Comment les peuplements de plantes et d’insectes phytophages se façonnent mutuellement : la théorie coévolutive de la structure des peuplements

Abstract

A plant community may be considered as an assemblage of species whose chemical defenses against herbivores are more or less efficient. In the same way a community of phytophagous insects can be viewed as a group of consumers which are capable either of bypassing the plants’ chemical defenses, or of taking advantage of them. The inter-relations between the two communities result in an array of compromise solutions originating from the coevolution of plants and insects. The pros and cons of such a coevolutionary theory of community structure are discussed. Particular attention is given to the following points : the concept of community structure, the major categories of toxiche-micals and digestibility-reducing substances involved in the «arms race» between plant producers and animal consumers, the evolutionary mechanisms implied in coevolution, the costs and benefits of the alternative adaptive strategies adopted by insect consumers (with particular emphasis on their bioenergetic implications), and the dynamic aspect of coevolution. Whereas coevolution undoubtedly plays a role in plant-insect interactions, such a role should not be overemphasized. The well documented case of the moths living on various oak species highlights some obvious inconsistencies. Thus the coevolutionary theory of community structure should still be considered more as a useful working hypothesis rather than a well established fact.