AP Biology
Community Ecology
AP Biologybiosphere
ecosystem
community
population
Studying organisms in their environment
organism
AP Biology
Community Ecology! Community
" group of species living close enoughtogether for potential interaction
! Community Ecology" study of
interactionsamong allpopulationsin a commonenvironment
To answer:In what way do thepopulations interact?
AP BiologyFundamental
nichesRealizedniches
High tide
Low tide
Species 1
Species 2
Niche! An organism’s niche is its ecological role
habitat = address vs. niche = job
Competitive ExclusionCompetitive ExclusionIf Species 2 is removed,then Species 1 will occupywhole tidal zone. But atlower depths Species 2out-competes Species 1,excluding it from itspotential (fundamental)niche.
Chthamalus sp.
Semibalanus sp.
AP Biology
Niche & competition! Competitive Exclusion
" No two similar species can occupy thesame niche at the same time
AP Biology
Resource partitioningReduce competition through microhabitats
“the ghost ofcompetition past”
AP Biology
Interspecific interactions! Symbiotic interactions
" competition (-/-)! compete for limited resource
! 2 species cannot coexist in a communityif their niches are identical
" predation / parasitism (-/+)
" mutualism(+/+)! lichens (algae & fungus)
" commensalism (+/0)! barnacles attached
to whale
AP Biology
commensalism
mutualism
predation competition
Symbiosis
AP Biology
Predation drives evolution! Predators adaptations
" locate & subdue prey
! Prey adaptations" elude & defend
spines, thorns, toxins
horns, speed, coloration
Predation providesa strong selectionpressure on bothprey & predator
AP Biology
Defense mechanisms! Camouflage
" cryptic coloration
whippoorwill lizard
AP Biology frog
Cryptic coloration! Camouflage
toad
lizard
AP Biology
Warning “aposematic” coloration! Bright warning to predators
Monarch butterfly & larvae
AP Biology
Mimicrypalatable or harmless speciesmimics a harmful model
Hawkmoth Hawkmoth larva puffs up tolarva puffs up tolook like poisonous snakelook like poisonous snake
Batesian mimicry
hawkmoth larvae
green parrot snake
Convergent evolution
AP Biology
Batesian mimicry
Monarch malepoisonous
Viceroy maleedible
Which is the fly vs. the bee?Which is the moth vs. the bee?
Convergent evolution
fly bee moth bee
AP Biology
Mullerian mimicry
yellow jacket
cuckoo bee
two or more protectedspecies look like each other
- group defense?- group defense?
- predators may evolve innate avoidance- predators may evolve innate avoidance
AP Biology
What kind of mimicry?
Coral snake is poisonousKing snake is not
AP Biology
Coevolution! Predator-prey relationships! Parasite-host relationships! Flowers & pollinators
Long term evolutionary adjustments between species
AP Biology
Characterizing a community! Community structure
" species diversity! how many different species
" composition! dominant species! most abundant species
or highest biomass(total weight)
" keystone species! key role! strong effect on composition
of the community
AP Biology
Species diversitygreater diversity = greater stability
! Greater biodiversityoffers:" more food
resources" more habitats" more resilience
in face ofenvironmentalchange
AP Biology
suburban lawnagricultural“monoculture”
The impact of reduced biodiversity
“old field”
compare these communities
AP Biology
Keystone species! Influential ecological
role" exert important
regulating effect onother species incommunity
" keystonespeciesincreasesdiversityof habitat
Pisaster ochraceous
Sea star
diversity decreasesmussels out-competeother species
diversity increases
Washington coast
AP Biology
Keystone species
Sea otter is akeystonepredator inNorth Pacific
What is theWhat is theimpact of theimpact of theOrca whale?Orca whale?
AP Biology
Ecological succession! Sequence of community changes
" transition in species composition over time! years or decades
" usually after a disturbance
Mt. St. Helens
AP Biology
Primary succession! Begins with
virtuallylifeless areawithout soil,then…" bacteria" lichens &
mosses" grasses" shrubs" trees
makesoil{
AP Biology
Secondary succession! Existing community cleared,
but base soil is still intact
AP Biology
Succession of species
lichens & mosses grasses
treesbushes & small trees
pioneer species
climax forest
AP Biology
What causes succession?! Tolerance
" early species are weedy r-selected" tolerant of harsh conditions
! Facilitation & Inhibition" early species facilitate habitat changes
! change soil pH! change soil fertility! change light levels
" allows other speciesto out-compete
AP Biology
Climax forest! Plant community dominated by trees
! Representing final stage of naturalsuccession for specific location" stable plant community
" remains essentially unchanged in speciescomposition as long as site remains undisturbed
! birch, beech, maple,hemlock
! oak, hickory, pine
AP Biology
Climax forest
! solar energy levels! temperature! rainfall! fertility & depth of soil
The species mix ofclimax forest isdependent on theabiotic factors ofthe region
birch, beech, maple, hemlock
AP Biology
Disturbances as natural cycle! Disturbances are often necessary for
community development & survival-recycles nutrients
-increases biodiversity
-increases habitats
-rejuvenates community
fire climax forests
AP Biology
When people don’t learn ecology!
Building homes in fire climax zones
badidea!