Unit 17—Ecology (& Populations)Ch. 30 Populations & Communities

(sec. 1 & 4)

Populations, Communities, & Ecosystems (Sec. 1)

• What is a population?– All organisms of same type in the area

• What is a community?– All different organisms (populations) in the area

• What is an ecosystem?– All organisms & non-living (abiotic) factors in the area

Population Size & Arrangement• How can populations be counted?

– Animals• Ear tags• Leg bands• Radio transmitters

– Plants• Marked w/ paint or ribbons

• What if a population is too large to count every individual?– Estimate using sampling techniques

• Count # in a small area, then multiply by total area

• mark & recapture Mark & Recapture Animation

Mark & Recapture Game

Population Size & Arrangement• How can a population distributed/

arranged in an area?– random– uniform– clumped

• What might be an advantage of a clumped population?

• What is population density?– # individuals/area

• Ex. 1000 people/mile2

What type of population distribution can be seen in the US? CT?

• What can cause an increase in the population size of an area?– births– immigration

• What can cause a decrease in the population size of an area? – deaths– emigration

• Can you come up with an equation to show overall population change?– Population change = (B + I – D – E) or (B + I) – (D + E)

• Is population decreasing or increasing if change is:– positive?– negative?

Population Changes

• population pyramids (a.k.a. age structure diagrams)– basic shape can help us predict what’s going to happen to

the population in the future…– What do you think will happen to the population in each pyramid???

Rapid GrowthGuatemala

NigeriaSaudi Arabia

Negative GrowthGermanyBulgariaSweden

Zero GrowthSpain

AustriaGreece

Slow GrowthU. S.

AustraliaCanada

Ages 0-14 Ages 45+Ages 15-44

Visualizing Population Structures & Predicting Future Changes

How Population Pyramids Are Made Video

Animated Population Pyramid

Developing Countries– Wide base– High #s of pre- &

reproductive age• High birth rates

– fast growth

Developed Countries– slightly wider base, width is

same, or inverted pyramid– lower #s of pre- &

reproductive age– low birth rates

• slow growth, zero growth, negative growth (pop. shrinks)

Population Pyramids(Age Structure Diagrams)

Population growth rate by country

Population Clock

Population Growth• Types of population

growth:– exponential growth

• represents species’ biotic potential

– ideal conditions

– Logistic growth• population reaches

“carrying capacity”

point of maximum growth

Logistic Growth

Exponential Growth

Population Growth• Why don’t populations

increase forever?– limiting factors

• provide environmental resistance

• prevent population from growing indefinitely

– reach “carrying capacity”

• can be:– abiotic (non-living)– biotic (living)

Examples of Abiotic Limiting Factors

• Organisms have a “range of tolerance” for abiotic factors– Thrive under some conditions (optimal range)– Survive, but are not well (stress zone)– Can’t survive (zone of intolerance)

Abiotic Limiting Factors

• Is temperature a limiting factor for these fish species?– Why/why not?

Abiotic Limiting Factors

optimal temperature

Examples of Biotic Limiting Factors• Living factors in an ecosystem

Decomposers are heterotrophsBreak down dead material & recycle nutrients

Biotic Limiting Factors

• Usually described in terms of interactions– especially

who eats whom or trophic levels

Other Relationships in a Community

• symbiosis– when 2

species live closely together in a relationship over time

Other Relationships in a Community: Commensalism

• One partner benefits from the relationship & the other neither benefits, nor is harmed

Other Relationships in a Community: Mutualism

• Both partners benefit from the relationship.

Other Relationships in a Community: Parasitism

• One partner benefits (parasite), & the other is harmed (host)

Other Relationships in a Community: Predation

• One organism benefits (predator), the other is harmed (prey)