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How populations grow Population density – number of individuals living in a defined space
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How populations growChapter 14 – Notesheet II
14-3 – population density & distribution
14-4 – population growth curves
How populations grow Population density –
How populations grow Population density – number of
individuals living in a defined space
How populations grow Population density – number of
individuals living in a defined space # of individuals
area (units2)
How populations grow Population density – number of
individuals living in a defined space # of individuals
area (units2)• example of low density• example of high density
How populations grow Population dispersion -
How populations grow Population dispersion – way in which
individuals of a population are spread in an area or a volume
How populations grow Population dispersion – way in which
individuals of a population are spread in an area or a volume
How populations grow Survivorship curve -
How populations grow Survivorship curve – generalized
diagram showing the number of surviving members over time from a measured set of births.
How populations grow Survivorship curve
type 1 -- common among large mammals; low level of infant mortality;
high level of parental care for young
How populations grow Survivorship curve
type 2 – birds, small mammals, and some reptiles; survivorship is roughly equal at all points in
organisms life – just as likely to live as to die
How populations grow Survivorship curve
type 3 – invertebrates, fish, amphibians, and plants; very high birth
rate and infant mortality rate; many offspring die
from predation; low level of parental care for young
Population Growth Curves Immigration -
Population Growth Curves Immigration – the movement of
individuals into a population from another population
Population Growth Curves Immigration – the movement of
individuals into a population from another population Example -
Population Growth Curves Immigration – the movement of
individuals into a population from another population Example -animals in search of mates or
food arrive from outside the population
Population Growth Curves Emigration -
Population Growth Curves Emigration – movement of
individuals out of a population and into another population
Population Growth Curves Emigration – movement of
individuals out of a population and into another population Example -
Population Growth Curves Emigration – movement of
individuals out of a population and into another population Example – young animals approach
maturity and leave area to establish new territories
Population Growth Curves Exponential growth -
Population Growth Curves Exponential growth – occurs when a
population size increases dramatically over a period of time
Exponential growth A graph of exponential growth would
be
Exponential growth A graph of exponential growth would
be J-shaped
Exponential growth A graph of exponential growth would
be J-shaped Example -
Exponential growth A graph of exponential growth would
be J-shaped Example – bacteria, rabbits in Australia
Exponential growth A graph of exponential growth would
be J-shaped Example – bacteria, rabbits in Australia
• Usually occurs
Exponential growth A graph of exponential growth would
be J-shaped Example – bacteria, rabbits in Australia
• Usually occurs under ideal conditions with
Exponential growth A graph of exponential growth would
be J-shaped Example – bacteria, rabbits in Australia
• Usually occurs under ideal conditions with unlimited resources
Exponential growth Bacteria - some are able to
reproduce every 20 minutes
Exponential growth Bacteria - some are able to
reproduce every 20 minutes If you begin with one bacteria
Exponential growth Bacteria - some are able to
reproduce every 20 minutes If you begin with one bacteria
• 20 minutes later there will be 2
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 __
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
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 ___
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 ___
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 ___
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 ___
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
How population grow Logistic growth – occurs when a
population’s growth slows or stops following a period of exponential growth Why might this happen?
How population grow Logistic growth – occurs when a
population’s growth slows or stops following a period of exponential growth Why might this happen?
• Birthrate decreases
How population grow Logistic growth – occurs when a
population’s growth slows or stops following a period of exponential growth Why might this happen?
• Birthrate decreases• Deathrate increases
How population grow Logistic growth – occurs when a
population’s growth slows or stops following a period of exponential growth Why might this happen?
• Birthrate decreases• Deathrate increases• Or both events occur at same time
How population grow Logistic growth – occurs when a
population’s growth slows or stops following a period of exponential growth Why might this happen?
• Birthrate decreases• Deathrate increases• Or both events occur at same time
Logistic growth Graph would be
“S-shaped”
Time (hours)
Number of yeast cells
Logistic growth Graph would be
“S-shaped” Initial growth
would be ___
Time (hours)
Number of yeast cells
Logistic growth Graph would be
“S-shaped” Initial growth
would be slow, followed by a period of ___
Time (hours)
Number of yeast cells
Logistic growth Graph would be
“S-shaped” Initial growth
would be slow, followed by a period of rapid growth
Time (hours)
Number of yeast cells
Logistic growth Graph would be
“S-shaped” Initial growth
would be slow, followed by a period of rapid growth
Growth then___ Time (hours)
Number of yeast cells
Logistic growth Graph would be
“S-shaped” Initial growth
would be slow, followed by a period of rapid growth
Growth then levels off
Time (hours)
Number of yeast cells
Logistic growth Caused by some
sort of __________________ on the
population.
