The role of different species of snakes in network structure
The correlation between degree and average body mass suggest nestedness was driven by body size. In fact, there is a positive correlation between delta nestedness and average body mass, indicating that the largest snakes have a greater contribution to nestedness (slope = 0.4, R2 = 0.37, p < 0.01, Figure 3). We performed an removal analysis to further explore this pattern. We removed species with more outlier values of average body mass and recalculated the nestedness value. They were the seven largest snake species in the network (Eunectes murinus, Boa constrictor, Lachesis muta, Epicrates cenchria, Corallus hortulanus, Corallus caninus andSpilotes pullatus ). If the largest snakes are key components contributing to nestedness, we expected that nestedness after removal of these species would be smaller than those generated by a null model in which we randomly remove any seven species from the network and recalculate the nestedness. Our results supported this prediction, indicating that the nestedness values ​​were smaller after the removal of the seven largest snake species (N = 30.23, p < 0.01, n = 1,000 simulations of species removal).