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!