp in intertidal communities

LE 53-16

Without Pisaster (experimental)

w/ Pisaster (control)

1963 ’64 ’65 ’66 ’67 ’68 ’69 ’70 ’71 ’72 ’73

20

15

10

5

0

# o

f s

pp

pre

se

nt


• Observation of sea otter pop's & their predation shows how otters affect ocean communities

LE 53-17

100

80

60

40

0

20

Sea otter abundance

Ott

er

#(%

ma

x.

co

un

t)

400

300

200

0

100

Sea urchin biomass

Gra

ms

pe

r0

.25

m2

10864

02

Total kelp density

# p

er

0.2

5 m

2

19971993198919851972Year

Food chain beforekiller whaleinvolvement inchain

Food chain afterkiller whales startedpreying on otters


Ecosystem “Engineers” (Foundation spp)

• Some organisms exert influence by causing physical changes in the environment that affect comm structure

• For example, beaver dams can transform landscapes on a very large scale


• Some foundation spp act as facilitators that have positive effects on survival & reproduction of some other spp in the comm

LE 53-19

# o

f p

lan

t sp

p

8

6

4

0

2

Conditions

w/Juncus

WithoutJuncusSalt marsh w/ Juncus

(foreground)


Bottom-Up & Top-Down Controls

• The bottom-up model of comm organization proposes a unidirectional influence from lower to higher trophic levels

• In this case, presence or absence of mineral nutrients determines comm structure, including abundance of primary producers


• The top-down model proposes that control comes from the trophic level above

• In this case, predators control herbivores, which in turn control primary producers


• Long-term experimental studies have shown that communities can shift periodically from bottom-up to top-down controls

LE 53-20

Per

cen

tag

e o

fh

erb

aceo

us

pla

nt

cove

r100

75

50

0

25

Rainfall (mm)

200 300 4000 100


• Pollution can affect comm dynamics

• Biomanipulation can help restore polluted communities

LE 53-UN1171

Polluted State Restored State

Fish Abundant Rare

Zooplankton AbundantRare

Algae Abundant Rare


Concept 53.3: Disturbance influences spp diversity & composition

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

• Recent evidence of change has led to a nonequilibrium model, which describes communities as constantly changing after being buffeted by disturbances


What Is Disturbance?

• disturbance- event that changes a comm, removes organisms from it, & alters resource availability

• Fire is a significant disturbance in most terrestrial ecosystems

• It is often a necessity in some communities

LE 53-21

Before a controlled burn.A prairie that has not burned for several years has a high propor-tion of detritus (dead grass).

During the burn. The detritus serves as fuel for fires.

After the burn. Approximately one month after the controlled burn, virtually all of the biomass in this prairie is living.


• intermediate disturbance hypothesis- moderate levels of disturbance can foster higher 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

LE 53-22

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.

One year after fire. This photo of the same general area taken the following year indicates how rapidly the com-munity 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 spp diversity

• Humans also prevent some naturally occurring disturbances, which can be important to comm structure


Ecological Succession

• Ecological succession- seq of comm & ecosystem changes after a disturbance

• Primary succession- no soil exists/bare land

• Secondary succession- area still w/soil after a disturbance


• Early-arriving spp & later-arriving spp may be linked in 1 of 3 processes:

– Early arrivals may facilitate appearance of later spp by making the environment favorable

– They may inhibit establishment of later spp

– They may tolerate later spp but have no impact on their establishment


• Retreating glaciers provide a valuable field-research opportunity for observing succession

LE 53-23

McBride glacier retreating

Canada

Alaska

1940

1941

1931 1911

19481912

1907

1879 1879

1879

1899

1948

GrandPacific Gl.

1900

1935 194919131892

Riggs G

l.

Muir G

l.

Plateau Gl.

McB

ride

Gl.

Cas

emen

t Gl.

1860

Johns HopkinsGl.

Pleasant Is.

Reid Gl.1879

GlacierBay

1760

1830

1780

Miles

15Kilometers

10

105

5

0

0


• Succession on the moraines in Glacier Bay, Alaska, follows a predictable pattern of change in vegetation & soil characteristics

LE 53-24Pioneer stage, w/ fireweed dominant

Dryas stage

Spruce stageNitrogen fixation by Dryas & alder

increases the soil nitrogen content.

