A framework for hierarchical compound topologies in species interaction networks

Abstract

Hierarchical compound topologies of interaction networks that are segmented into internally nested modules have received scant attention, compared to simple nested and modular topologies. This is due to the lack of a theoretical model that encompasses all relevant alternative topologies, and an effective method to differentiate compound from simple topologies. Here we present a framework to address compound topologies in ecological networks. We propose a mechanistic schema of processes that generate modular, nested and compound topologies, based on differences in availability and preferences among species. We show that, in combination, these processes produce a unique signature in the structure of compound topologies. Then, we propose a procedure to identify this signature and hence discriminate among simple and compound topologies. We test the efficiency of this procedure in a set of synthetic matrices and then apply it to an actual plant–herbivore network (Asteraceae and their flowehead feeders in Brazil). In this case, the compound topology is clearly substantiated, demonstrating that these advances are applicable to empirical ecological networks and that compound patterns decidedly belong to the array of topologies to be probed in interaction assemblages at various scales. By including extramodular structures in the analysis of compound topologies, we enhance our understanding of how community‐wide networks are organized and their responses to various drivers.

Composition, structure and robustness of Lichen guilds

“…Nestedness and modularity are not exclusive to particular interaction types 73 , and they can also coexist, occupying different scales in the ecological network (e.g. modules that are themselves nested 46 , 74 , 75 ) or different dimensions of hypergraph ecologies 76 . Our results suggest the presence of non-mutualistic interactions among lichen symbionts, whether antagonism or facultative mutualism 42 , 68 , 69 .…”

Composition, structure and robustness of Lichen guilds

“…Nestedness and modularity are not exclusive to particular interaction types 68 , and they can also coexist, occupying different scales in the ecological network (e.g. modules that are themselves nested 39,69,70 ) or different dimensions of hypergraph ecologies 71 . Our results suggest the presence of non-mutualistic interactions among lichen symbionts, whether antagonism or facultative mutualism 43,63,64 .…”