The movement of a population across an existing physical barrier.
The movement of genes through a population or
between populations through mating.
The offspring of parents of two different species. Hybrids are often unable to
reproduce, whether because of ill health, deformity, or sterility.
A type of reproductive isolation that occurs before the formation of a
zygote can take place. In most cases mating does not even occur. Forms of
prezygotic isolation include spatial, behavioral, mechanical and temporal
A type of reproductive isolation that occurs after members of two different
species have mated and produced a hybrid offspring. Such hybrids are
usually unable to reproduce.
The inability of the individuals of a species to create offspring with
members of any other species. There are two forms: prezygotic and
The division of a population by the appearance of a physical barrier.