KL

1-Determining-Population-Size

Lesson 1: Determining Population Size

Introduction to Population Size

  • Understanding how to determine population sizes is essential in ecology.

  • Helps in studying biodiversity, species health, and ecosystem dynamics.

Activity 1: Determining Population Size Like an Ecologist!

Purpose of the Activity

  • To introduce methods used by ecologists to estimate population sizes.

  • Hands-on experience with sampling techniques.

Methods for Determining Population Size

Method 1: Quadrats

  • A quadrat is a defined area used to sample populations.

  • Typically used for sessile or slow-moving organisms.

Method 2: Transect

  • Involves sampling along a straight line or path.

  • Suitable for assessing species distribution over a distance.

Method 3: Mark Recapture

  • A technique where animals are captured, marked, and released.

  • Later recapture of animals helps estimate population size.

Characteristics of Populations

Quantitative Measurements in Ecology

  • Ecologists use quantitative measurements to understand populations.

  • Important measurements include:

    • Population size

    • Density

    • Distribution

    • Life history

  • These metrics help reveal changes in population over time.

Population Size and Density

Definitions

  • Population Size (N): Total number of individuals in a specific area.

  • Population Density (D_p): Number of individuals per unit area or volume.

Estimating Population Size

  • Direct counting is impractical for large areas.

  • Sampling from subsets of populations provides estimates:

    • Techniques: transects, quadrats, mark-recapture.

    • Example: Estimating tree population in a forest.

Transects

Transect Sampling

  • A transect is a rectangular area along which species are counted.

  • Researchers walk the transect line, counting species within set distances:

    • 1 m for plants.

    • 50 m for mobile organisms.

  • Useful for sparse populations or large species.

Quadrats

Using Quadrats for Sampling

  • Quadrat: A fixed area for sampling a population.

  • Ideal for dense, immobile, or slow-moving organisms.

  • Procedure:

    • Randomly select several quadrats.

    • Count individuals within each quadrat.

Quadrats and Population Density

Calculating Population Density (D_p)

  • Formula:

    • D_p = N / A

    • Where N = total individuals in quadrats, A = total area of quadrats.

  • Extrapolation of total population:

    • Estimated Total Population = D_p × Total Area.

    • Example: Sampling white trilliums in a 10,000 m² area using four 1 m² quadrats with counts 5, 3, 2, and 1, giving an estimated population of 27,500 trilliums.

Sampling Using Mark-Recapture

Overview of Mark-Recapture Method

  • Involves trapping, marking, and releasing animals.

  • Proportion of marked to unmarked individuals data used for estimation.

Benefits of Mark-Recapture

  • Effective for highly mobile species (e.g., fish, birds).

  • Helps estimate population sizes in dynamic wildlife populations.

Mark-Recapture Example

Case Study of Warblers

  • Initial capture: 20 warblers marked and released.

  • Second capture: 50 warblers, with 10 being previously marked.

  • Calculation of population estimation:

    • Estimated population: 100 warblers based on capture proportions.