THE BEHAVIORAL BASIS OF APOSTATIC SELECTION BY HUMANS SEARCHING FOR COMPUTER-GENERATED CRYPTIC PREY

Apostatic selection (preference for common prey) has been demonstrated in several experiments on a variety of predators, but its behavioural basis is largely unknown. A computer program was written to generate (on a monochrome monitor) cryptic ‘prey’ of two types differing in their shape. Human subjects were presented random sequences of 45 ‘frames’ of backgrounds, of which 15 were devoid of prey and 30 contained a single prey which could be either of the two types. One group of 10 subjects was presented with five frames of prey 1 and 25 of prey 2, a second group received 15 of each and a third 25 of prey 1 and five of prey 2. The subjects had to decide as quickly as possible whether or not a prey item was present (and, if so, which type) and to press the appropriate key before proceeding to the next frame. Overall, selection was apostatic and was probably caused by differential search image development resulting from different encounter rates with common and rare forms. There was no evidence for search image ‘interference’. Copyright © 1993 The Association for the Study of Animal Behaviour.