The role of snake species in network structure
If the network of interactions analysed follows the organisation pattern
structured by body mass (i.e. presenting higher nestedness than
expected by the null model 2), we hypothesized snake average body mass
to be positively correlated with the number of resources consumed by the
snake species. To explore this prediction, we investigate the
association between average body mass and the role of species in the
network structure. We recorded the estimates of the average body mass of
each snake species in our network (data available in Feldman et al.
2016). Average body mass was log-transformed prior to analysis
(Supplementary material Appendix 2 Table A1).
In order to understand the individual contribution of each species of
snake to nestedness, we used a jackknife resampling approach in which we
removed a snake species and recomputing the degree of nestedness. We
repeated the procedure for all snake species in the network and then we
computed a change in nestedness: ΔNi = N -
Ni, in which N is the degree of nestedness of
the complete network and Ni is the degree of
nestedness after the removal of a snake species i . If body size
is shaping the contribution to nestedness, we should expect that theΔNi will assume increasingly positive values as
larger snakes are removed from the network, indicating that nestedness
is higher in the presence of these larger snake species.