• Additive model;
  • Case-control study;
  • Direct gradient analysis;
  • Gaussian logit curve;
  • Generalized linear model (GLM);
  • Logistic regression;
  • Plant species distribution;
  • Plant species-climate relationship;
  • Response curve;
  • Smoother

Abstract. Generalized additive models (GAMs) are a non-parametric extension of generalized linear models (GLMs). They are introduced here as an exploratory tool in the analysis of species distributions with respect to climate. An important result is that the long-debated question of whether a response curve, in one dimension, is actually symmetric and bell-shaped or not, can be tested using GAMs. GAMs and GLMs are discussed and are illustrated by three examples using binary data. A grey-scale plot of one of the fits is constructed to indicate which areas on a map seem climatically suitable for that species. This is useful for species introductions. Further applications are mentioned.