Community Ecology

Habitat :

  1. Defn: the resources and environmental conditions that a population requires.
    1. Resources include food and shelter
    2. Environmental conditions include abiotic factors and biotic factors such as competitors and predators.
  2. A habitat is specific for a species. Good Douglas squirrel habitat is not the same as good flying squirrel habitat.
  3. A species presence in a community is due to its tolerance to abiotic factors and biological interactions.

Niche :

  1. Defn: a specie's role in the community.
  2. Often means the species use of resources.
  3. Fundamental niche is the range of abiotic and biotic conditions where the organism could thrive.
  4. Realized niche is a smaller range forced by competition or predation.

Examples of specie interactions :

  1. Defn: interactions between populations of different species.
  2. Predation, herbivory, parasitism and disease - one species benefits at the cost of the other.
  3. Mutualism - both species benefit. Example: nitrogen fixing nodules on legume roots. Sometimes called symbiosis.
  4. Commensalism - One species benefits and the other suffers no harm or benefit.

Predator - Prey Interactions:

  1. Stable boom-crash cycle of prey and predator can develop.
  2. Interaction among species drives coevolution.
    1. Predators develop strategies. Example: bats use ultrasound to capture moths.
    2. Prey develop countermeasures.
      • Plants develop chemical and physical defenses against herbivores.
        1. Secondary compounds - distasteful chemicals.
        2. Enlisting aid. Example: acacia housing ants.
      • Animals develop chemical, physical and behavioral defense methods:
        1. Chemical: bombardier beetle
        2. Physical: camouflage:
        3. Physical: Batesian mimicry - tasty organism looks like a foul tasting organism.
        4. Physical: Mullerian mimicry - unpalatable species look alike.
        5. Behavioral: moths take evasive action when they hear bats approaching.

Community Structure

  1. Communities change over time.
  2. Succession is the 'repeatable' progression of communities that regrow on a site.
  3. Climax community probably doesn't exist.
  4. Species diversity decreases as towards the poles.
  5. Increased diversity increases ability to resist environmental change.
  6. Factors creating structure in a community:
    1. vegetation and trophic structures.
    2. affects of keystone predators
    3. competitive exclusion
    4. resource partitioning as evidence of past competition.