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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