There is a growing body of evidence suggesting that locally rare and g
eographically restricted species may have characteristics that differ
from those of taxa that are more common. Several studies show that rar
e taxa have lower levels of self-incompatibility, a tendency toward as
exual reproductive pathways, lower overall reproductive effort and poo
rer dispersal abilities. There are several mechanisms that could be re
sponsible for such differences, but they may in practice be difficult
to differentiate. Nonetheless, the documentation of recurrent rare-com
mon differences is of vital importance because it may allow us to comp
ensate partially for the bias of the published literature toward studi
es of common taxa.