Explain the 2 types of speciation and include what types of isolation produces them?

Allopatric Speciation


Sympatric Speciation


Geographical Isolation


Sexual IsolationExplain the 2 types of speciation and include what types of isolation produces them?
Allopatric Speciation is speciation that occurs when there is a natural barrier that seperates a population. For example, the forming of the Grand Canyon split a population of squirrels in half and because they are now in different locations they will evolve into two seperate species. Large bodies of water, canyons, etc. can all be included in the ';natural barrier'; category.





Sympatric Speciation is speciation that occurs with no physical barrier, but rather the organism just chooses different parts of the same area. For example, going back to the squirrel example: if a population of squirrels all live on one island with NO barrier, then most likely they will no speciate. However, if one day some of the squirrels choose to live at the top of the trees and the other squirrels want to live on the ground-- well then, they can speciate. ';Sym'; means ';same';-- so it's speciation occuring in the SAME area.Explain the 2 types of speciation and include what types of isolation produces them?
It's a bit like a character in a movie going off and having adventures that change him so drastically that when he returns, the folks in his hometown no longer recognize the way he looks and behaves. The biological equivalent is ';allopatric speciation,'; an evolutionary process in which one species divides into two because the original homogenous population has become separated and both groups diverge from each other.





In their separate niches, the two groups go their own evolutionary ways, accumulating different gene mutations, being subjected to different selective pressures, experiencing different historical events, finally becoming incapable of interbreeding should they ever come together again. For many years this has been regarded as the main process by which new species arise.





Often this type of speciation occurs in three steps. First, the populations become physically separated, often by a long, slow geological process like an uplift of land, the movement of a glacier, or formation of a body of water. Next, the separated populations diverge, through changes in mating tactics or use of their habitat. Third, they become reproductively separated such that they cannot interbreed and exchange genes.





Under normal conditions, genes in a given population are exchanged through breeding, so that even if some variation occurs, it is limited by this ';gene flow.'; But gene flow is interrupted if the population becomes divided into two groups. One way this happens is by ';vicariance,'; geographical change that can be slow or rapid.





An example of vicariance is the separation of marine creatures on either side of Central America when the Isthmus of Panama closed about 3 million years ago, creating a land bridge between North and South America. Nancy Knowlton of the Smithsonian Tropical Research Institute in Panama has been studying this geological event and its effects on populations of snapping shrimp. She and her colleagues found that shrimp on one side of the isthmus appeared almost identical to those on the other side -- having once been members of the same population.





But when she put males and females from different sides of the isthmus together, they snapped aggressively instead of courting. They had become separate species, just as the theory would predict.





Unlike the previous modes, sympatric speciation does not require large-scale geographic distance to reduce gene flow between parts of a population. How could a randomly mating population reduce gene flow and speciate? Merely exploiting a new niche may automatically reduce gene flow with individuals exploiting the other niche. This may occasionally happen when, for example, herbivorous insects try out a new host plant.





For example, 200 years ago, the ancestors of apple maggot flies laid their eggs only on hawthorns鈥攂ut today, these flies lay eggs on hawthorns (which are native to America) and domestic apples (which were introduced to America by immigrants and bred). Females generally choose to lay their eggs on the type of fruit they grew up in, and males tend to look for mates on the type of fruit they grew up in. So hawthorn flies generally end up mating with other hawthorn flies and apple flies generally end up mating with other apple flies. This means that gene flow between parts of the population that mate on different types of fruit is reduced. This host shift from hawthorns to apples may be the first step toward sympatric speciation鈥攊n fewer than 200 years, some genetic differences between these two groups of flies have evolved.
Allopatric speciation involves a geographic barrier. gene flow stops due to the barrier, and variations arise from genetic drift and directional selection. Types of isolation: introduction of a geographical barrier, for example a river that has been redirected and is now seperating members of a population. (im sure you can think of other examples like that)





Sympatric speciation occurs when members of a population acheive reproductive isolation without a geographical barrier being present. Best example being found in plants, by means of polyploidy. Also possible by hybridization between two species resulting in doubled chromosome number. back crosses with diploid parents result in sterile offspring. hope that helps.