Ecological Theory of Population Distributions

The Concept of “Niche”

• Elton’s (1927)– Emphasized animal’s place in the biotic

community– What does the animal do for a living?

• Hutchinson’s (1957)– N-dimensional hypervolume– What environmental conditions does the critter

occupy?

But… Relationships Are Dynamic

• The environment is dynamic (i.e., changing)

• Site fidelity may prevent immediate response

• Animal’s may acclimate producing different responses

Factors Limiting Distributions

1. Mobility/dispersal

2. HabitatTemperature, moisture, light, oxygen, vegetation, aquatic/lithic substrates

3. Interactions with other animals

Limiting Factors – Dispersal

Limiting Factors – Dispersal(e.g., Westslope and Yellowstone Cutthroat)

Limiting Factors – Dispersal(e.g., Chihuahua Darter)

Limiting Factors - Habitat

• Temperature, Moisture, Light, Oxygen

• Vegetation, Aquatic or Lithic Substrates

Normal Response

Logistic Response

Limiting Factors – Other Organisms

• Intraspecific Interactions– Fretwell’s Ideal Free Distribution

– The Ideal Despotic Distribution

Limiting Factors – Other Organisms

• Interspecific Interactions– Competition

• Gause’s Competitive Exclusion– MacArthur (1958) northeastern warblers

• Character displacement

Interspecific CompetitionCharacter Displacement

Interspecific CompetitionCharacter Displacement – Darwin’s Finches

Limiting Factors – Other Organisms

• Predation

• Disease

Limiting Factor? or Factors?

• Leibig’s Law– Stressed importance of single factors limiting

distributions

• Does not work for interacting factors

A Final Note: Hierarchy of Scales