File S1 Robustness of the logistic regression approach and of the corrected chi-square test. (1) Conformity tests of the type I error to 5%, (2) Influence of the way to calculate the Pvalue of the corrected chi-square test on the robustness of the study. (DOC) File S2 ''Chi2corr'', an R program for the application of the corrected chi-square test to any presence-absence data: test statistic, observed and expected frequencies, estimated dispersion coefficient (parametric bootstrap), P-values and distribution of the bootstrapped corrected chi-square.