Describe and explain the different types of speciation.

What is Speciation? This is the formation of a new species. a species is a group of organisms that can interbreed to produce fertile offspring. Members of a species belong to the same gene pool.

What is Speciation? For a new species to form there must be separation of the gene pool of the species from the gene pool of the parent population. This means that the splinter group can follow its own evolutionary path.

The first steps of speciation have been produced in several laboratory experiments involving “geographic” isolation. Diane Dodd took fruit flies from a single population and divided them into separate populations living in different cages to simulate geographic isolation. Half lived on maltose-based food, and the other on starch-based foods. After many generations, the flies were tested to see which flies they preferred to mate with. Dodd found that some reproductive isolation had occurred as a result of the geographic isolation and selection in the different environments:

Types of Speciation. There are two types of speciation, based on the geographical relationship of the new population to its ancestral species. Allopatric Speciation Sympatric Speciation.

Allopatric Speciation This is when a species population is separated by a geographical barrier. The species are known as allopatric populations. Greek: allos means other. Latin: patria means homeland

Allopatric Speciation

Allopatric Speciation

How Allopatric Speciation Occurs. Reduced Selection Pressure a population moves into a new area free from competing species, predators, etc, with many niches unfilled. A population explosion follows this results in increased variation as most offspring survive, so alleles that were previously selected against are now expressed.

How Allopatric Speciation Occurs. Migration into new environments on the borders of the range give rise to sub-species with different natural selection pressures. Geographical barriers arise between sub-species, giving rise to geographical isolation.

How Allopatric Speciation Occurs. The isolated populations will experience different mutations that will not flow to the parent population. Isolated populations will usually be exposed to different environmental selection pressures as they occupy different ranges.

How Allopatric Speciation Occurs. Some of the isolated sub-species develop genetic and chromosomal differences that will no longer allow interbreeding with the parent population. They are now genetically isolated and, thus, a new species.

Sympatric Speciation This occurs when a sub-population becomes reproductively isolated in the midst of the parent population. Populations are said to be sympatric if their ranges overlap. These are species of the same genus living together in the same area. Greek: sym means together

Sympatric Speciation Gene flow has been reduced between flies that feed on different food varieties, even though they both live in the same geographic area.

Speciation.