Chemically Mediated Multi-trophic Interactions

Abstract

In the Anthropocene, species loss is very well documented, but associated losses of genetic, functional, and multidimensional diversity are not so clear. Interaction diversity and phytochemistry are two axes of multidimensional and functional diversity that have been neglected in terms of understanding losses of diversity, but it is likely that major alterations to phytochemical variation among and within plant species has consequences for stability of biotic communities as well as ecosystem function. A great deal of research in ecology and evolution has examined chemical mediation of plant-animal interactions, and many of those studies have focused on plant compounds that reduce or deter insect damage and directly or indirectly affect secondary consumers. From these studies, it is clear that complex mixtures rather than specific molecules are often responsible for determining the outcomes of these trophic interactions as well as pollination, dispersal, competition, and other plant-animal interactions. Until recently, it has been difficult to generate and adequately analyze high quality data on phytochemical mixtures, rather the focus was on crude measures of broad classes of compounds or on well-studied compounds for which specific quantitative methods had been developed. In this chapter, we focus on two focal theoretical frameworks that drive investigations of chemically mediated interactions with a focus on mixtures: coevolution and trophic interaction theory. We briefly summarize relevant chemical and statistical approaches and present general questions for guiding empirical studies of complex mixtures and phytochemical variation. These questions and modern approaches to chemical ecology should contribute to substantially enhancing existing trophic interaction theory and to understanding the chemical losses that are occurring in ecosystems around the globe.