E. Ritualization of animal activities in relation to phylogeny, speciation and ecology: Reduction of ambiguity through ritualization

Abstract

Zoologists studying the social communication of animals have used the word ‘ritualization’ broadly speaking to describe changes in the signalling system during the course of evolution which have come about to make the signals more effective in evoking appropriate behaviour in a partner. (Critiques of different uses of the term in animal studies may be found in Blest (1961) and Wickler (1961).) Usually such signals operate within a species but some symbiotic relationships between different species also involve signals for which the word may reasonably be used (Baerends 1950). The chief emphasis in discussions of ritualization has been laid on evolutionary changes in form such as exaggerated amplitude of movement, alterations in frequency, increased regularity of rhythm, stereotyping of orientation, etc., besides the acquisition of morphological characters such as colours, soundproducing structures, to enhance the effectiveness of the signals. For signals to work the responding partner must of course be suitably tuned to them, but relatively little is known how well signal and responsiveness are matched (Marler 1961). Moreover, some ritualized signals may work, at least partly, through their general attention-catching properties rather than as the result of specifically evolved responsiveness, e.g. the red spot on the beak of an adult Herring Gull ( Larus argentatus ) makes the young peck at it for food partly through its mere contrast with the yellow beak (Tinbergen & Perdeck 1951). In addition, learning may play some role in the tuning of responsiveness to signals in natural situations, as can be seen in the development of inter-specific responses of species which consort (Bergman 1957). In spite of these uncertainties there is no doubt that with the evolution of much ritualized behaviour changes in responsiveness of the recipient have also evolved.