How populations grow

How populations grow 3 important characteristics of a

population are -


population are – Geographic distribution -


population are – Geographic distribution – describes the

area inhabited by a population


population are – Population density -


population are – Population density – number of

individuals per unit area



individuals per unit area• Example of low density -



individuals per unit area• Example of low density –• Example of high density -


population are – Growth rate -


population are – Growth rate – the speed at which a

population may change in numbers

How populations grow Three factors that can affect

population size


population size The number of births


population size The number of births The number of deaths


population size The number of births The number of deaths The number of individuals that enter or

leave a population

How populations grow Immigration -

How populations grow Immigration – the movement of

individuals into an area


individuals into an area Example -


individuals into an area Example – animals in search of mates

or food arrive from outside the population

How populations grow Emigration -

How populations grow Emigration – the movement of

individuals out of a population


individuals out of a population Example -


individuals out of a population Example – young animals approach

maturity and leave area to establish new territories

How populations grow Exponential growth -

How populations grow Exponential growth – occurs when

the individuals in a population reproduce at a constant rate

Exponential growth A graph of exponential growth would

be


be J-shaped


be J-shaped Example -


be J-shaped Example - bacteria


be J-shaped Example – bacteria

• Usually occurs



• Usually occurs under ideal conditions with



• Usually occurs under ideal conditions with unlimited resources

Exponential growth Bacteria - some are able to

reproduce every 20 minutes


reproduce every 20 minutes If you begin with one bacteria



• 20 minutes later there will be 2



• 20 minutes later there will be 2• Another 20 minutes there will be __



• 20 minutes later there will be 2• Another 20 minutes there will be 4



• 20 minutes later there will be 2• Another 20 minutes there will be 4• Another 20 minutes there will be ___



• 20 minutes later there will be 2• Another 20 minutes there will be 4• Another 20 minutes there will be 8• In another hour there will be ___



• 20 minutes later there will be 2• Another 20 minutes there will be 4• Another 20 minutes there will be 8• In another hour there will be 64• In 2 more hours there will be ___



• 20 minutes later there will be 2• Another 20 minutes there will be 4• Another 20 minutes there will be 8• In another hour there will be 64• In 2 more hours there will be 512• In just one day there will be ___

Exponential growth Bacteria - some are able to reproduce

every 20 minutes If you begin with one bacteria

• 20 minutes later there will be 2• Another 20 minutes there will be 4• Another 20 minutes there will be 8• In another hour there will be 64• In 2 more hours there will be 512• In just one day there will be

4,720,000,000,000,000,000,000

How population grow Logistic growth -

How population grow Logistic growth – occurs when a

population’s growth slows or stops following a period of exponential growth


population’s growth slows or stops following a period of exponential growth Why might this happen?





• Birthrate decreases



• Birthrate decreases• Deathrate increases



• Birthrate decreases• Deathrate increases• Or both events occur at same time



• Birthrate decreases• Deathrate increases• Or both events occur at same time

Logistic growth

Time (hours)

Num

ber o

f yeast ce

lls

Logistic growth Graph would be

“S-shaped”

Time (hours)

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lls


“S-shaped” Initial growth

would be ___

Time (hours)

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would be slow, followed by a period of ___

Time (hours)

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would be slow, followed by a period of rapid growth

Time (hours)

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Growth then___Time (hours)

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Growth then levels off

Time (hours)

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Logistic growth Caused by some

sort of __________________ on the

population.

Time (hours)

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Logistic growth Caused by some

sort of limitingfactor on the

population.

Time (hours)

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Logistic growth Carrying capacity -

Time (hours)

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the largest number of individuals that a given environment can support

Time (hours)

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What if conditions

change?

Time (hours)

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What if conditions

change? The carrying

capacity will also change

Time (hours)

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ber o

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lls


Where is carrying

capacity on “S” shaped curve?

Time (hours)

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ber o

f yeast ce

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Where is carrying

capacity on “S” shaped curve?