Successional stage

DryasPioneer Alder Spruce

So

il n

itro

gen

(g

/m2)

60

50

40

30

20

10

0


Concept 53.4: Biogeographic factors affect comm diversity

• 2 key factors correlated w/ a community’s spp diversity are geographic location & size


Equatorial-Polar Gradients

• 2 key factors in equatorial-polar gradients of spp richness are probably evolutionary history & climate

• spp richness generally declines along an equatorial-polar gradient & is especially great in the tropics

• The greater age of tropical environments may account for the greater spp richness


• Climate is likely the primary cause of the latitudinal gradient in biodiversity

• 2 main climatic factors correlated w/ biodiversity: sun & water

• They can be considered together by measuring a community’s rate of evapotranspiration

• Evapotranspiration is evaporation of water from soil plus transpiration of water from plants

LE 53-25

Trees

Tre

e sp

p r

ich

nes

s

180

160

140

120

100

80

0

Ver

teb

rate

sp

p r

ich

nes

s(l

og

sca

le)

200

100

50

10

60

40

20

1,100900700500300100Actual evapotranspiration (mm/yr)

Vertebrates

2,000Potential evapotranspiration (mm/yr)

1,5001,000500


Area Effects

• The species-area curve quantifies the idea that, all other factors being equal, a larger geographic area has more spp

• A species-area curve of North American breeding birds supports this idea

LE 53-26

# o

f sp

p (

log

sca

le)

1,000

Area (acres)

1010109106 107 108103 104 1051 10 100

100

10

1


Island Equilibrium Model

• spp richness on islands depends on island size, distance from the mainland, immigration, & extinction

• The equilibrium model of island biogeography maintains that spp richness on an ecological island levels off at a dynamic equilibrium point

LE 53-27

Immigration & extinction rates

# of spp on island

Equilibrium#

Imm

igration

Rat

e o

f im

mig

rati

on

or

exti

nct

ion

Extin

ctio

n

Effect of island size

# of spp on island

Smallisland

Imm

igration

Rat

e o

f im

mig

rati

on

or

exti

nct

ion

Extin

ctio

n

Largeisland

(large island)

Imm

igration

(small island)

Extin

ctio

n

(larg

e is

land)

(sm

all i

slan

d)

Effect of distance from mainland

# of spp on island

Farisland

Imm

igration

Rat

e o

f im

mig

rati

on

or

exti

nct

ion

Extin

ctio

n

Nearisland

(near island)

Imm

igration

(far island) Extinctio

n

(near i

sland)

(far i

slan

d)


• Studies of spp richness on the Galápagos Islands support the prediction that spp richness increases w/ island size

LE 53-28

Area of island (mi2)(log scale)

400#

of

pla

nt

spp

(lo

g s

cale

)

1,0001001010.1

200

100

50

25

10

5


Concept 53.5: Contrasting views of comm structure are the subject of continuing debate

• In the 1920s & 1930s, 2 views on comm structure emerged: the integrated hypothesis & the individualistic hypothesis


Integrated & Individualistic Hypotheses

• integrated hypothesis- describes a comm as an assemblage of closely linked spp, locked into association by mandatory biotic interactions

• individualistic hypothesis- communities are loosely organized associations of independently distributed spp w/ the same abiotic requirements


• The integrated hypothesis predicts that presence or absence of particular spp depends on presence or absence of other spp

LE 53-29a

Environmental gradient(such as temperature or moisture)

po

pd

ensi

ties

of

ind

ivsp

p

Integrated hypothesis


• The individualistic hypothesis predicts that each spp is distributed according to its tolerance ranges for abiotic factors

LE 53-29b

Environmental gradient(such as temperature or moisture)

po

pd

ensi

ties

of

ind

ivsp

p

Individualistic hypothesis


• In most actual cases, composition of communities seems to change continuously, w/ each spp more or less independently distributed

LE 53-29c

Trees in the Santa Catalina Mountains

# o

fp

lan

tsp

er h

ecta

re

Moisture gradientWet

600

400

200

0

Dry


Rivet & Redundancy Models

• The rivet model suggests that all spp in a comm are linked in a tight web of interactions

• It also states that loss of even a single spp has strong repercussions for the comm

• The redundancy model proposes that if a spp is lost, other spp will fill the gap

• comm hypotheses & models represent extremes; most communities probably lie somewhere in the middle

chapter 53

Documents