NOS {bipartite}

Calculates the node overlap and separation according to Strona & Veech (2015)

Description

This index computes a variation of nestedness, called node overlap and segragation, as well as a modularity measure

Usage

NOS(web, keep.Nij=FALSE, keep.diag=FALSE)

Arguments

web

A bipartite interaction web, i.e.~a matrix with higher (cols) and lower (rows) trophic levels.

keep.Nij

Shall node overlap matrix for each trophic level be returned, too? Logical, defaults to FALSE.

keep.diag

Shall the diagonal of Nij be kept at a value of 1, or rather be omitted from computations? If the diagnoal is kept, the index will not be centred on zero as described in the paper. However, the paper is unclear about this point, and hence the option to keep the diagonal (rather than setting omitting it from computation) is offered. Logical, defaults to FALSE.

Details

According to the authors, NOS is “a new statistical procedure to measure both [the tendency of network nodes to share interaction partners] and the opposite one (i.e. species’ tendency against sharing interacting partners) that we call ‘node segregation’. In addition, our procedure provides also a straightforwardmeasure of modularity, that is, the tendency of a network to be compartmented into separated clusters of interacting nodes.”

Value

Nbar

the NOS-value (referred to by the authors as a funny N (which with the fc-package in LaTeX is coded as ⁠\m{J}⁠, apparently).

mod

modularity, computed as mean standard deviation of the Nij-values for each trophic level.

Nbar_higher

the NOS-value for the higher trophic level.

Nbar_lower

the NOS-value for the lower trophic level.

mod_higher

the mod-value for the higher trophic level.

mod_lower

the mod-value for the lower trophic level.

N_ij_higher

Optional; the matrix of NOS-values for each species pair, for the higher trophic level.

N_ij_lower

Optional; the matrix of NOS-values for each species pair, for the lower trophic level.

Author(s)

Carsten F. Dormann [e-mail], with additional code provided by “tchen98” (on github).

References

Strona, G., and Veech, J.A. (2015) A new measure of ecological network structure based on node overlap and segregation. Methods in Ecology & Evolution 15, 319–328

See Also

grouplevel, which eventually shall use this function.

Examples

data(Safariland)
# illustrate difference between keeping/removing the diagonal:
NOS(Safariland)
NOS(Safariland, keep.diag=TRUE)