PopulationsPopulationsGroup of individuals that belong to the Group of individuals that belong to the same species and live in the same areasame species and live in the same area

Chapter 5

California Biology Science Standards

B1 6.b. Students know how to analyze changes in an ecosystem from changes in climate, human activity, introduction of nonnative species, or changes in populations size.

B1 6.c. Students know how fluctuations in population size in an ecosystem are determined by the relative rates of birth, immigration, emigration, and death.

Characteristics of Characteristics of PopulationsPopulations

1. Geographic distribution1. Geographic distribution::

- area inhabited by a population- area inhabited by a population

- can range in size and shape- can range in size and shape

2. 2. Population Density:Population Density:

- the # of individuals per unit area- the # of individuals per unit area

- # can vary - # can vary

3. 3. Population Growth:Population Growth:

- how a population grows or - how a population grows or decreases decreases

in sizein size

Factors that affect population Factors that affect population sizesize

1.1. # of births# of births

2.2. # of deaths# of deaths

3.3. # of individuals that enter or leave # of individuals that enter or leave a populationa population

Scenarios:Scenarios:- If population grows?If population grows?- If population decrease?If population decrease?- If population stays the same?If population stays the same?

ImmigrationImmigration

Movement of individuals into a Movement of individuals into a populationpopulation

Cause population to increase in sizeCause population to increase in size

EmmigrationEmmigration

Movement of individuals out of a Movement of individuals out of a populationpopulation

Causes population to decrease in sizeCauses population to decrease in size

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

Section 5-1

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Population Growth Concept Map

Exponential GrowthExponential Growth- Occurs when the individuals in a population - Occurs when the individuals in a population

reproduce at a constant ratereproduce at a constant rate- in the beginning #’s increase slowly- in the beginning #’s increase slowly- over time the pop. becomes so large it is - over time the pop. becomes so large it is

exponential exponential (VERY BIG !!!!!!!!)(VERY BIG !!!!!!!!)- Only can happen when the pop. has:Only can happen when the pop. has:

1. abundant space & food1. abundant space & food2. protection from predators & disease2. protection from predators & disease3. the ability to reproduce3. the ability to reproduce

*** does not continue for a long time****** does not continue for a long time***

Examples of Exponential Examples of Exponential GrowthGrowth

Find graphs on internetFind graphs on internet

Logistic GrowthLogistic Growth- Occurs when a populations growth Occurs when a populations growth

slows or stops following a period of slows or stops following a period of exponential growthexponential growth

- Caused by:Caused by:

1. resources become less available1. resources become less available

2. birthrate 2. birthrate ↓ deaths ↑ ↓ deaths ↑ oror they are equal they are equal

3. immigration ↓ emmigration ↑ 3. immigration ↓ emmigration ↑ or or

they are equalthey are equal

Carrying Capacity

• The largest # of individual that a given environment can support

Nu m

ber

of Y

east

Cel

l s

Time (hours)

Carrying capacity

Section 5-1

Figure 5-4 Logistic Growth of Yeast Population

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Limits to GrowthLimits to Growth

Limiting Factor:Limiting Factor:

- a factor that causes population - a factor that causes population growth to decreasegrowth to decrease

- can be Density Dependent - can be Density Dependent oror

Density IndependentDensity Independent

Density – Dependent Density – Dependent FactorsFactors

Limiting factors that depend on Limiting factors that depend on population sizepopulation size

Become limiting only when the Become limiting only when the population density (# of individuals) population density (# of individuals) reach a certain levelreach a certain level

Affect very large populations only Affect very large populations only

Types of Density Dependent Types of Density Dependent FactorsFactors

1. 1. Competition Competition – when populations – when populations become crowded, they start to compete become crowded, they start to compete for: food, water, space & sunlightfor: food, water, space & sunlight

- can be among the same species or - can be among the same species or different speciesdifferent species

2. 2. PredationPredation – often controls populations – often controls populations in nature ** predator/prey in nature ** predator/prey relationships**relationships**

3. 3. Parasitism & DiseaseParasitism & Disease – take – take nourishment from the host causing nourishment from the host causing death or disease.death or disease.

Density-Independent Density-Independent FactorsFactors

Affect all populations regardless of Affect all populations regardless of sizesize

Types:Types:

1. unusual weather 1. unusual weather

2. natural disasters2. natural disasters

3. seasonal cycles3. seasonal cycles

4. human activities4. human activities

How populations respond to the How populations respond to the factorsfactors

Populations size crashesPopulations size crashes But most will build up again or may stay But most will build up again or may stay

low for some timelow for some time

Always Remember….Always Remember….

1.1. Environments are always changingEnvironments are always changing

2.2. Most populations can adapt to the changesMost populations can adapt to the changes

3.3. Population will grow & shrink in responsePopulation will grow & shrink in response

4.4. Major upsets can lead to long term decline Major upsets can lead to long term decline (usually caused by human activity)(usually caused by human activity)

Human Population Human Population GrowthGrowth

Like other organisms, human population tends to Like other organisms, human population tends to increase with timeincrease with time

For most of human existence – population has For most of human existence – population has grown slowly (limited food source/incurable grown slowly (limited food source/incurable disease)disease)

About 500 years ago – population began growing About 500 years ago – population began growing more rapidlymore rapidly

Causes: agriculture & industry (easier & safer)Causes: agriculture & industry (easier & safer)

food supply more reliablefood supply more reliable

goods shipped around the worldgoods shipped around the world

improved sanitationimproved sanitation Result: decreased death rate & birthrate increaseResult: decreased death rate & birthrate increase So….. Humans experienced EXPONENTIAL So….. Humans experienced EXPONENTIAL

GROWTHGROWTH

Agriculturebegins

Plowingand irrigation

Bubonicplague

IndustrialRevolutionbegins

Section 5-3

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Human Population Growth