Population Ecology and Growth Patterns

Learning Objectives

  • Population's Per-Generation Growth Rate:

    • Calculated using the net reproductive rate ($R_0$).

  • Predicting Population Growth:

    • Growth can be estimated using the per capita growth rate ($r$).

  • Types of Growth:

    • Exponential Growth: Growth without limitations, population increases rapidly.
    • Logistic Growth: Growth that slows as population reaches carrying capacity, primarily due to resource limitations.

  • Population Size Limitations:

    • Density-Dependent Factors: Affect population based on density (e.g., competition, predation).
    • Density-Independent Factors: Affect population regardless of density (e.g., natural disasters).

  • Life History Strategies:

    • r-Selected Species: High reproductive rate, low competition ability (e.g., many insects).
    • K-Selected Species: Stable populations around carrying capacity (e.g., elephants).

  • Future Population Growth Predictions:

    • Based on age structure and total fertility rate.
    • Ecological footprint influence on Earth's carrying capacity for humans.

  • Key Terms:

    • Population: Group of individuals of the same species in a given area.
    • Carrying Capacity ($K$): Maximum population size the environment can sustain.
    • Exponential Population Growth: Growth without limits.
    • Logistic Population Growth: Growth that accounts for resource limitations.
    • Per Capita Growth Rate ($r$): Change in population size over time.
    • Net Reproductive Rate ($R_0$): Average number of offspring per individual.
    • Density-Dependent: Factors that vary with population size.
    • Density-Independent: Factors that are not affected by population size.

Factors Affecting Population Growth

  • Definitions:

    • Density: Number of organisms in a unit area.
    • Dispersion: How populations are spread (clumped, uniform, random).

  • Population Growth Rates:

    • Death Rates, Birth Rates: Key metrics in demographic studies.
    • Survivorship Curves: Graphical representation of the number of individuals surviving at each age.

Exponential vs. Logistic Growth

  • Exponential Growth:

    • Formula: \frac{dN}{dt} = r_{max} N
    • Assumes unlimited resources and ideal conditions.
    • Cannot be sustained indefinitely.

  • Logistic Growth:

    • Formula: \frac{dN}{dt} = rN \left(1 - \frac{N}{K}\right)
    • Incorporates carrying capacity ($K$).
    • Growth slows as population approaches $K$.

Life History Strategies

  • r-Selected Species:
    • Characteristics: Fast development, high reproductive rates, poor competitive ability.
  • K-Selected Species:
    • Characteristics: Stable populations, lower fecundity, high parental care.

Human Population Dynamics

  • Global Fertility Trends:

    • Fertility rates decline in many developed countries.
    • Population size affects resource sustainability.

  • Age-structure Pyramids:

    • Visual representations showing population distribution by age.
    • Useful in predicting future population trends.

Ecological Footprint and Sustainability

  • Ecological Footprint:
    • Measure of the demand on Earth's ecosystems.
    • Influences how many individuals can sustainably inhabit areas.