Prezygotic barriers
habitat isolationThis occurs when two species live in the same geographic area but in different habitats. As a result, they will not interact with each other and speciation will take place.
In the picture above are two garter snakes that are very different because of their different habitats. |
Mechanical isolationWhen two species have different physical or biological so that fertilization cannot occur. It is more often than not a difference in the size or fit of genitalia of the two species.
For example, the snails have shells spiraling in the opposite direction so that the two snails cannot mate. |
Temporal IsolationTemporal isolation signifies that because those species mate during different times, mating is prevented. It may range from different times of the day, different seasons, or even different years. |
Behavioral IsolationBehavioral isolation refers to the different signals or types of behavior to attract the opposite sex, but of the same species.
If the incorrect signal or behavior is displayed, the potential mate does not respond and mating does not occur. The two pairs of birds above look extremely similar but are in fact different species. They identify mates of the same species is by looking for birds that partake in the courting dance, or in the pointing display. |
GAmetic IsolationGametic isolation is when the gametes of two different species meet, but something physical or chemical prevents a zygote from forming. Typically, it is because either the sperm cannot survive in the female's reproductive tract or because the sperm cannot penetrate the egg.
Sea urchins shed their gametes into the ocean water where the sperm and egg can then fuse into a zygote. But the gametes of two different species cannot fuse because the surface proteins of the ovule and sperm do not fit together. Thus, a hybrid gamete is not formed. |