Density Independent vs Density Dependent

My AP Biology ThoughtsUnit 8 Episode #28

Welcome to My AP Biology Thoughts podcast, my name is Morgan and I am your host for episode #28 called Unit 8 Ecology: Density Independent vs Density Dependent limiting factors.. Today we will be discussing exactly that, limiting factors in an ecosystem that are considered density independent and density dependent.

Segment 1: Introduction to Density Independent vs Density Dependent

Population density- the number of organisms within a given area or ecosystem (how crowded)

Low density ecosystems- organisms spread out (country/rural)

High density ecosystems- lots of organisms in little space (New York City)

Organisms can't grow exponentially or else the earth would be covered in all sorts of animals and population, so we need something that limits the population

Limiting Factor- something in an ecosystem that helps contain a population’s size by slowing or stopping growth, (biotic or abiotic)

Density dependent factors- higher the density of the population, the higher the impact of the limiting factor will be. When there are more organisms, more will be affected

Density independent- regardless of the density (crowdedness/ number of organisms) the limiting factor will decrease the population the same amount.

• large population and small population would be equally impacted

Segment 2: Example of density dependent and density independent limiting factors

What are these limiting factors?

Density dependent factors are food, shelter, water, parasites, and predators.

• There is competition for these resources so in a larger population, more animals are competing for these factors, and more animals will NOT have access to them
• A smaller population has less competition, and will not suffer as much from this lack of resources.

The same goes for parasites and predators.

• Big population has more prey for the predators to feed on and more animals the parasites can attach to
• A small population will not be as impacted by this type of limiting factor.

Density independent limiting factors - fire, flood, hurricanes, and pollution. natural disasters

• limit populations regardless of size

EXAMPLE: In a large or small ecosystem which has just experienced a hurricane, many of the organisms are going to die off, and the population size will decrease. If the hurricane kills 50% of the population, it is going to have the same impact in both ecosystems. Obviously with a larger...