Calculates a specialisation index based on the node positions for all species in a bipartite network, separately for the higher and lower trophic level.
nodespec(web, inf.replace = NA)A list with two components, names “higher” and “lower”, both containing the node specialisation index for each species.
A matrix with lower trophic level species as rows, higher trophic level species as columns and number of interactions as entries.
What should infinite geodesic distances (e.g. between compartments) be represented as? Defaults to NA; only currently implemented alternative is inf.replace=Inf, which replaces infinite distances by the maximum path length plus 1.
Carsten F. Dormann carsten.dormann@biom.uni-freiburg.de
This index aims to describe the functional specialisation of pollinators and was proposed by Dalgaard et al. (2008). It is a purely qualitative measure.
After calculating the geodesic distances between species, i.e. the minimum number of steps from one species to another, these values are averaged for each species. This mean geodesic distance is interpreted as functional specialisation (Dalgaard et al. 2008).
Notice that this ``new'' index is in fact little else than the inverse of (unscaled) closeness centrality in disguise.
Dalsgaard, B., Martín González, A. M., Olesen, J. M., Timmermann, A., Andersen, L. H. and Ollerton, J. (2008) Pollination networks and functional specialization: a test using Lesser Antillean plant-hummingbird assemblages. Oikos 117, 789--793
See also as specieslevel, which calls nodespec.
data(Safariland)
nodespec(Safariland, inf.replace=Inf)
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