Foreword

The word ‘ubiquitous’ crops up repeatedly in this book in relation to trait-mediated indirect interactions (TMIIs) in ecology, where one species alters the interchange between two other species. Indeed, the subject of this book has a pervasive relationship with all of ecology, providing a theme and a concept that enmeshes all levels of organization, from individuals to populations, communities, ecosystems and global phenomena. Another term used frequently is ‘strong effect’ for the influence of such indirect interactions in communities and ecosystems. If we are dealing with ever-present and major impacts in ecology, then certainly these kinds of interactions deserve much attention. In fact, the volume of literature in this field appears to be undergoing exponential growth. Therefore, this volume is a timely reminder that the field is expanding rapidly, and a guide on how it can grow along new routes of research and application with time. TMIIs as a category of interchanges in ecology are worthy of attention from all ecologists and those in related fields such as agriculture, forestry, conservation, epidemiology, parasitology and animal husbandry.

We should not be surprised by the pervasive and robust influences of TMIIs. One example: as with humans, all plants and animals produce body odours, but more so than with humans, the body odours in nature have strong effects on other species, both direct and indirect. A phytochemical may have a direct impact on a herbivore, as well as an indirect effect by acting as an attractant to the enemy of the herbivore. In a community of plants, herbivores, parasitoids and predators there is therefore a rich blend of aromas wafting around, mediating the interactions of a multitude of species. These are not necessarily feeding links that would enter into a food web, but they would become important components of an interaction web, far richer than the conventional food web. Similar increases in interaction richness and complexity are observed when we compare direct feeding links on plants versus indirect interactions emanating from herbivores altering plant traits, which provide new resources for other species. Interactions may more than triple in number when trait-mediated interchanges are recognized.