Why are there so many species and interactions in nature? This has been the fundamental question in the field of Biology since the Darwin era. In this context, understanding how biodiversity is created and maintained is one of the most challenging issues in modern ecology. Food webs, based on “who eats whom,” embedded in an ecological community, have long been a basic tool to explore how biodiversity is organized in a wide range of ecosystems.

However, growing evidence is that nontrophic, indirect, and mutualistic interactions, which have not been involved in the traditional food webs, are essential in forming novel interaction networks, thereby enriching biodiversity. It is critical to consider these key interactions because they are ubiquitous and widespread in nature, and they play an important role in determining species and interaction diversity.

My work has focused on the way in which nontrophic, indirect, and mutualistic interactions organize plantbased arthropod communities and alter their biodiversity. In 2005, I proposed a conceptual framework for an “indirect interaction web,” which is an interaction network that enables us to understand the components of species and interaction diversity by focusing on nontrophic, indirect, and mutualistic interactions, as well as trophic interactions. Interaction linkages caused by plant-mediated indirect effects have the potential to greatly enrich biodiversity by increasing the diversity and complexity of the network structure of interacting species. Although feeding relationships are a crucial part of the network structure, food webs provide an incomplete picture of the forces structuring ecological communities and biodiversity because they have ignored the plant-mediated indirect effects induced by herbivores. The indirect interaction web can be utilized to improve our understanding of the complexity of a plant-based ecological community, and this knowledge will aid efforts to conserve interaction biodiversity in nature. Thus, the indirect interaction web has established a novel approach that explicitly incorporates such key interactions into the components of the traditional food webs. This approach can also provide fundamental insights into the big question of how evolution drives the organization of the ecological processes of communities and ecosystems.