54 Lecture Presentation

8/2/2019 54 Lecture Presentation

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Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

PowerPointLecture Presentations for

BiologyEighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

Chapter 54

Community Ecology


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Overview: A Sense of Community

A biological communityis an assemblage of

populations of various species living close enough forpotential interaction. All life / all populations in anarea.

Ecologists call relationships between speciesin acommunity interspecific interactions.

Interspecific interactions can affect the survival andreproduction of each species. Effects can be positive

(+), negative (), or no effect (0). Examples: competition, predation, herbivory, and

symbiosis (parasitism, mutualism, commensalism).


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Competition

Interspecific competition(/ interaction)occurs when different species compete for aresource in short supply.

Strong competition can lead to competitive

exclusion, local elimination of a competingspecies.

The competitive exclusion principlestates

that two species competing for the samelimiting resources cannot coexist in the sameplace = 1 species per niche.


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Ecological Niches The total of a species use of biotic and abiotic

resourcesis called the speciesecological niche.

An ecological niche can also be thought of as anorganisms ecological role.

Ecologically similar species can coexist in acommunity if there are one or more significantdifferences in their niches.

Resource partitioningis differentiation of ecologicalniches; enables similar species to coexist in acommunity.


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Resourcepartitioningisdifferentiation

ofecologicalniches,enablingsimilarspeciesto coexist

in acommunity

A. ricordii

B. lizard speciesusually percheson shady branches.

A. Lizard speciesperches onfences and other sunny surfaces.

A. aliniger

A. distichus

A. insolitus

A. christophei

A. cybotes

A. etheridgei


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As a result of interspecific competition, aspecies fundamental niche may differ from itsrealized niche --> the niche it occupys afterresource partitioning.

Interspecific => Competition Between Species:Can Lead to Resource Partitioning


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How aspecies

niche can beinfluenced

byinterspecificcompetition?

Ocean

Chthamalus

Balanus

Later - Realized Niche

Ist - Fundamental Niche

High tide

Low tide

Chthamalus

realized niche

Balanus

realized niche

High tide

Chthamalus

fundamental niche

Low tideOcean


8/58Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Character Displacement

Character displacementis a tendency forcharacteristics / particular traits to be moredivergent in sympatric populations of twospecies than in allopatric populations of the

same two species.

An example is variation in beak size betweenpopulations of two species of Galpagos

finches.


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Characterdisplacement:

IndirectEvidenceof PastCompetition Los Hermanos

G. fuliginosa G. fortis

Beakdepth

Daphne

G. fuliginosa,allopatric

G. fortis,allopatric

Sympatricpopulations

Santa Mara, San Cristbal

Beak depth (mm)

Percentages

ofindividualsin

eachsizeclass

60

40

20

0

60

40

20

0

6040

20

08 10 12 14 16



Predation

Predation(+/ interaction) refers to interactionwhere one species, the predator, kills and eatsthe other, the prey.

Some feeding adaptations of predators areclaws, teeth, fangs, stingers, and poison.

Prey display various defensive adaptations:

such as behavior and coloration.



Behavioraldefenses include hiding, fleeing, formingherds or schools, self-defense, and alarm calls.

Animals also have morphologicalandphysiologicaldefense adaptations:

Cryptic coloration= camouflage, makes prey difficultto spot.

Aposematic coloration: Animals with effectivechemical defense /poison/ often exhibit brightwarning coloration. Predators are particularly cautiousin dealing with prey that display such coloration.

Prey: Defensive Adaptations


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Canyon tree frog

(a) Crypticcoloration

(b) AposematiccolorationPoison dart frog

(c) Batesian mimicry: A harmless species mimics a harmful one.Hawkmothlarva

Green parrot snakeYellow jacketCuckoo bee

Mllerian mimicry: Two yuckunpalatable species mimic each other.

(d)



In some cases, a prey species may gainsignificant protection by mimicking theappearance of another species:

In Batesian mimicry, a harmless speciesmimics an unpalatable or harmful model Oneis apretender.

In Mllerian mimicry, two or more unpalatablespecies resemble each other BOTHareyuck.

Mimicry = Look-alikes Defense



Herbivory: Herbivores = Plant Predators

Herbivory (+/ interaction) refers to aninteraction in which an herbivore eats parts of aplant or alga.

It has led to evolution of plant defensesagainst herbivores: secondary compounds=are chemical defenses; and mechanicaldefenses which are often osmoregulated.



Symbiosis: + + + 0 + -

Symbiosisis a dependency relationshipwheretwo or more species live in direct and intimatecontact with one another. The relationship isgenerally based one or some combination of

the following benefits:

Nutrition (food, water)

Protection

Reproduction



Parasitism + -

In parasitism (+/ interaction), one organism, theparasite, derives nourishment from another organism,its host, which is harmed in the process.

Endoparasites = parasites that live within the body of

their host. Ectoparasites = parasites that live on the external

surface of a host.

Many parasites have a complex life cycle involving anumber of hosts.

Some parasites change the behavior of the host toincrease their own fitness (reproduce more offspring).



