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Chapter 27Chapter 27
Community Community InteractionsInteractions
Chapter 27 2
Exotic SpeciesExotic Species
Zebra mussels Zebra mussels (left)(left)
Brown tree snakes Brown tree snakes in Hawaiiin Hawaii
KudzuKudzu
Fire antsFire ants
Chapter 27 3
Why Are Exotic PopulationsWhy Are Exotic PopulationsOut of Control?Out of Control?
Native populations within communities have Native populations within communities have evolved togetherevolved together
Community persists in a delicate balance Community persists in a delicate balance between populationsbetween populations
Introduction of an "exotic" species destroys the Introduction of an "exotic" species destroys the balancebalance
Lack of coevolutionLack of coevolution• Two interacting species interacting over timeTwo interacting species interacting over time• Act as agents of natural selection on one anotherAct as agents of natural selection on one another
Chapter 27 4
Ecological NicheEcological Niche
Encompasses all aspects of a species’ way Encompasses all aspects of a species’ way of life, includingof life, including
• Physical home or Physical home or habitathabitat• Physical and chemical environmental Physical and chemical environmental
factors necessary for survivalfactors necessary for survival• How the species acquires its energy and How the species acquires its energy and
materialsmaterials• All the other species with which it interacts All the other species with which it interacts
Chapter 27 5
Community InteractionsCommunity InteractionsEcological nicheEcological niche
• No two species ever occupy exactly the same nicheNo two species ever occupy exactly the same niche• Niches of different species will overlapNiches of different species will overlap
Effects on balance of community of speciesEffects on balance of community of species• CompetitionCompetition• PredationPredation• SymbiosisSymbiosis
CompetitionCompetition• Interspecific competition helps control population sizeInterspecific competition helps control population size• Competitive exclusionCompetitive exclusion• Resource partitioning—develops during the course of Resource partitioning—develops during the course of
coevolutioncoevolution
Chapter 27 6
Reduction of Niche OverlapReduction of Niche Overlap
The The competitive exclusion principlecompetitive exclusion principle states that states that if two species occupy exactly the same if two species occupy exactly the same niche, one will eliminate the other niche, one will eliminate the other
Chapter 27 7
Competitive Exclusion:Competitive Exclusion:The Ciliate The Ciliate ParameciumParamecium over 24 d over 24 d
Grown inSeparateFlasks
Grown inthe SameFlask
Chapter 27 8
Reduction of Niche OverlapReduction of Niche Overlap
When species with largely overlapping When species with largely overlapping niches are allowed to compete, their niches are allowed to compete, their niches may focus on a different part of the niches may focus on a different part of the resource spectrumresource spectrum
• This is called This is called resource partitioningresource partitioning• This reduces interspecific competition This reduces interspecific competition • Example: North American warblersExample: North American warblers
Chapter 27 9
Resource PartitioningResource Partitioning
Chapter 27 10
Predator-Prey InteractionsPredator-Prey Interactions
Predators kill and eat other organismsPredators kill and eat other organisms• Broadly defined, Broadly defined, predatorspredators include include
herbivorous herbivorous as well as as well as carnivorous carnivorous organisms, including cows, pika, and bats organisms, including cows, pika, and bats hunting mothshunting moths
Predators tend to be larger and more Predators tend to be larger and more numerous than their preynumerous than their prey
Chapter 27 11
Evolutionary AdaptationsEvolutionary Adaptations
Predators have evolved characteristics that Predators have evolved characteristics that increase their chances of catching prey increase their chances of catching prey
• Examples: tearing claws of mountain lions Examples: tearing claws of mountain lions and keen eyesight of hawks and keen eyesight of hawks
Prey have evolved characteristics that Prey have evolved characteristics that decrease the chances of being eaten decrease the chances of being eaten
• Examples: dappling spots and motionless Examples: dappling spots and motionless behavior of deer fawnsbehavior of deer fawns
Chapter 27 12
