community structure & biodiversity. community all the populations that live together in a...
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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 coexistenceFigure 47.8
Page 825
PredationPredation
Predators are animals that feed Predators are animals that feed
on other living organismson other living organisms
Predators are free-living; they Predators are free-living; they
do not take up residence on do not take up residence on
their preytheir prey
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 hosts and live on or in
their bodiestheir bodies
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