53 community ecology - WordPress.com · Community Ecology Copyright © 2005 Pearson Education, Inc....

1

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


Community– Populations of various species living close

enough for potential interaction

Figure 53.1

Savanna community –which species are members?


Definitions:

• Studies examining the interaction between organisms at a particular site or in a specific area.

• The study of the distribution, abundance, and interactions between populations of coexisting species.

Examples:

Food webs, Species diversity, Succession, Invasion biology, Restoration ecology

What is Community Ecology?


What is Community Ecology ?


Interactions

• Competition

• Predation

• Herbivory

• Symbiosis

• Disease


Interspecific interactions

Table 53.1

2


Competition

• Interspecific

– When species compete for a resource in short supply (limited)

• Can lead to competitive exclusion

– Local elimination of one of the species


The Competitive Exclusion Principle– Two species competing for the same limiting

resources cannot coexist in the same place (cannot occupy the same niche)


Ecological Niches

– Total of an organism’s use of biotic and abioticresources

– Habitat: organism’s address

– Niche: its profession


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

• Ecologically similar species can coexist in a community

– If a difference in niches

When Connell removed Balanus from the lower strata, the Chthamalus population spread into that area.

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

RESULTS

CONCLUSION

Ocean

Ecologist Joseph Connell studied two barnacle species⎯Balanus 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

3


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

Resource Partitioning


G. fortis

Beak depth (mm)

G. fuliginosa

Beak depth

Los Hermanos

Daphne

Santa María, San Cristóbal

Sympatric populations

G. fuliginosa, allopatric

G. fortis, allopatric

Perc

enta

ges

of in

divi

dual

s in

eac

h si

ze c

lass

40

20

0

40

20

0

40

20

0

8 10 12 14 16

Figure 53.4

Character Displacement– Characteristics more divergent in sympatric

populations of two species than in allopatricpopulations of the same two species


Predation•One species kills & eats the other



Predators feeding adaptations– Claws, teeth, fangs, stingers, and poison

4


Prey – defense mechanisms

• Cryptic coloration

Figure 53.5Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Aposematic coloration

• Warns predators

Figure 53.6


Batesian mimicry– A harmless species mimics a harmful one

(a) Hawkmoth larva

(b) Green parrot snake


Müllerian mimicry

• Two or more unpalatable species resemble each other

(a) Cuckoo bee

(b) Yellow jacketFigure 53.8a, b


Herbivory– Has led to evolution of plant mechanical and

chemical defenses and consequent adaptations by herbivores


Parasitism•Parasite feeds on host, which is harmed

5


Disease

• Pathogens, disease-causing agents

– bacteria, viruses, or protists


Mutualism– interspecific interaction that benefits both species


Commensalism•One species benefits, the other not affected


Interspecific Interactions and Adaptation

• Evidence for coevolution

– reciprocal genetic change by interacting populations, is scarce

– But organisms adapt to biota


Keystone species

6


Species diversity

• Species richness

– Total number of different species in the community

• Relative abundance

– Proportion each species represents of the total individuals in the community


• 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


• 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– Feeding relationships between organisms

– Key factor in community dynamics


• Food chainsQuaternary consumers

Tertiary consumers

Secondary consumers

Primary consumers

Primary producers

Carnivore

Carnivore

Carnivore

Herbivore

Plant

Carnivore

Carnivore

Carnivore

Zooplankton

PhytoplanktonA terrestrial food chain A marine food chainFigure 53.12

– Link the trophiclevels from producers to top carnivores


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

– A branching food chain with complex trophicinteractions

7


• Food webs can be simplified

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

• Two hypotheses

– attempt to explain food chain length


Energetic hypothesis– Food chain length limited by inefficiency of

energy transfer


Dynamic stability– long food chains are less stable than short

ones


• Most data

– Support the energetic hypothesis

High (control)

Medium Low

Productivity

No. of species

No. of trophiclinks

Num

ber o

f spe

cies

Num

ber o

f tro

phic

links

0

1

2

3

4

5

6

0

1

2

3

4

5

6


Dominant Species

• Dominant species

– most abundant or have highest biomass

– powerful control over presence and distribution of other species

8


Keystone Species

• Keystone species

– Are not necessarily abundant in a community

– Exert strong control on a community by their ecological roles, or niches

– Either most competitive or,

– Best at avoiding predation


Sea stars

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

ber o

f spe

cies

pr

esen

t

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.