Time (hours)
Number of yeast cells
Logistic growth Caused by some
sort of limitingfactor on the
population.
Time (hours)
Number of yeast cells
Logistic growth Carrying capacity -
Time (hours)
Number of yeast cells
Logistic growth Carrying capacity -
the largest number of individuals that a given environment can support
Time (hours)
Number of yeast cells
Logistic growth Carrying capacity -
What if conditions
change?
Time (hours)
Number of yeast cells
Logistic growth Carrying capacity -
What if conditions
change? The carrying
capacity will also change
Time (hours)
Number of yeast cells
Logistic growth Carrying capacity -
Where is carrying
capacity on “S” shaped curve?
Time (hours)
Number of yeast cells
Logistic growth Carrying capacity -
Where is carrying
capacity on “S” shaped curve?
Time (hours)
Number of yeast cells
Carrying capacity
Limits on growth Population crash -
Limits on growth Population crash – a dramatic
decline in the size of a population over a short period of time
Limits on growth Population crash – a dramatic
decline in the size of a population over a short period of time Example -
Limits on growth Limiting factors -
Limits on growth Limiting factors – a factor that
causes population growth to decrease
Limits on growth Limiting factors – a factor that
causes population growth to decrease Examples -
Limits on growth Limiting factors – a factor that
causes population growth to decrease Examples –
• competition
Limits on growth Limiting factors – a factor that
causes population growth to decrease Examples –
• Competition• predation
Limits on growth Limiting factors – a factor that
causes population growth to decrease Examples –
• Competition• Predation• Parasitism and disease
Limits on growth Limiting factors – a factor that
causes population growth to decrease Examples –
• Competition• Predation• Parasitism and disease• Drought and other climate extremes
Limits on growth Limiting factors – a factor that
causes population growth to decrease Examples –
• 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 _________
Limits on growth Density-dependent factors –
Growth rate decreases as density increases
Density-dependent factors Competition
Density-dependent factors Competition
Members of population compete with one another for resources such as food and shelter
Density-dependent factors Competition
Members of population compete with one another for resources such as food and shelter
As populations become denser, the resources are used up, limiting how large the population can grow
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
Density-dependent factors Predation – predator-prey relationship
As the wolves prey on the moose, the moose population decreases
moose wolf
0
60
30
0
1200
2400Wolf and Moose population on Isle Royale
Density-dependent factors Predation – predator-prey relationship
This decline is soon followed by _________in the wolf population
moose wolf
0
60
30
0
1200
2400Wolf and Moose population on Isle Royale
Density-dependent factors Predation – predator-prey relationship
This decline is soon followed by decreasein the wolf population
moose wolf
0
60
30
0
1200
2400Wolf and Moose population on Isle Royale
Density-dependent factors Predation – predator-prey relationship
This decline (of wolf) means the moose has fewer enemies and will therefore eventually ________
moose wolf
0
60
30
0
1200
2400Wolf and Moose population on Isle Royale
Density-dependent factors Predation – predator-prey relationship
This decline (of wolf) means the moose has fewer enemies and will therefore eventually increase
moose wolf
0
60
30
0
1200
2400Wolf and Moose population on Isle Royale
Density-dependent factors Predation – predator-prey relationship
This cycle continues indefinitely
moose wolf
0
60
30
0
1200
2400Wolf and Moose population on Isle Royale
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
Limits on growth Density-independent factors – affect
all populations in similar ways, regardless of the population size or density Examples -
Limits on growth Density-independent factors – affect
all populations in similar ways, regardless of the population size or density Examples –
• Unusual weather
Limits on growth Density-independent factors – affect
all populations in similar ways, regardless of the population size or density Examples –
• Unusual weather – periodic drought can affect the entire population of grass – and ultimately the food web
Limits on growth Density-independent factors – affect
all populations in similar ways, regardless of the population size or density Examples –
• Natural disasters
Limits on growth Density-independent factors – affect
all populations in similar ways, regardless of the population size or density Examples –
• Natural disasters – volcanoes, tsunamis, tornados, and hurricanes can wipe out populations regardless of density
Limits on growth Density-independent factors – affect
all populations in similar ways, regardless of the population size or density Examples –
• Human activities
Limits on growth Density-independent factors – affect
all populations in similar ways, regardless of the population size or density Examples –
• Human activities – threaten habitats by clearing forests, filling wetlands, polluting the air, land and water