Predator–Prey Interactions:Predator–Prey Interactions:Shape Evolutionary AdaptationsShape Evolutionary Adaptations
Camouflage—both predator and preyCamouflage—both predator and preyWarning colorationWarning colorationMimicry—prey species "evolve" resemblance to Mimicry—prey species "evolve" resemblance to
dangerous/poisonous speciesdangerous/poisonous speciesAggressive mimicry—predators resemble Aggressive mimicry—predators resemble
harmless species or objectsharmless species or objectsChemical warfareChemical warfare
• Bombardier beetleBombardier beetle• Plant chemicals, secondary metabolitesPlant chemicals, secondary metabolites• Venoms/poisonsVenoms/poisons
Chapter 27 13
CamouflageCamouflage
CamouflageCamouflage renders animals renders animals inconspicuous even when in plain inconspicuous even when in plain sightsight
• May include evolved colors, May include evolved colors, patterns, and shapes that patterns, and shapes that resemble one’s surroundingsresemble one’s surroundings
Chapter 27 14
Camouflage by Blending inCamouflage by Blending in
Sand dab (fish)Sand dab (fish)
Nightjar (bird)Nightjar (bird)
Chapter 27 15
CamouflageCamouflage
To avoid detection by predators, To avoid detection by predators, some animals have evolved to some animals have evolved to resemble objects such as bird resemble objects such as bird droppings, leaves, or thornsdroppings, leaves, or thorns
Chapter 27 16
Camouflage byCamouflage byResembling Specific ObjectsResembling Specific Objects
MothMoth
““poop”poop”Leafy Leafy Sea Sea DragonDragon
TreehoppersTreehoppers
Chapter 27 17
CamouflageCamouflage
Some plants have evolved to Some plants have evolved to resemble rocks to avoid detection resemble rocks to avoid detection by herbivoresby herbivores
Chapter 27 18
A Plant That Mimics a RockA Plant That Mimics a Rock
CactusCactus
Chapter 27 19
CamouflageCamouflage
CamouflageCamouflage also helps predators ambush also helps predators ambush their preytheir prey
• Examples: the cheetah blending with tall Examples: the cheetah blending with tall grass and the frogfish resembling a rockgrass and the frogfish resembling a rock
Chapter 27 20
Camouflage Assists PredatorsCamouflage Assists Predators(a)
(b)
CheetaCheeta
FrogfishFrogfish
Chapter 27 21
Bright ColorsBright Colors
Some animals have evolved bright Some animals have evolved bright warning warning colorationcoloration that attracts the attention of that attracts the attention of potential predators potential predators
• Advertises that they are distasteful or Advertises that they are distasteful or poisonous poisonous beforebefore the predator attacks the predator attacks
• Examples: poison arrow frogs, coral Examples: poison arrow frogs, coral snakes, and yellow jacketssnakes, and yellow jackets
Chapter 27 22
Warning ColorationWarning Coloration
Chapter 27 23
Protection Through MimicryProtection Through Mimicry
MimicryMimicry refers to a situation in which one refers to a situation in which one species has evolved to resemble another species has evolved to resemble another organism organism
Two or more distasteful species may each Two or more distasteful species may each benefit from a benefit from a sharedshared warning coloration warning coloration pattern (pattern (MMüüllerian mimicryllerian mimicry))
• Predators need only experience one distasteful Predators need only experience one distasteful species to learn to avoid all with that color species to learn to avoid all with that color patternpattern
Chapter 27 24
Chapter 27 25
Protection Through MimicryProtection Through Mimicry
Some harmless organisms can gain a Some harmless organisms can gain a selective advantage by resembling selective advantage by resembling poisonous species poisonous species (Batesian mimicry)(Batesian mimicry)
• Example: harmless hoverfly resembles beeExample: harmless hoverfly resembles bee• Example: harmless mountain king snake Example: harmless mountain king snake
resembles the venomous coral snakeresembles the venomous coral snake
Chapter 27 26
Chapter 27 27
Protection Through MimicryProtection Through Mimicry
Snowberry flies avoid by jumping spider Snowberry flies avoid by jumping spider predation by mimicking them both visually predation by mimicking them both visually and behaviorallyand behaviorally
Chapter 27 28
Visual and Behavioral MimicryVisual and Behavioral Mimicry(a)
(b)
Chapter 27 29
Protection Through MimicryProtection Through Mimicry
Some animals deter predators by employing Some animals deter predators by employing startle colorationstartle coloration
