[GHS Ecobiology]


One female herring (a small fish) can lay one million eggs in a single year. If all the eggs hatched and all the offspring survived, what would soon happen to the earth? The fish would overpopulate the world and they would then deplete the resources they need. Other animals would be affected, and perhaps, eventually, many species would die off.

Population: A group of individuals of the same species (humans, tigers, dandelions, bacteria, etc) that live in a particular area.

Birth and immigration add to a population.

Death and emigration subtract individuals to a population

Immigration: Individuals moving into an area

Emigration: Individuals moving out of an area

What causes creatures to immigrate/emigrate? Lack of resources (food, water shelter), lack of mates, lack of breeding territory, poor weather, too many predators, etc..

Population Increases when:

# of births + # of immigrants > # of deaths + # of emigrants

Population Decreases when:

# of deaths + # of emigrants > # of births + # of immigrants

Most organisms produce more offspring than can survive to grow up and reproduce. Why do they need to produce so many young? To ensure that some survive to breeding age!

Biotic Potential: The rate at which a population would grow if every new individual survived to adulthood and reproduced at its maximum capacity.

When a population grows at its maximum rate, it does so exponentially. This is shown by a J-shaped curve on a graph (see graph at right).

Some biotic potentials:

Humans = 6% per year (population doubles every 11 years)

Rats =1.5% per day (400% per year) (pop. doubles every 47 days)

Bacteria = 250 % per hour (doubles every 15-30 minutes)