Population dynamics
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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. Population Dynamics. Why does it matter?.

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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

Population Dynamics


Why does it matter
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
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
Why does it matter? …more examples

  • Insect pests?

    • Can wipe out crops

  • Introduced species can destroy an entire ecosystem.

    e.g. Caulerpa taxifolia



Population dynamics

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)

Limiting factors…


Population dynamics

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 factors1

Density dependent growth was not too severe.

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.

Limiting factors



What is the human carrying capacity for earth1

Assuming current trends… growth was not too severe.

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 earth2
What is the human carrying capacity for earth? growth was not too severe.

  • 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 growth was not too severe.

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

World population depends largely on…