Shifting levels of ecological network's analysis reveals different system properties

Abstract

Network analyses applied to models of complex systems generally contain at least three levels of analyses. Whole-network metrics summarize general organizational features (properties or relationships) of the entire network, while node-level metrics summarize similar organization features but consider individual nodes. The network- and node-level metrics build upon the primary pairwise relationships in the model. As with many analyses, sometimes there are interesting differences at one level that disappear in the summary at another level of analysis. We illustrate this phenomenon with ecosystem network models, where nodes are trophic compartments and pairwise relationships are flows of organic carbon, such as when a predator eats a prey. For this demonstration, we analysed a time-series of 16 models of a lake planktonic food web that describes carbon exchanges within an autumn cyanobacteria bloom and compared the ecological conclusions drawn from the three levels of analysis based on inter-time-step comparisons. A general pattern in our analyses was that the closer the levels are in hierarchy (node versus network, or flow versus node level), the more they tend to align in their conclusions. Our analyses suggest that selecting the appropriate level of analysis, and above all regularly using multiple levels, may be a critical analytical decision. This article is part of the theme issue ‘Unifying the essential concepts of biological networks: biological insights and philosophical foundations'.

Strong reorganization of multi-domain microbial networks associated with primary producers sedimentation from oxic to anoxic conditions in an hypersaline lake

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“…number of nodes or links, diameter, centralized metrics) and there are few studies that dare to dive into the complexity of the graph objects to provide deeper analyses of their structure. Indeed, networks are organized into different structural levels (network, modules, nodes and links) that complement each other and could provide deeper insights about the studied system if considered simultaneously (Niquil et al 2020). Nodes identity and associations with each other provide information on their putative interactions, modules are groups of taxa closely associated that could correspond to functional groups with similar or complementary capabilities, and global network characteristic represent the system as a whole (Karimi et al 2017;Pellissier et al 2018;Delmas et al 2019).…”

Methodological overview and data‐merging approaches in the study of plant–frugivore interactions

“…the effect magnitude of its outcome, in addition to its frequency of occurrence) can change depending on the focus of study and how its outcome for the partners is measured. Therefore, the study question will determine when and how interactions are monitored (Niquil et al 2020).…”

Unifying the essential concepts of biological networks: biological insights and philosophical foundations

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