The importance of being random! Taking full account of random effects in nonlinear sigmoid hierarchical Bayesian models reveals the relationship between deadwood and the species richness of saproxylic beetles

•More complex sigmoid functions can improve biodiversity-environment models.•Spatial random effects should not be automatically applied only on the intercept.•Different assessment criteria are complementary to analyze statistical models.•Relationship between saproxylic beetles and deadwood volume varied among forests.