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.