Mutualism + +

Mutualistic symbiosis, or mutualism(+/+interaction), is an interspecific interaction thatbenefits both species.

A mutualism can be: Obligate = MUSTwhere one species cannot

survive without the other.

Facultative = OPTIONAL where both speciescan survive alone.


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Commensalism + 0

In commensalism (+/0 interaction), onespecies benefits and the other is apparentlyunaffected.

Commensal interactions are hard to documentin nature because any close association likelyaffects both species.

A ibl l f li b t ttl t (bi d ) d t


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A possible example of commensalism between cattle egrets (birds) and waterbuffalo: The Birds eat insects disturbed by the Buffalo as they move.

D i t d k t i t t


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Dominant and keystone species exert strongcontrols on community structure

A few species in a community often exertstrong control on that communitys structure.

Two fundamental features of community

structure = species diversity and feedingrelationships.


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Species Diversity

Species diversityof a community is the

variety of organisms that make up thecommunity.

It has two components: species richness and

relative abundance.

Species richness is the total number ofdifferent species in the community.

Relative abundance is the proportion eachspecies represents of the total individuals in thecommunity.


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Trophic Structure = a key factor in communitydynamics

Trophic structureis the feeding relationshipsbetween organisms in a community.

Food chains link trophic levels from producers to topcarnivores.

A food web is a branching food chain with complextrophic interactions.

Species may play a role at more than one trophiclevel.

Food chains in a food web are usually only a few linkslong. WHY?


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TerrestrialandMarine

FoodChains

Carnivore

Carnivore

Carnivore

Herbivore

Plant

A terrestrial food chain

Quaternaryconsumers

Tertiaryconsumers

Secondaryconsumers

Primaryconsumers

Primaryproducers

A marine food chain

Phytoplankton

Zooplankton

Carnivore

Carnivore

Carnivore

An Antarctic


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An AntarcticMarineFood Web

Humans

Smaller

toothedwhales

Baleenwhales Spermwhales

Elephantseals

Leopardseals

Crab-eaterseals

Birds Fishes Squids

Carnivorous

plankton

CopepodsEuphausids(krill)

Phyto-plankton

Li i F d Ch i L h


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Limits on Food Chain Length Food chains in food webs are usually only a few links

long.

Two hypotheses attempt to explain food chain length:the energetic hypothesisand the dynamic stability

hypothesis. The energetic hypothesissuggests that length is

limited by inefficient energy transfer.

The dynamic stability hypothesis proposes that longfood chains are less stable than short ones.

Most data support the energetic hypothesis.

S i i h L I


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Species with a Large Impact

Certain species have a very large impact oncommunity structure. Such species are highlyabundantOR play a pivotal rolein communitydynamics.

Dominant species= those that are mostabundant or have the highest biomass.

Biomassis the total mass of all individuals in apopulation. Dominant species exert powerfulcontrol over the occurrence and distribution ofother species.


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Invasive species, typically introduced to a newenvironment by humans, often lack predatorsor disease pathogens. Invasive species disruptecosystem dynamics. They frequently out-

compete / displace native populations.

K t S i


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Keystone Species Keystone speciesexert strong control on a

community by their ecological roles, or niches.

In contrast to dominant species, they are notnecessarily abundant in a community.

Field studies of sea stars exhibit their role as akeystone species in intertidal communities.

Sea otter populations and their predationshows how otters affect ocean communities.Sea otters are keystone predators in the North

Pacific.

Seastar are


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Seastar arekeystonepredators.They are key

in preservingspeciesdiversity intheir

ecosystem.

With Pisaster(control)

Without Pisaster(experimental)Numberofspecies

present

Year

20

15

10

5

01963 64 65 66 67 68 69 70 71 72 73

RESULTS

EXPERIMENT

Sea otters


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Sea ottersarekeystone

predatorsin theNorthPacific

(a) Sea otter abundance

O

tternumber

(%

max.count)

100

80

60

40

20

0

400

300

200

100

0(b) Sea urchin biomass

Grams

per

0.2

5m

2

10

8642

01972

Numberp

er

0.2

5m

2

1985 1997Year

(c) Total kelp densityFood chain

1989 1993

F d ti S i (E t E i )


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Foundation Species (Ecosystem Engineers)

Foundation species (ecosystem engineers)cause physical changes in the environmentthat affect community structure.

For example, beaver dams can transformlandscapes on a very large scale.

Some foundation speciesact asfacilitators

that have positive effects on survival andreproduction of some other speciesin thecommunity.

Beavers are a Foundation Species = ecosystemengineers


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Beavers are a Foundation Species = ecosystem engineers

B tt U d T D C t l


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Bottom-Up and Top-Down Controls

The bottom-up model of community

organization proposes a unidirectionalinfluence from lower to higher trophic levels.

In this case, presence or absence of mineral

nutrients determines community structure,including abundance of primary producers.

The top-down model, also called the trophic

cascade model,proposes that control comesfrom the trophic level above.

