Nestedness interacts with subnetwork structures and interconnection patterns to affect community dynamics in ecological multilayer networks

Ecological networks describe ecological interactions among species in ecosystems. In natural ecosystems, plant-mutualist (PM) and plant-herbivore (PH) networks are two of the most documented bipartite ecological networks, which are often interconnected through shared plants to form multilayer networks (here referred to as ecological networks with multiple interaction types). Recent developments in multilayer networks have challenged the effects of topological properties on biodiversity and stability once found in ecological networks with a single interaction type. In this study, my goal was to theoretically test the effects of the nested topology of subnetworks (i.e. plant-mutualist and plant-herbivore networks) on the local stability and persistence of the entire community and determine how their effect sizes were dependent on subnetwork structures and interconnection patterns. I used a simple algorithm to construct plant-mutualist or plant-herbivore networks with different levels of nestedness while fixing connectance and network size. By artificially interconnecting plant-mutualist and plant-herbivore networks through shared plants, I also manipulated the inter-subnetwork connection patterns as positive, negative and no correlations between the number of interacting partners of shared plants of two subnetworks. Community dynamics were simulated to show how subnetwork nestedness interacted with other network properties to affect local stability and persistence of multilayer networks. I found that low nestedness of both plant-mutualist and plant-herbivore subnetworks promoted stability and persistence. Effect sizes of the focal PM- or PH-subnetwork nestedness were positively associated with the nestedness levels of the interconnected subnetworks. A positive correlation between the mutualistic and herbivory generalism of plants also led to higher (signed) effect sizes of subnetwork nestedness. Further analyses showed that the effect sizes of the subnetwork nestedness also depended on subnetwork complexity and intraguild competition intensity. Finally, the modularity of interconnected subnetworks had little association with the effect sizes of subnetwork nestedness irrespective of interconnection patterns. The results demonstrate that the effects of topological structures (such as nestedness) on community dynamics in single-interaction networks may be altered by the architectures of multilayer networks, which highlights the need to study the interactions between the architectures of within- and inter-subnetworks in affecting ecosystem stability and biodiversity.