Investigating Animal Abundance: Capture-Recapture for Biologists

Case studies 87 Field Fig. 5.2 Drosophila study-site with trap positions marked ( • ).this is the same as the point of capture itself.This is the case whenever capture depends on the activity of the investigator.When capture depends on the activity of the animal itself, however, there are two alternatives.The animals from a trap can either be released at the location of the trap itself, on the assumption that, their true prior position being unknown, the trap's location represents their 'mean' position; or they can be released at random throughout that trap's area of influence.The disadvantages of the second alternative are the time it takes, and the fact that each individual will probably be replaced at a position quite different from that prior to capture.The advantages are that individuals as a group will be redistributed approximately as ' before, and unnatural over-crowding will be avoided.