Changes

===Speciation===

===Speciation===

[[Speciation]] is the process where a species diverges into two or more descendant species.<ref name=Gavrilets>{{cite journal |author=Gavrilets S |title=Perspective: models of speciation: what have we learned in 40 years? |journal=Evolution |volume=57 |issue=10 |pages=2197–215 |year=2003 |pmid=14628909}}</ref> It has been observed multiple times under both controlled laboratory conditions and in nature.<ref>{{cite journal |author=Jiggins CD, Bridle JR |title=Speciation in the apple maggot fly: a blend of vintages? |journal=Trends Ecol. Evol. (Amst.) |volume=19 |issue=3 |pages=111–4 |year=2004 |pmid=16701238}}<br />*{{cite web|author=Boxhorn, J|date=1995|url=http://www.talkorigins.org/faqs/faq-speciation.html|title=Observed Instances of Speciation|publisher=The TalkOrigins Archive|accessdate=2007-05-10}}<br />*{{cite journal |author=Weinberg JR, Starczak VR, Jorg, D |title=Evidence for Rapid Speciation Following a Founder Event in the Laboratory |journal=Evolution |volume=46 |issue=4 |pages=1214–20 |year=1992 |doi=10.2307/2409766}}</ref> In sexually-reproducing organisms, speciation results from reproductive isolation followed by genealogical divergence. There are four mechanisms for speciation. The most common in animals is [[allopatric speciation]], which occurs in populations initially isolated geographically, such as by [[habitat fragmentation]] or migration. As selection and drift act independently in isolated populations, separation will eventually produce organisms that cannot interbreed.<ref>{{cite journal|author=Hoskin CJ, Higgle M, McDonald KR, Moritz C |date=2005 |title=Reinforcement drives rapid allopatric speciation |journal=Nature |volume=437 |pages =1353–356|doi=10.1038/nature04004}}</ref>

[[Speciation]] is the process where a species diverges into two or more descendant species. (Perspective: models of speciation: what have we learned in 40 years? journal=Evolution |volume=57 |issue=10 ) It has been observed multiple times under both controlled laboratory conditions and in nature.(Jiggins CD, Bridle JR |title=Speciation in the apple maggot fly: a blend of vintages?) [http://www.talkorigins.org/faqs/faq-speciation.html]| In sexually-reproducing organisms, speciation results from reproductive isolation followed by genealogical divergence. There are four mechanisms for speciation. The most common in animals is [[allopatric speciation]], which occurs in populations initially isolated geographically, such as by [[habitat fragmentation]] or migration. As selection and drift act independently in isolated populations, separation will eventually produce organisms that cannot interbreed.(Hoskin CJ, Higgle M, McDonald KR, Moritz C , Reinforcement drives rapid allopatric speciation, Nature)

The second mechanism of speciation is [[peripatric speciation]], which occurs when small populations of organisms become isolated in a new environment. This differs from allopatric speciation in that the isolated populations are numerically much smaller than the parental population. Here, the [[founder effect]] causes rapid speciation through both rapid genetic drift and selection on a small gene pool.<ref>{{cite journal |author=Templeton AR |title=The theory of speciation via the founder principle |url=http://www.genetics.org/cgi/reprint/94/4/1011 |journal=Genetics |volume=94 |issue=4 |pages=1011–38 |year=1980 |pmid=6777243}}</ref>

The second mechanism of speciation is [[peripatric speciation]], which occurs when small populations of organisms become isolated in a new environment. This differs from allopatric speciation in that the isolated populations are numerically much smaller than the parental population. Here, the [[founder effect]] causes rapid speciation through both rapid genetic drift and selection on a small gene pool. (Templeton AR, The theory of speciation via the founder principle [http://www.genetics.org/cgi/reprint/94/4/1011] , Genetics)

The third mechanism of speciation is [[parapatric speciation]]. This is similar to peripatric speciation in that a small population enters a new habitat, but differs in that there is no physical separation between these two populations. Instead, speciation results from the evolution of mechanisms that reduce gene flow between the two populations.<ref name=Gavrilets/> Generally this occurs when there has been a drastic change in the environment within the parental species' habitat. One example is the grass ''[[Anthoxanthum|Anthoxanthum odoratum]]'', which can undergo parapatric speciation in response to localized metal pollution from mines.<ref>{{cite journal |author=Antonovics J |title=Evolution in closely adjacent plant populations X: long-term persistence of prereproductive isolation at a mine boundary |journal=Heredity |volume=97 |issue=1 |pages=33–37 |year=2006 |pmid=16639420 |url=http://www.nature.com/hdy/journal/v97/n1/full/6800835a.html}}</ref> Here, plants evolve that have resistance to high levels of metals in the soil. Selection against interbreeding with the metal-sensitive parental population produces a change in flowering time of the metal-resistant plants, causing reproductive isolation. Selection against hybrids between the two populations may cause ''reinforcement'', which is the evolution of traits that promote mating within a species, as well as [[character displacement]], which is when two species become more distinct in appearance.<ref>{{cite journal |author=Nosil P, Crespi B, Gries R, Gries G |title=Natural selection and divergence in mate preference during speciation |journal=Genetica |volume=129 |issue=3 |pages=309–27 |year=2007 |pmid=16900317}}</ref>

The third mechanism of speciation is [[parapatric speciation]]. This is similar to peripatric speciation in that a small population enters a new habitat, but differs in that there is no physical separation between these two populations. Instead, speciation results from the evolution of mechanisms that reduce gene flow between the two populations.<ref name=Gavrilets/> Generally this occurs when there has been a drastic change in the environment within the parental species' habitat. One example is the grass ''[[Anthoxanthum|Anthoxanthum odoratum]]'', which can undergo parapatric speciation in response to localized metal pollution from mines.<ref>{{cite journal |author=Antonovics J |title=Evolution in closely adjacent plant populations X: long-term persistence of prereproductive isolation at a mine boundary |journal=Heredity |volume=97 |issue=1 |pages=33–37 |year=2006 |pmid=16639420 |url=http://www.nature.com/hdy/journal/v97/n1/full/6800835a.html}}</ref> Here, plants evolve that have resistance to high levels of metals in the soil. Selection against interbreeding with the metal-sensitive parental population produces a change in flowering time of the metal-resistant plants, causing reproductive isolation. Selection against hybrids between the two populations may cause ''reinforcement'', which is the evolution of traits that promote mating within a species, as well as [[character displacement]], which is when two species become more distinct in appearance.<ref>{{cite journal |author=Nosil P, Crespi B, Gries R, Gries G |title=Natural selection and divergence in mate preference during speciation |journal=Genetica |volume=129 |issue=3 |pages=309–27 |year=2007 |pmid=16900317}}</ref>