Computes end-point degrees for a bipartite network, following the suggestion of Barrat et al. (2004)
endpoint(web)A matrix of end-point degrees
A matrix with pollinators as columns and plants as rows. Alternatively, when used on e.g. species occurrences across islands, rows are islands.
Carsten F. Dormann
Computation follows the outline of Gitarranz et al. (2004): ``the product k_i k_j of the degree of the two nodes connected by that link''. We then set additionally endpoint degrees for all non-existing links to 0! Thus, only for existing links endpoint degrees are computed. This is (to me) not obvious from the description in Gitarranz et al. (2004).
Barrat, A., M. Barthélemy, R. Pastor-Satorras, and A. Vespignani. 2004. The architecture of complex weighted networks. Proceedings of the National Academy of Sciences of the USA 101, 3747-–3752. doi: 10.1073/pnas.0400087101.
Gilarranz, L. J., J. M. Pastor, and J. Galeano. 2011. The architecture of weighted mutualistic networks. Oikos 121, 1154–-1162. doi: 10.1111/j.1600-0706.2011.19592.x.
# reproduces the example of Gitarranz et al. (2011):
data(memmott1999)
ends <- endpoint(memmott1999)
weights.mean <- tapply(memmott1999, ends, mean)
ends.weights <- tapply(ends, ends, mean)
plot(weights.mean, ends.weights, log="xy", pch=16)
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