n_w

Net_Work

Trophic Networks Analysis

Version 2.0 - May 2017

The n_w computer program is designed for the study of the structure and functionnalities of trophic networks (food webs), and more generally systems represented by a directed graph. It is convivial and easy to use.

The n_w program is distributed free of charge. Users are under their own responsibility.

 After installation, the n_w directory should contain:

• The n_w program executable file nw.exe
• Text files *.nw0, *.nw1, *.nw2, *.gml describing example networks
• The reference manual nwref.pdf

How to run the n_w program?

• Double-click on any file *.nw0. Select program nw.exe to open the file
• The n_w program will then create the network described by the file and compute its descriptors
• Several commands allow to study the network
• For detailed informations consult nwref.pdf

What is a food web?

A food web is a set of species related by trophic interactions (who eats whom) within an ecosystem. A food web comprising S species can be represented by a directed graph or network whose nodes are the species and whose arcs describe the feeding links. In the network representing the food web, there is an arrow joining each prey (resource) species to its predator (consumer) species.
A food web can be represented by a (0,1)-matrix A = (a_ij) of size S, where a_ij = 1/0 depending of the presence/absence of a feeding link between species i and species j. A matrix W = (w_ij) ascribing non negative weights w_ij to trophic links can also be introduced (A and W have the same non zero entries). The matrix of weights represents biological values associated with trophic interactions, like energy flux, probability of capture, consumption rate.

What is provided by the n_w program?

With the n_w program, several food webs can be studied simultaneously, observed ones, which are specified in text files, or synthetic (random) ones, which are created using predefined models. The studied networks can be edited and displayed graphically. Results are stored in text and graphic files.

Analysis of structural and functional properties of empirical and synthetic trophic networks:

• Topological descriptors --> structural properties of the network
• Graphical representation according to trophic height, trophic level
• Network editing facilities
• Network generation
• Network partition into modules, trophic groups --> functional properties of the network
• Aggregation into simplified networks --> functional properties of the network

References

Authors

Mail to Stéphane Legendre

Contribution

Jacques Gignoux, Gérard Lacroix, Xavier Lazzaro, Elisa Thébault.