The Kulczynski distance between two species is 1-(mean of (number of
regions where
both species are present)/(number of regions where species 1 is
present) and (number of
regions where
both species are present)/(number of regions where species 2 is
present)). The similarity version of this is S28 in Shi (1993).
References
Shi, G. R. (1993) Multivariate data analysis in palaeoecology and
palaeobiogeography - a review. Palaeogeography,
Palaeoclimatology, Palaeoecology 105, 199-234.