Chapter 4: PopulationsChapter 4: Populations

EQ: How would changes in populations affect the EQ: How would changes in populations affect the flow of energy and matter in the ecosystem? flow of energy and matter in the ecosystem? EQ: How are populations regulated over time? EQ: How are populations regulated over time? EQ: How does the growing human population threaten EQ: How does the growing human population threaten the biosphere?the biosphere?

Georgia Performance Standards:

•Investigate the relationships among organisms, populations, communities, ecosystems, and biomes.

Warm-up:Warm-up:

A laboratory jar containing a population A laboratory jar containing a population of beetle larvae (mealworms) has of beetle larvae (mealworms) has reached a stable population size. We reached a stable population size. We decide to add twice as much food per decide to add twice as much food per day to the jar, but this turns out to have day to the jar, but this turns out to have no effect on population size. no effect on population size.

What is the most likely explanation?What is the most likely explanation?

Populations Populations

Defined by different Defined by different geographical geographical boundariesboundaries

Important Important characteristics:characteristics: DensityDensity Geographical Geographical

DistributionDistribution Growth RateGrowth Rate Age StructureAge Structure

What is What is POPULATION DENSITYPOPULATION DENSITY??

The number of individuals The number of individuals of a species per unit area of a species per unit area or volumeor volume..

Three factors can affect Three factors can affect population sizepopulation size # of births# of births

# of deaths# of deaths

# of individuals that enter # of individuals that enter or leave the population or leave the population

ImmigrationImmigration (im-uh-(im-uh-gray-shun), the gray-shun), the movement of individuals movement of individuals into an area, can cause into an area, can cause a population to a population to growgrow. .

EmigrationEmigration (em-uh- (em-uh-gray-shun), the gray-shun), the movement of individuals movement of individuals out of a population, can out of a population, can cause a population to cause a population to decreasedecrease in size. in size.

How do populations grow?How do populations grow?

Exponential GrowthExponential Growth Under ideal conditions Under ideal conditions

with unlimited resources, with unlimited resources, a population will grow a population will grow exponentiallyexponentially

The whole population The whole population multiplies by a constant multiplies by a constant factor during constant factor during constant time intervalstime intervals

Organisms do not Organisms do not usually grow usually grow exponentially for very exponentially for very long.long.

ExponentialExponential Growth Growth

Both of these Both of these hypothetical graphs hypothetical graphs show the characteristic show the characteristic J-shape of exponential J-shape of exponential population growthpopulation growth. .

Logistic GrowthLogistic Growth

  As resources As resources become less become less available, the available, the growth of a growth of a population slows or population slows or stops= stops= Logistic Logistic growthgrowth

Can follow a period of Can follow a period of exponential growthexponential growth

•S-shaped curve of this growth pattern

•birthrate=deathrate immigration =emigration

Logistic Growth of Yeast Population

Time (hours)

Num

ber of yeast cells

Carrying Capacity

Carrying CapacityCarrying Capacity

The number of individuals in a population The number of individuals in a population that the environment can just maintain that the environment can just maintain with no net increase or decreasewith no net increase or decrease

PopulationGrowth

can be

represented bycharacterized by characterized by represented by

which cause a

Exponentialgrowth

Logisticgrowth

Fallinggrowth rate

S-shapedcurve

Limits ongrowth

No limits on growth

J-shapedcurve

Constantgrowth rate

Unlimitedresources

Concept Map

5–1 Summary:5–1 Summary:How Populations Grow How Populations Grow

Three important characteristics of a Three important characteristics of a population are: population are: geographic distributiongeographic distribution density density growth rate.growth rate.

Three factors affect population size: Three factors affect population size: # of births# of births

# deaths, # deaths, # of individuals that enter or # of individuals that enter or leave the populationleave the population..

Under ideal conditions and unlimited Under ideal conditions and unlimited resources, a population will continue resources, a population will continue to grow in a pattern called to grow in a pattern called exponential growth. As resources exponential growth. As resources are used up and population growth are used up and population growth slows or stops, the population slows or stops, the population exhibits logistic growth.exhibits logistic growth.

VocabularyVocabulary

population density population density

immigration immigration

emigration emigration

exponential growth exponential growth

logistic growth logistic growth

carrying capacitycarrying capacity

Checkpoint!!!Checkpoint!!!

Which of the following is NOT a Which of the following is NOT a condition for a population to reach condition for a population to reach exponential growth?exponential growth? presence of unlimited resources presence of unlimited resources absence of predation and disease absence of predation and disease movement of individuals out of a populationmovement of individuals out of a population

EQ: EQ:

How are populations How are populations regulated over time?regulated over time?

Population Limiting FactorsPopulation Limiting Factors

Environmental factors that restrict population Environmental factors that restrict population growth.growth.

Some limiting factors depend on the size of the Some limiting factors depend on the size of the population. population.

Other limiting factors affect all populations in Other limiting factors affect all populations in similar ways, regardless of the population size.similar ways, regardless of the population size.

Warm-up: Population Limiting Warm-up: Population Limiting FactorsFactors

1. Imagine a small island that has a population of five 1. Imagine a small island that has a population of five rabbits. How might each of the following factors affect rabbits. How might each of the following factors affect the rabbit population?the rabbit population?

a. climatea. climateb. food supplyb. food supplyc. predationc. predation

2. Now imagine another small island that has a population 2. Now imagine another small island that has a population of 500 rabbits. How would the same factors affect this of 500 rabbits. How would the same factors affect this population?population?

