Seeing the forest for the trees: Putting multilayer networks to work for community ecology

Abstract

A framework for the description and analysis of multilayer networks is established in statistical physics, and calls are increasing for their adoption by community ecologists. Multilayer networks in community ecology will allow space, time and multiple interaction types to be incorporated into species interaction networks. While the multilayer network framework is applicable to ecological questions, it is one thing to be able to describe ecological communities as multilayer networks and another for multilayer networks to actually prove useful for answering ecological questions. Importantly, documenting multilayer network structure requires substantially greater empirical investment than standard ecological networks. In response, we argue that this additional effort is worthwhile and describe a series of research lines where we expect multilayer networks will generate the greatest impact. Inter‐layer edges are the key component that differentiate multilayer networks from standard ecological networks. Inter‐layer edges join different networks—termed layers—together and represent ecological processes central to the species interactions studied (e.g., inter‐layer edges representing movement for networks separated in space). Inter‐layer edges may take a variety of forms, be species‐ or network‐specific, and be measured with a large suite of empirical techniques. Additionally, the sheer size of ecological multilayer networks also requires some changes to empirical data collection around interaction quantification, collaborative efforts and collation in public databases. Network ecology has already touched on a wide swath of ecology and evolutionary biology. Because network stability and patterns of species linkage are the most developed areas of network ecology, they are a natural starting place for multilayer investigations. However, multilayer networks will also provide novel insights to niche partitioning, the connection between traits and species’ interactions, and even the geographic mosaic of co‐evolution. Synthesis. Multilayer networks provide a formal way to bring together the study of species interaction networks and the processes that influence them. However, describing inter‐layer edges and the increasing amounts of data required represent challenges. The pay‐off for added investment will be ecological networks that describe the composition and capture the dynamics of ecological communities more completely and, consequently, have greater power for understanding the patterns and processes that underpin diversity in ecological communities. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13237/suppinfo is available for this article.

Agricultural intensification drives changes in hybrid network robustness by modifying network structure

“…These "single-type" sub-networks are valuable but they belie the multitude of complex interactions shaping species' abundance, fitness and persistence (Pocock et al 2012;Garc ıa-Callejas et al 2018). Therefore, there has been a recent emphasis on networks that contain multiple interaction types (Meli an et al 2009;Fontaine et al 2011;Mougi & Kondoh 2012D attilo et al 2016;Sauve et al 2016;Lurgi et al 2016;Astegiano et al 2017;Pilosof et al 2017;Ramirez et al 2018;Garc ıa-Callejas et al 2018;Delmas et al 2019;Hutchinson et al 2019). We specifically use the term "hybrid" here to mean networks that combine two or more types of interactions, like antagonisms (À/+) and mutualisms (+/+) (as in Mougi & Kondoh 2014;Suweis et al 2014).…”

Identifying flow modules in ecological networks using Infomap

“…Modelling coupling without provided interlayer links is particularly useful in ecology because interlayer links are often challenging to measure empirically (Hutchinson et al, 2018). If interlayer links are not provided, a random walker moves within a layer and, with a given 'relax rate' r, jumps to the current physical node in a random layer without recording this movement, such that the constraint to move only within layers can be gradually relaxed ( Fig.…”

Interaction networks and trait evolution

“…In a natural population, a given plant interacts with pollinators but also with herbivores, predators, plants species, microorganisms and other organisms. This leads to multilayered species interactions that are structured in species ecological networks (Hutchinson et al , 2019). Pedro Jordano (Estación Biológica de Doñana, Seville, Spain), in a study on the tree Prunus mahaleb , explored the biological meaning of the connections among different layers: pollinators, seed disperser, and herbivores.…”