Nestedness is a measure of structure in an ecological system, usually applied to species-sites systems (describing the distribution of species across locations), or species-species interaction networks (describing the interactions between species, usually as bipartite networks such as hosts-parasites, plants-pollinators, etc.).
[2][3] A software (BINMATNEST) is available from the authors on request and from the Journal of Biogeography to correct these deficits [4] In addition, ANINHADO solves problems of large matrix size and processing of a large number of randomized matrices; in addition it implements several null models to estimate the significance of nestedness.
[5][6] Bastolla et al. introduced a simple measure of nestedness based on the number of common neighbours for each pair of nodes.
For instance, two insect species might "help" each other by pollinating the same subset of plants, thereby reducing the extent to which they are harmful to each other.
[8] These authors propose a refined version of the measure, and go on to show how certain network properties affect nestedness.