3. Which of the factors depend on population size? Which 3. Which of the factors depend on population size? Which factors do not depend on population size?factors do not depend on population size?

Density-dependent FactorsDensity-dependent Factors

Factors that depend on Factors that depend on the population densitythe population density

Factors affect a greater Factors affect a greater percentage of individuals percentage of individuals in a population as the in a population as the number of individuals number of individuals increases.increases.

Death rate increases and Death rate increases and the birth rate decreasesthe birth rate decreases

Limited food supplyLimited food supply CompetitionCompetition PredationPredation ParasitismParasitism DiseaseDisease

Buildup of poisonous Buildup of poisonous wasteswastes

Density-independent Density-independent FactorsFactors

Limiting factors whose Limiting factors whose occurrence is not affected occurrence is not affected by population densityby population density

Abiotic factors; climate and Abiotic factors; climate and weather or natural disasters weather or natural disasters and human activityand human activity

Affect the same percentage of Affect the same percentage of individuals regardless of the individuals regardless of the population size.population size.

Abiotic factorsAbiotic factors

climate and weatherclimate and weather natural disastersnatural disasters human activityhuman activity

Damming riversDamming rivers Clear-cutting forestsClear-cutting forests

5–2 Summary: Limits to Growth5–2 Summary: Limits to Growth    

Density-dependent Density-dependent limiting factors include limiting factors include competition, predation, competition, predation, parasitism, and disease.parasitism, and disease.

Unusual weather, natural Unusual weather, natural disasters, seasonal disasters, seasonal cycles, and certain cycles, and certain human activities—such human activities—such as damming rivers and as damming rivers and clear-cutting forests—clear-cutting forests—are all examples of are all examples of density-independent density-independent limiting factorslimiting factors..

VocabularyVocabulary limiting factor limiting factor

density-dependent density-dependent limiting factor limiting factor

predator-prey predator-prey relationship relationship

density-independent density-independent limiting factor limiting factor

The Human PopulationThe Human Population

EQ: How does the growing human EQ: How does the growing human population threaten the biosphere?population threaten the biosphere?

The size of the human population The size of the human population

tends to increase with timetends to increase with time

DemographyDemography

The scientific study of The scientific study of human populationshuman populations

Birth ratesBirth rates

Death ratesDeath rates

Age structure of Age structure of populationpopulation

All help to predict All help to predict why some why some countries have high countries have high growth rates while growth rates while other countries other countries grow more slowly.grow more slowly.

Demographic TransitionDemographic Transition

A dramatic change in A dramatic change in birth and death ratesbirth and death rates

The demographic The demographic transition is complete transition is complete when the birthrate falls when the birthrate falls to meet the death rate, to meet the death rate, and population growth and population growth stops.stops.

Birthrates and death rates fall during the demographic Birthrates and death rates fall during the demographic transition. Initially, both rates are high (A). Then, the death transition. Initially, both rates are high (A). Then, the death rate drops while the birthrate remains high (B). Finally, the rate drops while the birthrate remains high (B). Finally, the birth rate also decreases (C). birth rate also decreases (C).

Age-structure diagramsAge-structure diagrams

A population profile that can predict A population profile that can predict future growth.future growth.

Shows the number of people in different Shows the number of people in different age groups in the populationage groups in the population

HumanActivities

that have changed the biosphere include

may have once caused often relies on the methods of thehave resulted in

which increased

Food supply Pesticide use Monocultureuse

Hunting andgathering Agriculture

Industrial growth

Urbandevelopment

Extinctions oflarge animals

Greenrevolution

High standardof living

Increasedpollution

Section 6-1

Go to Section:

Threats to BiodiversityThreats to Biodiversity

Human activity can Human activity can reduce biodiversity by reduce biodiversity by altering habitats (altering habitats (Habitat Habitat fragmentationfragmentation), hunting ), hunting species to extinction, species to extinction, introducing toxic introducing toxic compounds into food compounds into food webs, and introducing webs, and introducing foreign species (foreign species (Invasive Invasive speciesspecies) to new ) to new environments. environments.

ExtinctionExtinction occurs when a occurs when a species disappears from all or species disappears from all or part of its range. part of its range.

A species whose population A species whose population size is declining in a way that size is declining in a way that places it in danger of places it in danger of extinction is called an extinction is called an endangered speciesendangered species. .

As the population of an As the population of an endangered species declines, endangered species declines, the species loses genetic the species loses genetic diversity diversity

5–3 Summary: Human Population 5–3 Summary: Human Population GrowthGrowth

Like the populations of Like the populations of many other living many other living organisms, the size of the organisms, the size of the human population tends to human population tends to increase with time.increase with time.

The characteristics of The characteristics of populations, and the social populations, and the social and economic factors that and economic factors that affect them, explain why affect them, explain why some countries have high some countries have high population growth rates population growth rates while populations of other while populations of other countries grow slowly or countries grow slowly or not at all.not at all.

VocabularyVocabulary demography demography

demographic demographic transition transition

age-structure diagram age-structure diagram