Limits to Growth Study Notes

2.2 Limits to Growth

History of Easter Island

Easter Island Carrying Capacity

  • The peak carrying capacity of Easter Island was estimated to be between 9,000 and 15,000 individuals.

  • The most recent population size is reported to be between 2,000 and 3,000 individuals.

  • Attention is drawn to the question: What changed that led to this decline in carrying capacity?

Limiting Factors

Density-Independent

Density-Dependent

Learning Objectives

  • Identify factors affecting carrying capacity.

  • Identify limiting factors that depend on population density.

  • Identify limiting factors that do not depend on population density.

  • Explain the relationship between limiting factors and population extinction.

Vocabulary

  • Limiting Factor: A variable that can restrict the growth, abundance, or distribution of an organism or a population.

  • Density-Dependent Limiting Factor: A factor that influences a population in ways that vary based on population density.

  • Density-Independent Limiting Factor: A factor that influences a population regardless of its density.

Limiting Factors and Carrying Capacity

  • Limiting factors are critical determinants of the carrying capacity of an environment for a species.

  • There are two primary categories of limiting factors: density-dependent and density-independent.

  • An example question arises: What is the limiting factor for the steelhead trout? What other abiotic factors might limit their population?

Density-Dependent Factors

  • Definition: Density-dependent limiting factors exert greater influence when a population reaches a certain density.

  • Key Examples:
      - Competition:
        - Increased individuals lead to quicker depletion of resources.
        - Competition may occur for food, water, space, sunlight, shelter, mates, and territories.
      - Parasitism and Disease:
        - High density facilitates rapid spreading of parasites and diseases among host populations.
        - Stress due to overcrowding may contribute to decreased birth rates, increased death rates, and heightened emigration rates.
      - Predation: The interaction between predators and prey affects population dynamics, exemplified by a specific case of wolf and moose populations on Isle Royale.

Predator-Prey Relationships

  • Example: Wolf and Moose Populations on Isle Royale   - Population graphs exhibit trends of moose and wolf populations from 1955 to 2005, reflecting cyclical relationships influenced by external factors such as disease outbreaks (e.g. CPV outbreak).

Herbivore Effects

  • Explains the cyclical nature of herbivore and plant populations, similar to predator-prey dynamics.

Density-Independent Factors

  • Definition: Density-independent limiting factors affect populations regardless of their size and density.

  • Examples:
      - Natural Disasters: Hurricanes, droughts, floods, wildfires.   - Weather Conditions: Extreme weather may also impact population survival and reproduction rates.

Impact of Limiting Factors on Extinction

  • If the carrying capacity declines significantly, populations may face extinction, underlining the critical nature of limiting factors.

Population Dynamics

  • Example: Meerkat Population Dynamics as illustrated in "The Wonderful World Of The Kalahari" discussing their behaviors and population dynamics, highlighting benefits or detriments of population interactions.

Hypothetical Scenario

  • Question Raised: What would occur if humans behaved like animals? Inviting exploration of the comparison between human and animal behavior dynamics.