• 1 Modélisation mathématique et informatique de systèmes complexes naturels, biologiques ou sociaux
• 2 Institut Rhône-Alpin des systèmes complexes

Models in population dynamics can deal with an important number of parameters and variables, which can make them difficult to analyse. Aggregation of variables allow reducing complexity of such models by building simplified models governing fewer variables by use of the existence of different time scales associated to the processes governing the whole system. Those reduced models allows analysing and describing the global dynamics of the system. We present those methods for time discrete models and illustrate their use for the study of spatial host-parasitoids models.