The relationship between lifestyles and network structure
Because dietary specialisation in snakes can be related to habitat
occupation (see Martins et al. 2002, Alencar et al. 2017), we expect
snake lifestyles to affect the degree of dietary specialisation (e.g.,
an aquatic snake would rely upon aquatic prey). If this is true, the
distribution of lifestyles in the different modules will not be random.
We evaluated this prediction using two analyses. First, we analysed the
frequency of snake lifestyles in different modules. We estimated the
probability of the observed number of species of a given lifestyle in a
given module be reproduced by randomly assigning species across modules,
but preserving the number of snake species in each lifestyle and the
number of snake species in each module (n = 1000 randomisations). Then,
we analysed the dissimilarity on lifestyles between modules. To do so,
we used the Bray-Curtis index, available in vegan package in R (Oksanen
et al. 2018) (see detailed description in Supplementary material
Appendix 1). Dissimilarity between a pair of modules range from 0
(modules are identical in the composition of lifestyles) to 1 (no
lifestyle occurs in both modules).