Community Structure & Community Structure & BiodiversityBiodiversity

Community Community

All the populations that live together in a All the populations that live together in a

habitathabitat

Type of habitat shapes a community’s Type of habitat shapes a community’s structurestructure

Factors Shaping Factors Shaping Community StructureCommunity Structure

Climate and topographyClimate and topography Available foods and resourcesAvailable foods and resources Adaptations of species in communityAdaptations of species in community Species interactionsSpecies interactions Arrival and disappearance of species Arrival and disappearance of species Physical disturbancesPhysical disturbances

NicheNiche

Sum of activities and relationships in Sum of activities and relationships in

which a species engages to secure and which a species engages to secure and

use resources necessary for survival and use resources necessary for survival and

reproductionreproduction

Realized & Realized & Fundamental NichesFundamental Niches

Fundamental niche Fundamental niche Theoretical niche occupied in the absence of Theoretical niche occupied in the absence of

any competing speciesany competing species Realized niche Realized niche

Niche a species actually occupiesNiche a species actually occupies Realized niche is some fraction of the Realized niche is some fraction of the

fundamental nichefundamental niche

Species InteractionsSpecies Interactions

Most interactions are neutral; have no Most interactions are neutral; have no

effect on either specieseffect on either species

Commensalism helps one species and Commensalism helps one species and

has no effect on the otherhas no effect on the other

Mutualism helps both speciesMutualism helps both species

Species InteractionsSpecies Interactions

Interspecific competition has a negative Interspecific competition has a negative

effect on both specieseffect on both species

Predation and parasitism both benefit one Predation and parasitism both benefit one

species at a cost to anotherspecies at a cost to another

SymbiosisSymbiosis

Living together for at least some part of Living together for at least some part of

the life cyclethe life cycle

Commensalism, mutualism, and Commensalism, mutualism, and

parasitism are forms of symbiosisparasitism are forms of symbiosis

MutualismMutualism

Both species benefitBoth species benefit

Some are obligatory; partners Some are obligatory; partners

depend upon each otherdepend upon each other

Yucca plants and yucca mothYucca plants and yucca moth

Mycorrhizal fungi and plantsMycorrhizal fungi and plants

Yucca and Yucca MothYucca and Yucca Moth

Example of an obligatory mutualismExample of an obligatory mutualism

Each species of yucca is pollinated only by Each species of yucca is pollinated only by

one species of mothone species of moth

Moth larvae can grow only in that one Moth larvae can grow only in that one

species of yuccaspecies of yucca

Fig. 46-3a, p.823

Fig. 46-2b, p.822

Fig. 46-4, p.823

Sea Anemone and FishSea Anemone and Fish

CompetitionCompetition

Interspecific - between speciesInterspecific - between species

Intraspecific - between members of the Intraspecific - between members of the

same speciessame species

Intraspecific competition is most intenseIntraspecific competition is most intense

Forms of CompetitionForms of Competition

Competitors may have equal access to a Competitors may have equal access to a

resource; compete to exploit resource resource; compete to exploit resource

more effectivelymore effectively

One competitor may be able to control One competitor may be able to control

access to a resource, to exclude othersaccess to a resource, to exclude others

Interference CompetitionInterference Competition

Least chipmunk is Least chipmunk is

excluded from piñon excluded from piñon

pine habitat by the pine habitat by the

competitive behavior competitive behavior

of yellow pine of yellow pine

chipmunks chipmunks Yellow Pine Chipmunk

Least Chipmunk

Fig. 46-5a, p.824

Competitive Exclusion PrincipleCompetitive Exclusion Principle

When two species compete for identical When two species compete for identical

resources, one will be more successful resources, one will be more successful

and will eventually eliminate the otherand will eventually eliminate the other

Gause’s ExperimentGause’s Experiment

Paramecium caudatum

Paramecium aurelia Figure 47.6Page 825

Species grown together

Hairston’s ExperimentHairston’s Experiment

Two salamanders species overlap in parts Two salamanders species overlap in parts of their rangesof their ranges

Removed one species or the other in test Removed one species or the other in test plotsplots

