Searching for Cryptic Prey: The Effect of Search Rate

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Abstract
A model based on Holling''s (1959b) disc equation, of a predator searching for cryptic prey was developed. In doing so, it was assumed that the probability of a predator detecting an encountered prey item is inversely related to both prey crypticity and search rate. The optimal search rate will then reflect a trade-off between prey detection and the frequency of encounter. As prey become more cryptic this optimal search rate drops. If the energetic cost of locomotion is taken into account the optimal search rate is somewhat lower, but in general this additional effect is negligible. When a predator is searching for 2 prey types which differ in crypticity the optimal search rate increases with the relative density of the more conspicuous species. This increase in search rate may result in a dramatic drop in the probability of detecting the more cryptic prey, so that even when it is relatively abundant it may be virtually excluded from the diet. How this model can be modified to simulate the formation of a search image and generate density-dependent predation is discussed.