Importance of demography in understanding disease ecology in small mammals

Small rodents are increasingly used as model animals in disease ecological research.  However, many students in the field have an inadequate knowledge of the significance of demographic heterogeneity of reservoir rodent populations and how that affects infection parameters.  I summarize here some of the common problems and give a solution, the use of the concept of functional groups, to gain more detailed information and avoid common mistakes (e. g., by drawing conclusion from pooled population samples).  I emphasize the importance of seasonality and demography (roles of various population functional subgroups) for parasite/pathogen studies and sampling design to cover the essential components of populations.