• Have spots that resemble eyes of a large Have spots that resemble eyes of a large predatorpredator
Chapter 27 30
Startle ColorationStartle Coloration
Swallowtail butterfly caterpillarSwallowtail butterfly caterpillar
Peacock mothPeacock moth
Chapter 27 31
Chemical WarfareChemical Warfare
Both predators and prey have evolved toxic Both predators and prey have evolved toxic chemicals for attack and defense chemicals for attack and defense
Spiders and poisonous snakes use venom Spiders and poisonous snakes use venom to paralyze their prey and deter predators to paralyze their prey and deter predators
Many plants have evolved chemicals to Many plants have evolved chemicals to deter herbivores deter herbivores
Bombardier beetle sprays hot chemicals Bombardier beetle sprays hot chemicals from its abdomenfrom its abdomen
Chapter 27 32
Chemical WarfareChemical Warfare
Chapter 27 33
Coevolutionary AdaptationsCoevolutionary Adaptations
Plants have evolved a variety of chemicals Plants have evolved a variety of chemicals to deter herbivoresto deter herbivores
• Example: the toxic and distasteful Example: the toxic and distasteful chemicals in milkweed chemicals in milkweed
Some animals evolve ways to detoxify these Some animals evolve ways to detoxify these chemicals, allowing them to eat the plantschemicals, allowing them to eat the plants
• Plants may then evolve other toxic Plants may then evolve other toxic substances substances
Chapter 27 34
The monarch The monarch butterfly uses butterfly uses deterrent deterrent chemicals of chemicals of milkweed, milkweed, acquired by a acquired by a feeding feeding caterpillar, to caterpillar, to make make itselfitself distasteful to its distasteful to its predatorspredators
Chapter 27 35
Symbiosis—a Close InteractionSymbiosis—a Close InteractionBetween Different SpeciesBetween Different Species
Parasitism—one benefits, other is harmedParasitism—one benefits, other is harmed
• Parasites smaller, more numerous than hostsParasites smaller, more numerous than hosts
• Parasites with higher reproductive rateParasites with higher reproductive rate
Commensalism—one benefits, other is neither Commensalism—one benefits, other is neither harmed nor benefitsharmed nor benefits
Mutualism—relationship benefits both speciesMutualism—relationship benefits both species
• RuminantsRuminants
• Nitrogen fixationNitrogen fixation
Chapter 27 36
SymbiosisSymbiosis
Chapter 27 37
Keystone SpeciesKeystone Species
In some communities a In some communities a keystone specieskeystone species plays a major role in determining plays a major role in determining community structurecommunity structure
Role is out of proportion to its abundanceRole is out of proportion to its abundanceRemoval of keystone species dramatically Removal of keystone species dramatically
alters community alters community
Chapter 27 38
Keystone SpeciesKeystone Species
Example: The predatory starfish Example: The predatory starfish PisasterPisaster from from Washington’s rocky intertidal coast Washington’s rocky intertidal coast
• When removed from their ecosystem their When removed from their ecosystem their favored prey, mussels, increase and favored prey, mussels, increase and competitively exclude other invertebrates and competitively exclude other invertebrates and algae, simplifying the communityalgae, simplifying the community
Example: Destruction of encroaching shrubs Example: Destruction of encroaching shrubs and trees by African elephantsand trees by African elephants
• Helps maintain the grass savanna which Helps maintain the grass savanna which supports many species supports many species
Chapter 27 39
Keystone Species: StarfishKeystone Species: Starfish
Chapter 27 40
Succession: PredictableSuccession: PredictableSequence of Community ChangesSequence of Community Changes
Primary succession—bare rock, barren Primary succession—bare rock, barren environmentsenvironments• No previously established ecosystemsNo previously established ecosystems• Occurs over a longer period of time (thousands of Occurs over a longer period of time (thousands of
years)years)• Pioneer speciesPioneer species• Climax community (influenced by environment)Climax community (influenced by environment)
Secondary succession—occurs in a disturbed, Secondary succession—occurs in a disturbed, established ecosystemestablished ecosystem• Plowed field, timbered forest, etc.Plowed field, timbered forest, etc.• Occurs over shorter time (hundreds of years)Occurs over shorter time (hundreds of years)
Chapter 27 41
Mount St. HelensMount St. Helensexplosion, 1980explosion, 1980