Time (hours)

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ber o

f yeast ce

lls

Carrying capacity

Limits on growth Limiting factors -

Limits on growth Limiting factors – a factor that

causes population growth to decrease


causes population growth to decrease Examples -


causes population growth to decrease Examples –

• competition



• Competition• predation



• Competition• Predation• Parasitism and disease



• Competition• Predation• Parasitism and disease• Drought and other climate extremes



• Competition• Predation• Parasitism and disease• Drought and other climate extremes• Human disturbances

Limits on growth Density-dependent factors -

Limits on growth Density-dependent factors – a

limiting factor that depends on population size;

Limits on growth Density-dependent factors – a

limiting factor that depends on population size; limits only when population density reaches a certain level

Limits on growth Density-dependent factors –

Growth rate _________ as density _________


Growth rate decreases as density increases



Growth pattern -



Growth pattern – “S” shaped curve

Density-dependent factors Competition


When populations become crowded, organisms compete, or struggle, with one another for food, water, space, sunlight, and other essentials of life


When populations become crowded, organisms compete, or struggle, with one another for food, water, space, sunlight, and other essentials of life

The more individuals that live in an area, the sooner they will use up the available resources

Density-dependent factors Predation -

Density-dependent factors Predation – predator-prey relationship

As the wolves prey on the moose, the moose population _________

moose wolf

0

60

30

0

1200

2400Wolf and Moose population on Isle Royale


As the wolves prey on the moose, the moose population decreases

moose wolf

0

60

30

0

1200



This decline is soon followed by _________in the wolf population

moose wolf

0

60

30

0

1200



This decline is soon followed by decreasein the wolf population

moose wolf

0

60

30

0

1200



This decline (of wolf) means the moose has fewer enemies and will therefore eventually ________

moose wolf

0

60

30

0

1200



This decline (of wolf) means the moose has fewer enemies and will therefore eventually increase

moose wolf

0

60

30

0

1200



This cycle continues indefinitely

moose wolf

0

60

30

0

1200


Density-dependent factors Parasitism and disease -

Density-dependent factors Parasitism and disease –

Example-

Density-dependent factors Parasitism and disease –

Example- eggs of parasitic wasp inserted beneath skin of larval moth (caterpillar)

Limits on growth Density-independent factors -

Limits on growth Density-independent factors – affect

all populations in similar ways, regardless of the population size


all populations in similar ways, regardless of the population size Examples -


all populations in similar ways, regardless of the population size Examples –

• Unusual weather



• Unusual weather• Natural disasters



• Unusual weather• Natural disasters• Seasonal cycles



• Unusual weather• Natural disasters• Seasonal cycles• Certain human activities



• Unusual weather• Natural disasters• Seasonal cycles• Certain human activities

• Damming rivers and clear-cutting forest

Density-independent factors Specific examples -

Density-independent factors Specific examples –

Storms or hurricanes


Storms or hurricanes • Insects that feed on plant buds and leaves

might be washed out by heavy rainstorms


Extreme cold or hot weather


Extreme cold or hot weather• Severe winter frost can kill many plants


Periodic droughts


Periodic droughts • Can affect entire populations of grasses

• Consumers in food web will then be affected

Human population growth

Human population growth In the United States and developed

countries, the current growth rate is ________


countries, the current growth rate is very low



In some developing countries, the human population growth is nearly _______



In some developing countries, the human population growth is nearly 3 people per second


• In some developing countries, the human population growth is nearly 3 people per second

• Because of this, the human population is well on its way to reaching ____________ in your lifetime


• In some developing countries, the human population growth is nearly 3 people per second

• Because of this, the human population is well on its way to reaching 9 billion in your lifetime

Human population growth For most of human existence, the

population grew ______


Agriculturebegins

Plowing And irrigation

Bubonicplague

IndustrialRevolution begins

Human population growth For most of human existence, the

population grew slowly


Agriculturebegins


Bubonicplague


Human population growth About 500 years ago, the population

began growing more rapidly because life was made easier by _______ and ______


Agriculturebegins


Bubonicplague


Human population growth About 500 years ago, the population

began growing more rapidly because life was made easier by agriculture and industry


Agriculturebegins


Bubonicplague


Human population growth With these advances, the human

population experienced ____________


Agriculturebegins


Bubonicplague


Human population growth With these advances, the human

population experienced exponential growth


Agriculturebegins


Bubonicplague


Human population growth Human population cannot keep growing

exponentially forever because


Agriculturebegins


Bubonicplague


Human population growth Human population cannot keep growing

exponentially forever because Earth and its resources are limited.


Agriculturebegins


Bubonicplague


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How populations grow