Carrying Capacity

2.4-2.7

Abiotic and Biotic Factors Work Together to Influence Population Size

• The growth of individuals and increase in size of populations is regulated by available resources.

• Resources are limited.• Competition for food or other

resources may take a toll on populations.

• Environmental stress, such as heat or cold, will also limit population size.

• The greatest number of individuals that a space can support is called its carrying capacity.

• The carrying capacity determines the population’s maximum size.

• Homeostasis is the tendency for a population to remain stable.

• Populations will remain between the upper and lower limits that are defined by mortality, birthrate, and population movements.

Population Density May Fluctuate

• The interaction of the population’s growth rate with the environment determines the density of the surviving population.

• If you measure the density of a population at different times during the year, you will seldom find any two consecutive measurements that are the same.

Populations May Spread to Neighboring Areas

• The ability of populations of living things to spread from a central place into others is called dispersal.

• This can be either active or passive.

• Organisms must be able to survive and reproduce in the new location.

Barriers Can Prevent Dispersal• Most species have a limited

geographic range.• Physical barriers such as mountains

and water prevent dispersal.• An increase in a population of

organisms that can move encourages emigration to less populated areas that my have resources.