text: Comparative biogeography The study of comparative biogeography can follow two main lines of investigation:
  Systematic biogeography, the study of biotic area relationships, their distribution, and hierarchical classification
  Evolutionary biogeography, the proposal of evolutionary mechanisms responsible for organismal distributions. Possible mechanisms include widespread taxa disrupted by continental break-up or individual episodes of long-distance movement.
  Biogeographic regionalisations
  There are many types of biogeographic units used in biogeographic regionalisation schemes, as there are many criteria (species composition, physiognomy, ecological aspects) and hierarchization schemes: biogeographic realms (ecozones), bioregions (sensu stricto), ecoregions, zoogeographical regions, floristic regions, vegetation types, biomes, etc.
  The terms biogeographic unit, biogeographic area  can be used for these categories, regardless of rank.
  In 2008, an International Code of Area Nomenclature was proposed for biogeography. It achieved limited success; some studies commented favorably on it, but others were much more critical, and it "has not yet gained a significant following". Similarly, a set of rules for paleobiogeography has achieved limited success. In 2000, Westermann suggested that the difficulties in getting formal nomenclatural rules established in this field might be related to "the curious fact that neither paleo- nor neobiogeographers are organized in any formal groupings or societies, nationally (so far as I know) or internationally — an exception among active disciplines."