In behavioral isolation, patterns of courtship may be altered to the extent that sexual union is not achieved.
In temporal isolation, different groups may not be reproductively mature at the same season, or month, or year.
In mechanical isolation, two populations are mechanically isolated when differences in reproductive organs prevent successful interbreeding.
In ecological isolation, potential mates may be in the same general area but not in the same habitat where they are likely to meet.
In gametic mortality, incompatibilities between egg and sperm prevent fertilization.