Control plots unalteredControl plots unaltered 5 years later, salamander populations 5 years later, salamander populations

were growing in test plot were growing in test plot

Fig. 46-7, p.825

P. glutinosis

P. jordani

Resource PartitioningResource Partitioning

Apparent competitors may Apparent competitors may

have slightly different have slightly different nichesniches

May use resources in a May use resources in a different way or time different way or time

Minimizes competition and Minimizes competition and allows coexistenceallows coexistence

Figure 47.8  Page 825

PredationPredation

Predators are animals that feed on Predators are animals that feed on

other living organismsother living organisms

Predators are free-living; they do Predators are free-living; they do

not take up residence on their not take up residence on their

preyprey

CoevolutionCoevolution

Joint evolution of two or more species that Joint evolution of two or more species that exert selection pressure on each other as exert selection pressure on each other as an outcome of close ecological interactionan outcome of close ecological interaction

As snail shells have thickened, claws of As snail shells have thickened, claws of snail-eating crabs have become more snail-eating crabs have become more massivemassive

Predator-Prey ModelsPredator-Prey Models Type I model: Each individual predator will Type I model: Each individual predator will

consume a constant number of prey individuals consume a constant number of prey individuals over time over time

Type II model: Consumption of prey by each Type II model: Consumption of prey by each predator increases, but not as fast as increases predator increases, but not as fast as increases in prey densityin prey density

Type III model: Predator response is lowest Type III model: Predator response is lowest when prey density is lowestwhen prey density is lowest

Fig. 46-9a, p.826

Fig. 46-9c, p.826

Variation in CyclesVariation in Cycles

An association in predator and prey An association in predator and prey

abundance does not always indicate a abundance does not always indicate a

cause and effect relationshipcause and effect relationship

Variations in food supply and additional Variations in food supply and additional

predators may also influence changes in predators may also influence changes in

prey abundanceprey abundance

Canadian Lynx Canadian Lynx and Snowshoe Hareand Snowshoe Hare

Show cyclic oscillationsShow cyclic oscillations Krebs studied populations for ten yearsKrebs studied populations for ten years Fencing plots delayed cyclic declines Fencing plots delayed cyclic declines

but didn’t eliminate thembut didn’t eliminate them Aerial predators, plant abundance also Aerial predators, plant abundance also

involvedinvolved Three-level model Three-level model

Fig. 46-10a, p.827

Fig. 46-10b, p.827

Fig. 46-10c, p.827

Prey DefensesPrey Defenses

CamouflageCamouflage

Warning colorationWarning coloration

MimicryMimicry

Moment-of-truth Moment-of-truth

defensesdefenses

Fig. 46-11a, p.828

CamouflageCamouflage

Fig. 46-11b, p.828

CamouflageCamouflage

Fig. 46-11c, p.828

CamouflageCamouflage

Fig. 46-12a, p.829

MimicryMimicry

Fig. 46-12b, p.829

MimicryMimicry

Fig. 46-12c, p.829

MimicryMimicry

Fig. 46-12d, p.829

MimicryMimicry

Predator ResponsesPredator Responses

Any adaptation that protects prey may Any adaptation that protects prey may

select for predators that can overcome select for predators that can overcome

that adaptationthat adaptation

Prey adaptations include stealth, Prey adaptations include stealth,

camouflage, and ways to avoid chemical camouflage, and ways to avoid chemical

repellentsrepellents

Fig. 46-13a, p.829

Fig. 46-13b, p.829

Fig. 46-13d, p.829

ParasitismParasitism

Parasites drain nutrients from Parasites drain nutrients from

their hosts and live on or in their their hosts and live on or in their

bodiesbodies

Natural selection favors parasites Natural selection favors parasites

that do not kill their host too that do not kill their host too

quicklyquickly

Fig. 46-14a, p.830

Kinds of ParasitesKinds of Parasites

Microparasites Microparasites

Macroparasites Macroparasites

Social parasites Social parasites

ParasitoidsParasitoids

Fungus and FrogsFungus and Frogs

Amphibians are disappearing even in Amphibians are disappearing even in undisturbed tropical forests undisturbed tropical forests

Infection by a parasitic chytrid is one of the Infection by a parasitic chytrid is one of the causes of the recent mass deaths causes of the recent mass deaths

