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.Habitat Temperature, 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 Competition Character Displacement

Interspecific Competition Character 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