Post on 20-Dec-2015
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