Same view,Same view,20 y later20 y later
Succession in ProgressSuccession in Progress
Chapter 27 42
SuccessionSuccession
During succession, most terrestrial During succession, most terrestrial communities go through stagescommunities go through stages
• Succession begins with arrival of a few hardy Succession begins with arrival of a few hardy invaders called invaders called pioneerspioneers
– They alter the ecosystem in ways that favor They alter the ecosystem in ways that favor other species, which eventually displace the other species, which eventually displace the pioneerspioneers
• Succession often progresses to a relatively Succession often progresses to a relatively stable and diverse stable and diverse climax communityclimax community
• Recurring disturbances can set back the Recurring disturbances can set back the progress of successionprogress of succession
– Maintain communities in Maintain communities in subclimax stagessubclimax stages
Chapter 27 43
Primary SuccessionPrimary Succession
Primary successionPrimary succession occurs “from scratch,” occurs “from scratch,” where there is no trace of a previous where there is no trace of a previous communitycommunity
• May take thousands or even tens of May take thousands or even tens of thousands of yearsthousands of years
• Examples: succession starting on bare Examples: succession starting on bare rock, sand, or in a clear glacial pool rock, sand, or in a clear glacial pool
Chapter 27 44
Primary SuccessionPrimary Succession
Chapter 27 45
Secondary SuccessionSecondary Succession
Secondary successionSecondary succession occurs after a occurs after a disturbance changes, but does not disturbance changes, but does not obliterate an existing communityobliterate an existing community
• Often takes just Often takes just hundreds of yearshundreds of years • Example: succession when a disturbance Example: succession when a disturbance
leaves behind soil and seedsleaves behind soil and seeds
Chapter 27 46
Secondary SuccessionSecondary Succession
Chapter 27 47
Succession in Ponds and LakesSuccession in Ponds and Lakes
Lakes and ponds form when a disturbance Lakes and ponds form when a disturbance blocks the flow of a river or streamblocks the flow of a river or stream
Nutrient influx, sediment deposition, and Nutrient influx, sediment deposition, and other aquatic processes can convert a other aquatic processes can convert a body of water into a bog, then to a dry body of water into a bog, then to a dry land communityland community
Chapter 27 48
Succession in a Freshwater PondSuccession in a Freshwater Pond
(a)(a)
(b)(b)
(c)(c)
Chapter 27 49
Climax CommunityClimax Community
Unless disturbances intervene, succession Unless disturbances intervene, succession usually ends with a relatively stable climax usually ends with a relatively stable climax communitycommunity
Species in climax communities have Species in climax communities have narrower niches than pioneer speciesnarrower niches than pioneer species
• Allows many species to coexist without Allows many species to coexist without replacing one anotherreplacing one another
Chapter 27 50
Climax CommunityClimax Community
Climax species tend to be larger and longer-Climax species tend to be larger and longer-lived than pioneer specieslived than pioneer species
The exact nature of the climax community at The exact nature of the climax community at a site reflects local geological and climatic a site reflects local geological and climatic conditionsconditions
• Examples: type of bedrock, temperature, Examples: type of bedrock, temperature, and rainfall and rainfall
Chapter 27 51
Subclimax StateSubclimax State
Frequent disturbances maintain subclimax Frequent disturbances maintain subclimax communities in some ecosystemscommunities in some ecosystems
Sub climax community example: Tallgrass prairies Sub climax community example: Tallgrass prairies that once covered northern Missouri and Illinoisthat once covered northern Missouri and Illinois
• Periodic fires prevented forest from encroachingPeriodic fires prevented forest from encroaching
Suburban lawnsSuburban lawns• Mowing and herbicides keep weeds and woody Mowing and herbicides keep weeds and woody
species in check species in check
AgricultureAgriculture• Plowing and pesticides keep competing weeds and Plowing and pesticides keep competing weeds and
shrubs from replacing early successional cereal shrubs from replacing early successional cereal grains grains
Chapter 27Chapter 27
The EndThe End