20 fish were marked. A second catch of 30 holds 6 marked. What is the estimated population?

Answer: ______________

When do ecologists choose mark and recapture over a quadrat?

• For still or slow life like grass
• For mobile animals like fish or beetles
• Only for trees

What does the mixing promise say?

• All animals stay in one corner
• Marked and unmarked mix fully, so the fraction matches everywhere
• Only marked animals may be recaught

Which of these breaks the method's promises?

• Many births between the two visits
• Using tiny harmless dye marks
• Keeping the gap between visits short

15 beetles were marked. A second catch of 40 holds 10 marked. What is the estimated population?

Answer: ______________

Marks make animals easier for predators to spot. What happens to the estimate?

• It inflates, since fewer marked return
• It shrinks to zero
• It stays exactly right

Lou computes 100 and announces exactly 100 fish live there. What is wrong?

• Fish cannot be counted
• The arithmetic uses the wrong operation
• The result is an estimate, good only as far as its promises hold

A team recatches only at the exact release spot, with no time to mix. What happens to the estimate?

• It stays perfect
• It drops too low, since the marked share looks bigger than it is
• It doubles exactly