Population size

• What is population size?

  Number of organisms in a specific area
• How can population size be estimated from a small sample area?

  By scaling up from quadrat counts
• What are the steps to estimate population size using quadrats?

  1. Count organisms in quadrats
  2. Divide habitat area by quadrat size
  3. Multiply by mean number of organisms per quadrat
• If a quadrat has an area of $0.5 \text{ m}^2$ and the habitat area is $800 \text{ m}^2$, what is the first step to estimate population size?


  Divide $800 \text{ m}^2$ by $0.5 \text{ m}^2$
• How do you calculate the estimated population of daisies in the field?

  Multiply $1600$ by $10$
• What is the capture-recapture method for estimating animal populations?

  1. Capture a sample of the population
  2. Mark the animals harmlessly
  3. Release them back
  4. Recapture another sample
  5. Count marked individuals
  6. Use the equation to estimate population size
• What is the first step in the capture-recapture method?

  Capture a sample of the population
• How many woodlice were caught in the second sample?

  35 woodlice
• How many marked woodlice were recaptured?

  5 marked woodlice
• What is the equation to estimate population size in the capture-recapture method?

  Population Size = (first sample × second sample) ÷ marked
• What assumptions must be made when using the capture-recapture method?

  • Marking does not affect survival
  • No immigration or emigration
  • Population size remains constant
• If a field has an area of $1200 \text{ m}^2$ and a quadrat size of $0.25 \text{ m}^2$, what is the first step to estimate tulip population?


  Divide $1200 \text{ m}^2$ by $0.25 \text{ m}^2$
• How do you estimate the total population of tulips in the field?

  Multiply the area by mean per quadrat
• What is the formula for estimating population size using capture-recapture?

  Population Size =

  \[

  \frac{\text{number in first sample} \times \text{number in second sample}}{\text{number in second sample previously marked}}

  \]