Abstract
Investigating the structure of ecological networks can help unravel the mechanisms promoting and maintaining biodiversity. Recently, Strona and Veech 2015 (A new measure of ecological network structure based on node overlap and segregation. – Methods Ecol. Evol. 6: 907–915) introduced a new metric (Ɲ̅, pronounced ‘nos’), that allows assessment of structural patterns in networks ranging from complete node segregation to perfect nestedness, and that also provides a visual and quantitative assessment of the degree of network modularity. The Ɲ̅ metric permits testing of a wide range of hypotheses regarding the tendency for species to share interacting partners by taking into account ecologically plausible species interactions based on constraints such as trophic levels and habitat preference. Here we introduce NOS, a software suite (including a web interface freely accessible at http://nos.alwaysdata.net , an executable program, and Python and R packages) that makes it possible to exploit the full potential of this method. Besides computing node overlap and segregation (Ɲ̅), the software provides different functions to automatically identify a set of possible resource–consumer interactions in food webs based on trophic levels. As an example of application, we analyzed two well‐resolved high‐latitude marine food webs, showing that an explicit a priori consideration of trophic levels is fundamental for a proper assessment of food web structure.
Highlights
Natural systems are bound together by invisible wires connecting ecologically interacting species. These can be arranged into bipartite networks, i.e. networks where interactions can take place only between the members of two distinguishable groups, or into unimode networks, where such distinction is not straightforward
Similar to these other nestedness metrics, Ɲcan be applied to species/locality matrices, because these correspond to bipartite networks where localities are linked to the species inhabiting them
Analyzing the distribution of Ɲij values provides an immediate visual way to distinguish between random and modular networks, with the latter showing a bimodal distribution of Ɲij values, with a negative peak arising from node segregation between different modules, and a positive one arising from node overlap within modules
Summary
NOS: A software suite to compute node overlap and segregation ( ) in ecological networks Document Version Publisher's PDF, also known as Version of record Citation for published version (Harvard): Strona, G, Matthews, T, Kortsch, S & Veetch, JA 2018, 'NOS: A software suite to compute node overlap and segregation ( ) in ecological networks', Ecography, vol 41, no. 3, pp. 558–566. https://doi.org/10.1111/ecog.03447
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