Sensitivity analyses
Sampling effects may affect the description of network patterns.
Therefore, we performed a sensitivity analysis to explore how robust is
the description of network patterns to changes in our dataset. We add
information to the use of resources by snakes by using data from other
Amazonian regions, based on evidence that there is no significant
intraspecific variation on the snake’s diet across different localities
in Amazonia (Martins and Oliveira, 1998; Supplementary material Appendix
1 and Appendix 2 Table A1).
Snake diet often include food resources that are main consumed and
resources that are only eventually consumed. We performed a sensitivity
analysis to check if the patterns reported in our study are robust
enough when considering the presence or absence of secondary resources
in the snake diet. We described two matrices of interactions: (1) a
matrix in which only main resources were considered; (2) and a matrix in
which both main and secondary resources were considered. We defined if a
resource is main or secondary according to information about snake diet
preferences available in Martins and Oliveira (1998). Then, we calculate
the nestedness and modularity values in the presence and absence of
secondary resources. The nestedness values of the two networks were
compared with a null model generated with 5,000 random removals of food
resources from each of the analysed networks. Finally, we calculated
whether there was a significant difference between the nestedness of the
network in the presence and absence of secondary resources.
Because taxonomic resolution might influence the detection of patterns
in the network (Rezende et al. 2009), we performed another sensitivity
analysis to check if the type of resource categorization could affect
the network patterns. Thus, we described two other matrices of
interaction with different degrees in the resources taxonomic
resolution: less specific network (Supplementary material Appendix 1
Figure A2 and Appendix 3 Table A1) and more specific network
(Supplementary material Appendix 1 Figure A3 and Appendix 4 Table A1).