Population DynamicsPopulation Dynamics

Unit 10- Ecology Natural Unit 10- Ecology Natural DynamicsDynamics

Measuring PopulationsMeasuring Populations

• Population density = # of individuals Population density = # of individuals of a particular species per unit areaof a particular species per unit area

Measuring Populations, Measuring Populations, cont.cont.• Sampling – used to estimate size of Sampling – used to estimate size of

populationpopulation– Quadrats – count all organisms in a block Quadrats – count all organisms in a block

and use this to estimate population sizeand use this to estimate population size– Indirect counting – count nests, burrows, Indirect counting – count nests, burrows,

etc instead of organismsetc instead of organisms– Mark recapture – trap animals, mark Mark recapture – trap animals, mark

them, release, recapture and count them, release, recapture and count marked vs. unmarkedmarked vs. unmarked

Limiting population growthLimiting population growth

• Limiting factor – a condition that can Limiting factor – a condition that can limit population growthlimit population growth– Ex: space, food, diseaseEx: space, food, disease

• Carrying capacity – the number of Carrying capacity – the number of organisms in a population that the organisms in a population that the environment can maintain environment can maintain – Birth rate and death rate are about Birth rate and death rate are about

equalequal

Limiting population growthLimiting population growth

• Density-dependent factors – a factor Density-dependent factors – a factor that limits population growth more as that limits population growth more as the population density increasesthe population density increases– Ex: food, disease that spreads by Ex: food, disease that spreads by

contactcontact

• Density-independent factors – a Density-independent factors – a factor that limits population and is factor that limits population and is unrelated to population densityunrelated to population density– Ex: extreme weatherEx: extreme weather

Types of population growthTypes of population growth

• Exponential – population multiplies Exponential – population multiplies by a constant factor at constant time by a constant factor at constant time intervalsintervals– there are few factors that stop overall there are few factors that stop overall

growthgrowth– Also known as J-curveAlso known as J-curve

Types of population growthTypes of population growth

• S-curve – S-curve – population begins population begins growing growing exponentially, but exponentially, but environmental environmental factors begin to factors begin to limit growth; limit growth; population stops population stops growing or may growing or may begin to decreasebegin to decrease

Types of population growthTypes of population growth

• Boom and bust – increase rapidly Boom and bust – increase rapidly (boom) and then decrease rapidly (boom) and then decrease rapidly (bust)(bust)

Population interactionsPopulation interactions

• Interspecific competition – two or Interspecific competition – two or more species rely on the same limited more species rely on the same limited resourceresource– Competitive exclusion – when one Competitive exclusion – when one

species succeeds over the other due to species succeeds over the other due to limited resourceslimited resources

– Niche – each organism’s unique living Niche – each organism’s unique living arrangement, such as habitat, food, time arrangement, such as habitat, food, time when active, etcwhen active, etc

Population interactionsPopulation interactions

• Predation – an interaction in which Predation – an interaction in which one organism eats anotherone organism eats another– Predator – doing the eatingPredator – doing the eating– Prey – being eatenPrey – being eaten– Both predator and prey have evolved Both predator and prey have evolved

with adaptations to enhance survivalwith adaptations to enhance survival•Ex: camouflage, hunting in packs, warning Ex: camouflage, hunting in packs, warning

colorationcoloration

Prey adaptations

Population interactionsPopulation interactions

• Symbiotic relationships – a close Symbiotic relationships – a close relationship between species in which relationship between species in which one of the species lives in or on the otherone of the species lives in or on the other– Parasitism – the parasite obtains food at the Parasitism – the parasite obtains food at the

expense of the other organism (host)expense of the other organism (host)– Mutualism – both organisms benefitMutualism – both organisms benefit– Commensalism – one organisms benefits and Commensalism – one organisms benefits and

the other is neither helped nor harmedthe other is neither helped nor harmed

Parasitism – blowfly larvae kill purple martin chick

Mutualism – sea anemone protects clownfish from predators; clownfish is territorial and protects anemone from predators and shares food

Commensalism – grey whale carries barnacles; whale not harmed nor helped, barnacles have more access to food

bioaccumulation occurs within an organism, and biomagnification occurs across trophic (food chain) levels.

Disturbances in Disturbances in communitiescommunities

Ecological succession – community Ecological succession – community change when new species colonize change when new species colonize disturbed areadisturbed area– Primary succession – community arises in Primary succession – community arises in

lifeless area without soillifeless area without soil•Ex: volcano creating new islandEx: volcano creating new island

– Secondary succession – community arises Secondary succession – community arises in disturbed area with soilin disturbed area with soil•Ex: growth in plowed farm fieldEx: growth in plowed farm field

Primary succession – growth on lava rock

Secondary succession after forest fire

Disturbances in Disturbances in communitiescommunities

• Pioneer species – predominant Pioneer species – predominant species in the early stages of species in the early stages of succession; tend to be small, fast-succession; tend to be small, fast-growing, and fast-producinggrowing, and fast-producing

• Succession proceeds through many Succession proceeds through many stages until it reaches a stable end stages until it reaches a stable end point called the climax communitypoint called the climax community

Pioneer species – can grown on rock and will help form soil