Does biogeography need species?

The non–equivalence of species defined using different species concepts has recently been highlighted as a serious impediment for conservation efforts. The question arises then, to what extent biogeographical studies, and especially macroecological studies, might also be hampered by the numerous problems pertaining to multi–species datasets. An examination of what is meant by species across spatial scales reveals an important discontinuity. Over and above the much–debated species concepts the word ‘species’ describes, in fact, two distinct ideas. One, applicable at the local scale, is critical in a community ecology context. The second refers to non–equivalent units in the global inventory of biodiversity, useful for reference purpose, but problematic where analysis is concerned. The majority of biogeographical studies are in fact relevant to those intermediate spatial scales where neither meaning truly applies. Multi–species lineages that are comparable in one or another respect (such as equal–age lineages and similar–range lineages) are probably more accurate units for testing biogeographical hypotheses