Parasitic PlantsParasitic Plants

HoloparasitesHoloparasites Nonphotosynthetic; withdraw nutrients and Nonphotosynthetic; withdraw nutrients and

water from young roots water from young roots

Hemiparasites Hemiparasites Capable of photosynthesis, but withdraw Capable of photosynthesis, but withdraw

nutrients and water from hostnutrients and water from host

Fig. 46-15a, p.830

Devil’s HairDevil’s Hair

Fig. 46-15b, p.830

Devil’s HairDevil’s Hair

ParasitioidsParasitioids

Insect larvae live inside and consume all Insect larvae live inside and consume all of the soft tissues of the host of the soft tissues of the host

Used as agents of biological controlUsed as agents of biological control

Can act as selective pressure on hostCan act as selective pressure on host

Fig. 46-17, p.831

The CowbirdThe Cowbird

Brown-headed cowbirds lay their eggs in Brown-headed cowbirds lay their eggs in nests constructed by other “host” bird nests constructed by other “host” bird species. These hosts are unable to species. These hosts are unable to differentiate between cowbird eggs and differentiate between cowbird eggs and their owntheir own

Cowbird hatchlings shove the other eggs Cowbird hatchlings shove the other eggs out of the owner’s nest and demand to be out of the owner’s nest and demand to be fed.fed.

The CowbirdThe Cowbird

Parasitic behavior has perpetuated Parasitic behavior has perpetuated cowbird genes for thousands of yearscowbird genes for thousands of years

Fig. 46-18a, p.831

Fig. 46-18b, p.831

Ecological SuccessionEcological Succession

Change in the composition of Change in the composition of species over timespecies over time

Classical model describes a Classical model describes a predictable sequence with a predictable sequence with a stable climax communitystable climax community

Types of SuccessionTypes of Succession

Primary succession - new Primary succession - new

environments environments

Secondary succession - Secondary succession -

communities were destroyed or communities were destroyed or

displaceddisplaced

Pioneer SpeciesPioneer Species

Species that colonize barren habitatsSpecies that colonize barren habitats

Lichens, small plants with brief life cyclesLichens, small plants with brief life cycles

Improve conditions for other species who Improve conditions for other species who

then replace themthen replace them

Climax CommunityClimax Community

Stable array of species that persists Stable array of species that persists

relatively unchanged over timerelatively unchanged over time Succession does not always move Succession does not always move

predictably toward a specific climax predictably toward a specific climax

community; other stable communities may community; other stable communities may

persistpersist

Fig. 46-19a, p.832

Fig. 46-19b, p.832

Cyclic ChangesCyclic Changes

Cyclic, nondirectional changes also shape Cyclic, nondirectional changes also shape

community structurecommunity structure Tree falls cause local patchiness in Tree falls cause local patchiness in

tropical foreststropical forests Fires periodically destroy underbrush in Fires periodically destroy underbrush in

sequoia forestssequoia forests

Fig. 46-20a, p.833

Fig. 46-20b, p.833

Fig. 46-20c, p.833

Restoration EcologyRestoration Ecology

Natural restoration of a damaged Natural restoration of a damaged

community can take a very long timecommunity can take a very long time Active restoration is an attempt to Active restoration is an attempt to

reestablish biodiversity in an area reestablish biodiversity in an area Ecologists are actively working to restore Ecologists are actively working to restore

reefs, grasslands, and wetlandsreefs, grasslands, and wetlands

Community InstabilityCommunity Instability

Disturbances can cause a Disturbances can cause a

community to change in ways community to change in ways

that persist even if the that persist even if the

change is reversedchange is reversed

Keystone SpeciesKeystone Species

A species that can dictate community A species that can dictate community

structurestructure

Removal of a keystone species can cause Removal of a keystone species can cause

drastic changes in a community; can drastic changes in a community; can

increase or decrease diversity increase or decrease diversity

Fig. 46-21a, p.834

Fig. 46-21b, p.834

Lubchenco ExperimentLubchenco Experiment

Tidepools Rocks exposed at high tide

Periwinkles promote or limit diversity in different habitats

Figure 47.21Page 834

Species IntroductionsSpecies Introductions

Introduction of a nonindigenous species Introduction of a nonindigenous species

can decimate a communitycan decimate a community

No natural enemies or controlsNo natural enemies or controls

Can outcompete native speciesCan outcompete native species