Sea otters

Figure 53.17Food chain beforekiller whale involve-ment in chain

(a) Sea otter abundance

(b) Sea urchin biomass

(c) Total kelp density

Num

ber p

er

0.25

m2

1972 1985 1989 1993 199702468

10

0

100

200

300

400

Gra

ms

per

0.25

m2

Otte

r num

ber

(% m

ax. c

ount

)

0

40

20

60

80

100

Year

Food chain after killerwhales started preyingon otters

– Shows the effect the otters haveon ocean communities


Ecosystem “Engineers” (Foundation Species)

• Some organisms exert their influence

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


• Beaver dams

– Can transform landscapes on a very large scale


• Some foundation species act as facilitators

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

Figure 53.19Salt marsh with Juncus(foreground)

With Juncus

Without Juncus

Num

ber o

f pla

nt s

peci

es

0

2

4

6

8

Conditions

9


Bottom-Up and Top-Down Controls

Bottom up

• influence from lower to higher trophic levels

• abiotic nutrients

Top-down

• control from the trophic level above

• predators control herbivores


• 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

cent

age

of

herb

aceo

us p

lant

cov

er


• 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


What Is Disturbance?– event that changes a community

– removes organisms

– alters resource availability


• Fire

– significant

– often a necessity

(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 detritusserves 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


intermediate disturbance hypothesis

• moderate levels of disturbance fosters higher species diversity

10


Human Disturbance

• Introductions

• Land clearing


Ecological Succession– sequence of community and ecosystem

changes after a disturbance


• Primary succession

– Occurs where no soil exists

• Secondary succession

– Soil present


• Early-arriving species

– May facilitate later species

– May inhibit later species

– May tolerate later species


McBride glacier retreating

0 5 10

Miles

GlacierBay

Pleasant Is.

Johns HopkinsGl.

Reid Gl.

GrandPacific Gl.

Canada

Alaska

1940 1912

1 899

1879

18791949

1879

1935

1760

17801830

1860

1913

1911

18921900

1879

1907 19481931

1941

1948

Case

men

t Gl.

McB

ride

Gl.

Plateau Gl.

Muir Gl.

Riggs Gl.

• Retreating glaciers

Figure 53.23


• 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.

Soil

nitro

gen

(g/m

2 )

Successional stagePioneer Dryas Alder Spruce

0

10

20

30

40

50

60

(a) Pioneer stage, with fireweed dominant

11


Equatorial-Polar Gradients

• The two key factors in equatorial-polar gradients of species richness

– Are probably evolutionary history and climate


• 2 main climatic factors correlated with biodiversity

– solar energy and water

(b) Vertebrates

500 1,000 1,500 2,000Potential evapotranspiration (mm/yr)

10

50

100

200

Ver

tebr

ate

spec

ies

richn

ess

(log

scal

e)

1100 300 500 700 900 1,100

180

160

140

120

100

80

60

40

20

0

Tree

spe

cies

rich

ness

(a) Trees Actual evapotranspiration (mm/yr)

Figure 53.25a, b


Area Effects

• 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


• species-area curve of North American breeding birds

Area (acres)

1 10 100 103 104 105 106 107 108 109 1010

Num

ber o

f spe

cies

(log

sca

le)

1

10

100

1,000

Figure 53.26


Island Equilibrium Model

• Species richness on islands

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


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

Immigration

Extin

ction

Extincti

on

Immigration

Extin

ctio

n

Immigration

(small island)

(larg

e isl

and)

(large island)

(sm

all is

land) Im

migration

Extin

ctio

n

Immigration

(far island)

(near island)

(near island) (far i

sland

)

Extincti

on

Rat

e of

imm

igra

tion

or e

xtin

ctio

n

Rat

e of

imm

igra

tion

or e

xtin

ctio

n

Rat

e of

imm

igra

tion

or e

xtin

ctio

n

12


• 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 o

f pla

nt s

peci

es (l

og s

cale

)

0.1 1 10 100 1,000

5

400

Figure 53.28


• 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

• The integrated hypothesis of community structure

– Describes a community as an assemblage of closely linked species, locked into association by mandatory biotic interactions


• The individualistic hypothesis of community structure

– Proposes that communities are loosely organized associations of independently distributed species with the same abioticrequirements


• 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 nearlyalways occur together.Figure 53.29a


• The individualistic hypothesis

– Predicts that each species is distributed according to its tolerance ranges for abioticfactors

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

13


• In most actual cases the composition of communities

– Seems to change continuously, with each species more or less independently distributed

Num

ber o

f pl

ants

per h

ecta

re

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

• 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


• The redundancy model of communities

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


• It is important to keep in mind that community hypotheses and models

– Represent extremes, and that most communities probably lie somewhere in the middle

Date post:	12-Apr-2018
Category:	Documents
Upload:	hadang
View:	215 times
Download:	2 times

53 community ecology - WordPress.com · Community Ecology Copyright © 2005 Pearson Education, Inc....

Documents