Speciation
Points covered:
- What is speciation?
- What are the three main types of speciation?
- What are examples of the three main types of speciation?
Words to Know:
- SPECIES - a group of organisms which can successfully breed with each other, but have limited success breeding with other groups.
- RANGE - the area in which a species is found.
- ENDEMIC - native to one area or continent only.
Speciation is the evolution of new species. It occurs when a population of interbreeding individuals is split up into separate populations. These separate populations then continue to evolve independently of each other. Over time, they may become separate species and be unable to breed with the populations from which they were initially separated. For animals that reproduce without sex, species are defined by arbitrary decisions based on how genetically distinct groups have become. There are three main types of speciation: range splitting speciation, island-colonisation speciation and non-geographic speciation.
- Range splitting speciation occurs when geographic divisions, such as changes in the environment or landscape, split a species' range. This type of speciation happens over a long period of time. For example, when ocean temperatures around southern Australia cooled during the ice ages, fish species were forced to separate into two groups, as they retreated into warmer waters off the east and west coasts.These two groups then evolved into two different but related species. There are at least 18 examples of such closely related fish species in the east and west of Australia.
- Island colonisation speciation occurs when an area, such as an island, is colonised only once, for instance by a single pregnant female. This type of speciation is more rapid and can be seen in the Drosophila fruit flies in Hawaii. About 750 species of Drosophila are native to the archipelago of Hawaii, and 98% of these are endemic to one island only. Most species groups are derived from a species on another island, meaning that a pregnant female has left one island and colonised another.
- Non-geographic speciation occurs when changes in mating time, behaviour or flowering season prevent individuals of what had been the same species from interbreeding.
Don Colgan
Evolutionary Biology Unit
Australian Museum
