On a population graph, the carrying capacity is represented by a flat line

• May also be a small "wave"

• Follows a period of exponential growth; a J-shaped curve where the population keeps increasing

• The line represents population size, so it decreases in response to a limiting factor

Limiting factors are any factor that reduces or the size of a population or keeps it from increasing

• May be a resource, another species, the environment, etc.

• Example: food is a limiting factor because you can't have more individuals than food to feed them

Limiting factors that DO NOT depend on population size are called density-independent

• Include climate, weather, natural disasters, and pollution

• Affect all populations the same, whether they are large or small

Limiting factors whose effect depends on the size of the population are called density-dependent

• Includes natural resources (food, water, space), diseases, and predators

• Tend to have a greater effect on large, dense populations because of increased competition and more opportunity to attract predators and disease

Keystone Species

A keystone species is an organism that helps define an entire ecosystem. 

Without its keystone species, the ecosystem would be dramatically different or cease to exist altogether.

The removal of a keystone species REDUCES the BIODIVERSITY of the ecosystem.

Keystone Examples

The keystone species in this habitat is the sea otter.

The sea otter eat urchins and therefore keep the population of sea urchins low. Sea otters also build dams which create wetlands for other organisms to live in.

Without sea otters, sea urchins over populate and eat all of the kelp. Wetlands are destroyed and biodiversity decreases.