Analysis of bipartite ecological networks

Version 1.0 - May 2015

The a2b computer program is designed to study bipartite ecological networks. Its merits are:

a2b program download

The a2b program is distributed free of charge. Users are under their own responsibility.

Computer / System



PC Windows

Self-extracting file

Double-click on autoa2b.exe

It will expand in a user chosen directory 

 After installation, the a2b directory should contain:

How to run the a2b program?

What is a bipartite ecological network?

In a bipartite network, 2 sets of nodes, here called A-species and B-species, are joined by interaction links. For example, in a plant-pollinator network, pollinators are the A-species, plants are the B-species, and links represent mutualistic interactions between plants and pollinators (feeding of pollinators on plants, plant gametes dispersal by pollinators). Other examples of bipartite ecological networks are host-parasite antagonistic networks, site-species biogeographical networks, plant-seed disperser mutualistic networks, male-female mating networks.
A bipartite network comprising A-species in number A and B-species in number B, is represented by a (0,1)-matrix M = (mab) that is rectangular of size AxB. The entry mab = 1/0 of the matrix M indicates the presence/absence of an interaction link between the A-species a and the B-species b. A matrix W = (wab) ascribing nonnegative weights wab to interaction links can also be introduced (A and W have the same nonzero entries). The matrix of weights represents biological values associated with  interactions, e.g., number of visits of plants by pollinators.

What is provided by the a2b program?

With the a2b program, several bipartite networks can be studied simultaneously, empirical ones, specified in text files, or synthetic (random) ones, created using predefined models. The networks can be edited and displayed graphically. Results are stored in text and graphic files.

Network descriptors proposed by a2b program allow to analyze patterns and functionalities of a given ecological network via its topological properties, in particular

These 3 notions are crucial for the functionality of the network. They are related in non obvious ways.

Modularity - Clements & Long 1923

Decomposition of the Clements&Long_1923plant-pollinator network (A = 275 pollinator species, B = 96 plant species, L = 923 interaction links) into modules, represented by diagonal blocs in the (0,1)-matrix of the network.

Rustness - Clements & Long 1923

Robustness curves (tolerance to random extinction of pollinator species) for the Clements&Long_1923 plant-pollinator network. 
Proportion of deleted pollinator species  in abscissa versus proportion of
remaining plant species in ordinates. (1) Lower curve, deletion according to decreasing number of links. (2) Middle curve, random deletion. (3) Upper curve, deletion according to increasing number of links.


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Stéphane Legendre
Ecole Normale Supérieure
46 rue d'Ulm
75230 Paris Cedex 05

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Elisa Thébault, Colin Fontaine.