Nested interaction networks represent a missing link in the study of behavioural and community ecology

Abstract

Interactions are ubiquitous across biological systems. These interactions can be abstracted as patterns of connections among distinct units such as genes, proteins, individual organisms, or species which form a hierarchy of biological organisation. Connections in this hierarchy are arranged in a nested structure: gene and protein networks shape phenotypic traits and together constitute individuals, individuals are embedded within populations, populations within communities, and communities within ecosystems. This pervasive "nestedness" of networks can result in propagation of the effects from within-level interactions at one level to units at higher or lower levels of organization. The concept of nested biological networks is implicit in a variety of disciplines ranging from the study of genetic circuits regulating phenotypic trait expression (Babu et al. 2004), to the study of predator-prey interactions influencing community composition (Poisot et al. 2016). However, studies typically only address interactions within and among directly neighbouring hierarchical levels, such as genotypes and phenotypic traits, or populations and communities. Here, we formalise nested networks as having nodes that can contain, or be embedded in, other nodes, and where edges can bridge connections between sets of embedded nodes. We then argue that explicitly accounting for network nestedness across levels of organization will encourage integrative thinking on new interdisciplinary research fronts. We focus on two phenomena in particular: (i) indirect connections among units can arise from the structure of connections at higher or lower levels of organisation, (ii) the propagation of effects across neighbouring hierarchical levels of organization. This framework of nested interaction networks provides a tool for researchers across disciplines to conceptualize their work as elements on a common scaffold.