Population Dynamics and Human Population. Part I: Population Dynamics.
Population Dynamics
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Transcript of Population Dynamics
Population Dynamics• Changes in a population
– How do we define a population?
• Population– Individuals of a
single species– Occupy the same
area– Rely on the same
resources– Affected by same
environmental factors
– Interact and breed
Why does it matter?• How long does it take bacteria to
proliferate into the millions?– E. coli can double in less than 20 minutes
• Can reach many millions in a few hours
If the environment is not ideal
• How does our body affect bacterial growth?– with wbc, release specific
protein, stimulates a hormone that raises body temp
• How do treatments (antibiotics) affect bacterial growth?– Alters or poisons their
environment…halts growth
Why does it matter? …more examples
• Insect pests?– Can wipe out
crops
• Introduced species can destroy an entire ecosystem.
e.g. Caulerpa taxifolia
What about human populations?
• Linear growth– Example--
2,4,6,8,10,12,14,....– Produces a linear graph.– Doubling occurs relatively
slowly.
• Exponential growth– Example--2, 4, 8, 16, 32,
64, 128....– Produces an exponential
(logarithmic) graph--a "J" curve.
– Doubling occurs rapidly.– Populations tend to grow
exponentially, when there are no limits to growth.
Limiting factors…• produce
environmental resistance
• converts a "J" curve to an "S" curve= logistic growth
e.g. space and hunting restricted elephant seals
& sets the carrying capacity (environmt. support)
Population may stabilize if resources are renewable, and growth was not too severe.
Population may crash if resources are non-renewable or if growth outpaces renewal.
Limiting factors
• Density dependent– Factors that limit
growth more severely as the population increases
– Biotic– E.g. food, nutrients,
disease, etc.
• Density independent– Factors that effect
population in a consistent way whether there are few or many individuals.
– Abiotic– E.g. weather, climate,
etc.
What is the human carrying capacity for earth?
Assuming current trends…10-12 billion
Low range est.– At U.S. dietary
standards.... 1.2 billion– At U.S. energy
consumption.... < 1 billion
What is the human carrying capacity for earth?
What is the human carrying capacity for earth?
• High range estimates… 45 billion or more if the following conditions met.
– Cultivating all arable land– Mass conversion to nuclear power & renewable
resources • what do we do with spent fuel?
– Expansion of mining, perhaps to crustal depths of 1 mile.
• These high estimates assume technologies that do not yet exist.
– Some estimate that the carrying capacity could be as much as 157 billion if the population shifted to a grain diet.
World population depends largely on…
• Regional differences– Sweden very stable
• Birth rates– E.g. 28 births per 1000
people
• Death rates– E.g 11 deaths per 1000
people
Today’s rates?Zero population growth (ZPG)birth rates = death rates