Limits to Growth

Learning Objectives Identify factors that determine carrying capacity. Identify the limiting factors that depend on population

density. Identify the limiting factors that do not depend on

population density.

Limiting Factors

Limiting factors determine the carrying capacity of an environment for a species.

Density dependent Density independent

Density-Dependent Factors

Density-dependent limiting factors operate strongly when population density reaches a certain level.

Competition

• More individuals use up resources sooner.

• Individuals may compete for food, water, space, sunlight, shelter, mates, territories.

Predator–Prey Relationships

Herbivore Effects

Populations of herbivores and plants cycle up and down like populations of predators and prey.

Parasitism and Disease

• Parasites and diseases can spread quickly through dense host populations.

• Stress from overcrowding can lead to lower birth rates, higher death rates, and higher emigration rates.

Density-Independent Factors

Density-independent limiting factors affect all populations regardless of population size and density.

Density-Independent Factors

• Examples: hurricanes, droughts, floods, wildfires

• Density-independent factors may actually vary with population density.

Canyon Lake, TX

Controlling Invasive Species

Density-independent measures?• Herbicides, mechanical removal

Density-dependent measures? • Predation

Expensive, temporary

Another invasive species?

Salvinia

Overview: Limits to Growth

Density dependent

Density independent

Flood waters cover a field of wildflowers.

Non-native snakes released into a wetland prey on native rodents.

Flu virus spreads quickly in schools.

Wildfires spread through a grassland.