[The conflict between optimisation and orderliness in building behaviour of the caddis fly, Chaetopteryx villosa Fabr.(Limnephilidae: Trichoptera), larvae].
The Optimal Foraging Theory predict that an animal should restrict its searching activity to those patches of environment, where the ratio of gain to time and energy spent is maximal. Experimenters usually verify the prediction against the null hypothesis of random activity distribution between patches. As animals always prefer profitable patches to some degree, experimental results can always be interpreted as confirmation of the theory. In opposite to this approach, we put forward the "regularity hypothesis". According to this hypothesis, the finding of a profitable item in some patch makes an animal to stay and test more items within the patch. The readiness to test decreases if the profitability of these items is low, and the animal eventually leaves the patch. It also searches in other patches less carefully. As a result, positive and negative responses to items are repeated by ordered series. In general, this regularity of responses helps animals to choose profitable patches. However, animals may also ignore some profitable patches because of the regularity, so that the behavioural optimazation fails. The regularity hypothesis have been tested in experiment with the search of building material and patch choice by caddisfly larvae. The first of two experimental patches contained egg shell fragments (profitable building material) mixed with a sand (unprofitable). The second patch contained sand only. Larva stayed within the first patch after a shell had been found, so that the probability to find more shells increased. However, larvae started walking after they had found several sand particles. Once starting to walk, they found new shell fragments and tested them, but tended to reject them and eventually leave the patch. Moreover, upon returning to the first patch, larvae also might reject fragments and leave the patch again. Rejections are accounted for by the fact that the duration of testing was too short to identify fragments correctly. As a result, negative responses were repeated to a certain degree independently of the profitability of building material, and the patch choice was not optimal. These results are agreed with the regularity hypothesis. It is argued that the hypothesis can be used as an alternative to the Optimal Foraging Theory.
Nepomniashchikh
V A
VA
Institute for Biology of Inland Waters, Russian Academy of Sciences, Borok, Yaroslavskaja obl. 152742, Russia. nepom@ibiw.yaroslavl.ru
D000818:Animals; D001522:Behavior, Animal; D007313:Insecta / Q000502:physiology*; D007814:Larva / Q000502:physiology