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Flashcards · Biology · Monitoring and Maintaining the Environment

Estimating Population Size

17 cards

  1. What do you multiply the mean per quadrat by to scale up?

    The number of quadrats that would fit in the whole area.

  2. How do you find how many quadrats fit in the area?

    Total area divided by the area of one quadrat.

  3. What is the area of a 0.5 m by 0.5 m quadrat?

    0.25 square metres.

  4. A mean of 4 per 0.25 m squared quadrat: how many per square metre?

    16.

  5. When is capture-recapture used?

    To estimate the population of animals that move about.

  6. What happens to the animals in the first sample?

    They are counted, marked and released.

  7. Why wait before the second sample?

    So the marked animals can mix with the rest of the population.

  8. What is counted in the second sample?

    The total number caught, and how many of them are marked.

  9. State the capture-recapture equation.

    Population = (first sample × second sample) ÷ number of marked animals in the second sample.

  10. Give a harmless way to mark a snail.

    A small dot of non-toxic paint on the shell.

  11. Name two assumptions of capture-recapture.

    No births, deaths or movements between samples, and the marks stay on and are harmless (any two).

  12. What is the effect if marks rub off?

    Fewer marked animals are found, so the population is overestimated.

  13. Why do small samples give less reliable estimates?

    A small change in the number counted has a big effect on the estimate.

  14. Why does a patchy habitat cause errors with quadrats?

    The quadrats may land on more patches or fewer patches than average.

  15. How can the estimate be made more reliable?

    Use larger samples or more quadrats, and repeat and take the mean.

  16. Why do fisheries use capture-recapture?

    To estimate fish numbers so that they can set sustainable catches.

  17. Three stages of capture-recapture shown with beetles, with no labels. Describe what is done at each of steps 1, 2 and 3, and how the population size is found. The same three stages with every part labelled.

    1 Catch 20 animals, mark them and release them. 2 Wait for them to mix with the population. 3 Catch another sample, of 30, and count those that are marked, which is 6. Population = 20 × 30 ÷ 6 = 100.