HIGHER-PLANT TERPENOIDS - A PHYTOCENTRIC OVERVIEW OF THEIR ECOLOGICALROLES

Characteristics of higher plant terpenoids that result in mediation of numerous kinds of ecological interactions are discussed as a framewor k for this Symposium on Chemical Ecology of Terpenoids. However, the r ole of terpenoid mixtures, either constitutive or induced, their intra specific qualitative and quantitative compositional variation, and the ir dosage-dependent effects are emphasized in subsequent discussions. It is suggested that little previous attention to these characteristic s may have contributed to terpenoids having been misrepresented in som e chemical defense theories. Selected phytocentric examples of terpeno id interactions are presented: (1) defense against generalist and spec ialist insect and mammalian herbivores, (2) defense against insect-vec tored fungi and potentially pathogenic endophytic fungi, (3) attractio n of entomophages and pollinators, (4) allelopathic effects that inhib it seed germination and soil bacteria, and (5) interaction with reacti ve troposphere gases. The results are integrated by discussing how the se terpenoids may be contributing factors in determining some properti es of terrestrial plant communities and ecosystems. A terrestrial phyt ocentric approach is necessitated due to the magnitude and scope of te rpenoid interactions. This presentation has a more broadly based ecolo gical perspective than the several excellent recent reviews of the eco logical chemistry of terpenoids.