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

Disturbance influences species diversity and


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Disturbance influences species diversity andcomposition

Pollution can affect community dynamics.

Biomanipulation can help restore pollutedcommunities. Bio remediationis an effectivestrategy to restorepolluted and damaged

areas.

Decades ago, most ecologists favored the viewthat communities are in a state of equilibrium.

Recent evidence of change has led to anonequilibrium model, which describescommunities as constantly changing after

being buffeted by disturbances.


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The large-scale fire in Yellowstone National Park in 1988


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The large scale fire in Yellowstone National Park in 1988demonstrated that communities can often respond very rapidlyto a massive disturbance.

(a) Soon after fire (b) One year after fire

Ecological Succession


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Ecological Succession

Ecological successionis the

sequence ofcommunity and ecosystem changesafter adisturbance, over time.

Primary successionoccurs where no soilexists when succession begins. Pioneerorganisms, such as lichen, are the foundationof the community and soil building.

Secondary successionbegins in an areawhere soil remainsafter a disturbance /disastersuch as fire or field abandonment.


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Early-arriving species and later-arriving species

may be linked in one of three processes:

Early arrivals may facilitate appearance of laterspecies by making the environment favorable

They may inhibit establishment of later species

They may tolerate later species but have no

impact on their establishment Glacier retreating -- predictable pattern of

ecologial succession


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Pioneer stage = soil builders / fireweed dominant1


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Dryasstage grasses and shrubs2


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Alder stage: trees and shrub3


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Spruce stage = Climax Community STABLE4


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Changes in soil nitrogen content during succession at Glacier


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g g gBay

Successional stage

Pioneer Dryas Alder Spruce

Soilnitrogen(g/m2)

0

10

20

30

40

50

60

Human Disturbance


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Human Disturbance

Humans have the greatest impact on biologicalcommunities worldwide. Human disturbance tocommunities usually reduces species diversity.

Humans also prevent some naturally occurringdisturbances, which can be important tocommunity structure.

Disturbance of the ocean floor by trawling


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y g

Biogeographic factors affect community


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Biogeographic factors affect communitybiodiversity

Latitudeandareaare two key factors that

affect a communitys species diversity.

Species richness generally declines along anequatorial-polar gradient and is especially great

in the tropics. Two key factors in equatorial-polar gradientsof

species richness are probably evolutionary

historyandclimate. 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.

Two main climatic factors correlated withbiodiversity are solar energy and water

availability. They can be considered togetherby measuring a communitys rate of

evapotranspiration.

Evapotranspiration is evaporation of waterfrom soil plus transpiration of water from plants.

Area Effects


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Area Effects

The species-area curve quantifies the ideathat, all other factors being equal, a largergeographic area has more species.

A species-area curve of North Americanbreeding birds supports this idea.

Island Equilibrium Model


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Island Equilibrium Model

Species richness on islands depends onisland size, distance from the mainland,immigration, and extinction.

The equilibrium model of island biogeography

maintains that species richness on anecological island levels off at a dynamicequilibrium point.

Studies of species richness on the GalpagosIslands support the prediction that speciesrichness increases with island size.



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Number of species on island

Equilibrium number

(a) Immigration and extinction rates

Rateofimmig

rationorextinction

Rateofimmig

rationorextinction


(b) Effect of island size

Small island Large island

(c) Effect of distancefrom mainland


Rateofimmig

rationorextinction

Far island Near island

Community ecology is useful for understanding


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Community ecology is useful for understandingpathogen life cycles and controlling human disease

Ecological communities are universally affectedby pathogens, which include disease-causingmicroorganisms, viruses, viroids, and prions.

Pathogens can alter community structurequickly and extensively.

For example, coral reef communities are beingdecimated by white-band disease.

White-band disease on coral is destroying the reef.


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Community Ecology and Zoonotic Diseases


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Co u ty co ogy a d oo ot c seases

Human activities are transporting pathogens around

the world at unprecedented rates. Community ecology is needed to help study and

combat them.

Zoonotic pathogens have been transferred from otheranimals to humans.

The transfer of pathogenscan be direct or through anintermediate species called a vector.

Many of todays emerging human diseases arezoonotic. Avian flu is a highly contagious virus of birds.

Review


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You should now be able to:


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1. Distinguish between the following sets ofterms: competition, predation, herbivory,symbiosis; fundamental and realized niche;cryptic and aposematic coloration; Batesian

mimicry and Mllerian mimicry; parasitism,mutualism, and commensalism;endoparasites and ectoparasites; speciesrichness and relative abundance; food chainand food web; primary and secondarysuccession.


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2. Define an ecological niche and explain thecompetitive exclusion principle in terms of theniche concept.

3. Explain how dominant and keystone speciesexert strong control on community structure.

4. Distinguish between bottom-up and top-down

community organization.

5. Describe and explain the intermediatedisturbance hypothesis.


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6. Explain why species richness declines alongan equatorial-polar gradient.

7. Define zoonotic pathogens and explain, with

an example, how they may be controlled.

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54 Lecture Presentation