Population Growth Notes

Population growth depends on two things

1. Biotic potential - this is the number of offspring that an organism can produce

2. Environmental Resistance - this is the combination of factors which limit the growth of a population.

Biotic Potential                                    Environmental Resistance

- reproduction rate                                 - lack of food

- ability to migrate                                 - lack of water

- ability to invade new habitats             - no habitat

- defense mechanisms                           - harsh weather

- ability to cope with harsh conditions  - predators

                                                               - disease

                                                               - temperature extremes

                                                               - parasites

                                                               - competition

When the biotic potential increases or the environmental resistance decreases, a population explosion results.

Humans have mostly overcome environmental resistance and so we are in a population explosion.

Population growth can be calculated. It depends on four factors

1. births - the number of individuals born in a population

2. deaths - the number of individuals which die in a population

3. immigration - the number of individuals which enter an area

4. emigration - the number of individuals which leave an area

population growth = (births + immigration) - (deaths + emigration)

                                    initial # of organisms

Five factors tend to keep populations balanced

1. predator-prey relationships - if predators eat to many prey, the prey population will decrease and then so will the predator population. When the predator population decreases, fewer prey are eaten and the prey population increases again. This increase allows the predator population to increase.

2. plant-herbivore relationship - same as predator-prey

3. host-parasite relationship - same as predator-prey

4. carrying capacity - if the population becomes too large, the ecosystem cannot support it and it decreases again. When the ecosystem recovers, the population can grow again.

5. territoriality - some species defend a territory of a certain size. This limits the number of individuals which can live in a given area.