COS 152-3 - Traits constrain species roles in multiplex ecological networks

Abstract: Ecosystems are composed of many species, interacting in diverse ways. Ecological networks describe the structure of species interactions (“who interacts with whom”) within an ecosystem. Research on these networks has traditionally been restricted to subsets of the species or interactions in ecosystems, such as pollination networks or food webs. This restriction is often due to the assumption of different underlying assembly mechanisms for “subnetworks” of different interaction types, such as different ecological traits and sets of “interaction rules” that determine an interaction between two species. As a result, the structure of “multiplex” networks that include multiple interaction types is still unknown. Ecological traits, including those that determine different interactions like body size or length of mouth parts, are often strongly related to each other due to evolutionary history, allometry, and diffuse selection. Such trait correlations are thought to constrain species roles in ecosystems and thus may constrain the structure of ecological networks. Here, we leverage this idea in a model that simulates multiplex ecological networks by interconnecting subnetworks using correlated traits. We show that multiplex network structure (measured as the overlaps between species’ functional roles) is affected by neutral processes, interaction rules, and trait constraints, but that the structure of individual subnetworks is independent of these trait constraints. Additionally, multiplex structure can be predicted from simple expectation functions using only subsets of the species and types of interactions in the network. This suggests that subnetwork structure is independent of potential trait constraints imposed by other interaction types and that properties of interconnection in natural ecosystems may be assessed from the interconnections in available data. Our model provides a structural backbone for future studies of multiplex dynamics and function and a null model to investigate ecosystem assembly under multiple trait constraints.