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).