Stouffer, D. B. | bioRxiv Science

bioRxiv2018

pymfinder: a tool for the motif analysis of binary and quantitative complex networks

We developed pymfinder, a new software to analyze multiple aspects of the so-called network motifs--distinct n-node patterns of interaction--for any directed, undirected, unipartite or bipartite network. Unlike existing software for the study of network motifs, pymfinder allows the computation of node- and link-specific motif profiles as well as the analysis of weighted motifs. Beyond the overall characterization of networks, the tools presented in this work therefore allow for the comparison of the \"roles\" of either nodes or links of a network. Examples include the study of the roles of different species and/or their trophic/mutualistic interactions in ecological networks or the roles of specific proteins and/or their activation/inhibition relationships in protein-protein interaction networks. Here, we show how to apply the main tools from pymfinder using a predator-prey interaction network from a marine food web. pymfinder is open source software that can be freely and anonymously downloaded from https://github.com/stoufferlab/pymfinder, distributed under the MIT License (2018).

ecology↗

bioRxiv2018

Uncovering indirect interactions in bipartite ecological networks

Indirect interactions play an essential role in governing population, community and coevolutionary dynamics across a diverse range of ecological communities. Such communities are widely represented as bipartite networks: graphs depicting interactions between two groups of species, such as plants and pollinators or hosts and parasites. For over thirty years, studies have used indices, such as connectance and species degree, to characterise the structure of these networks and the roles of their constituent species. However, compressing a complex network into a single metric necessarily discards large amounts of information about indirect interactions. Given the large literature demonstrating the importance and ubiquity of indirect effects, many studies of network structure are likely missing a substantial piece of the ecological puzzle. Here we use the emerging concept of bipartite motifs to outline a new framework for bipartite networks that incorporates indirect interactions. While this framework is a significant departure from the current way of thinking about networks, we show that this shift is supported by quantitative analyses of simulated and empirical data. We use simulations to show how consideration of indirect interactions can highlight ecologically important differences missed by the current index paradigm. We extend this finding to empirical plant-pollinator communities, showing how two bee species, with similar direct interactions, differ in how specialised their competitors are. These examples underscore the need for a new paradigm for bipartite ecological networks: one incorporating indirect interactions.

ecology↗