(Capture) mark – release – recapture

Step 1.Capture a sample of organisms.

Note: ensure the technique for trapping them matches the organisms being studied e.g.

Pitfall trap for crawling insects Longworth trap for small mammals

(Capture) mark – release – recapture

http://www.liverpoolmuseums.org.uk/wml/naturalworld/bughouse/shed.asp

Step 2.Mark the animals in some way.

Note: ensure the technique matches the organisms being studied e.g.

Nail varnish blobs on the back of beetles

Tags in small mammals ears Rings for birds

(Capture) mark – release – recapture

Step 3.Release the animals.

(Capture) mark – release – recapture

Step 4.Recapture a second sample and count the number of marked individuals.

Note: ensure the animals had time to mix with the rest of the population before capturing again.

(Capture) mark – release – recapture

Step 6.Estimate population size using the formula.

(Capture) mark – release – recapture

(Capture) mark – release – recapture

Assumptions.

The # of organisms in the population does not change between samples. Marked animals mix randomly with the rest of the population. Trapping and marking do not affect the animals in any way.

Objective Estimates– Absolute estimates - numbers/unit area

• techniques– capture – recapture (mark-release-recapture)

» capture animals, mark, release, recapture; determine proportion of marked and from this make total population estimate

» major assumptions:» (i) marking doesn't affect animals (behaviorally, physiologically, or ecologically)» (ii) marked animals are completely mixed in population» (iii) probability of capturing a marked animal is the same as capturing an

unmarked animal (closed population)» (iv) marked animals don't lose their marks» (v) marked mix naturally with unmarked» (vi) some other assumptions

Mark-Recapture Study

•Capture, mark and release 64 monarch butterflies

•Capture monarchs at a later date. The number captured was 98 of which 22 were marked

•The population size is estimated to be 285 butterflies