UNIT 3.4 ~ Carrying Capacity 

Carrying Capacity (k):

  • the max. Number of individuals in a pop. that an ecosystem can support (based on limiting resources)

Carrying Capacity (k)

  • Highest pop. size an ecosystem can support based on limiting resources:   * Food   * Water   * Habitat (nesting sites, space)
  • Overshoot:   * when a population briefly exceeds carrying capacity     * Ex: deer breed in fall, give birth all at once in spring; sudden spike in pop. = overshoot
  • Consequence of overshoot:   * resource depletion ex: overgrazing in deer
  • Die-off:   * sharp decrease in pop. size when resource depletion (overshoot) leads to many individuals dying     * Ex: many deer starve with too many new fawns feeding in spring

Die-off Example

  • Reindeer of St. Paul Island   * 25 introduced in 1910   * Growth was gradual (10’-30’), then exponential (30’-37’)   * Carrying capacity was overshot   * Sharp die-off lead to pop. crash as food resource (lichen) were severely depleted
  • Real pops. don’t always fluctuate around carrying capacity. If resource depletion is severe enough, total pop. crash can occur

Predator-Prey

  1. Hare pop. increase due to low predator pop. (lynx)
  2. Lynx pop. increase due to increase in food (hare)
  3. Increasing lynx pop. limits hare pop; leads to die-off
  4. Hare die-off decreases lynx food source, leading to die-off
  5. Hare pop. increase due to low predator pop. (lynx)

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