Evolution/Isolation and the evolution of new species?
Explain how genetic variation and natural selection result in the formation of a new species in isolated populations?
First, you must understand that isolation comes to an area in many different ways---the change in course of a river, an earth quake that creates a rift, over which no animal or plant can get over, mountain ranges that erupt as the earth buckles, etc. Where there was one large, huge environment, there are now two, or three, or four or more, since the planet remains dynamic. And that isolated area didn't necessarily happen in a short time.... it make have taken billions of years, but isolation has occurred at various places, many, many times in the history of this planet, and will continue to do so in the future.
One of the best places to see isolationism's effects is the Galapagos Islands. Cormorants that came from South America, either by being blown there while in flight, or hitching a ride on drift wood, cormorants in the Galapagos were rid of all of the predators of South America. Thus, wings really were not needed. Remember that wings are expensive to maintain, AND that there is always a mutant born with shorter wings many many times to all birds. Mutations of ALL sorts are experienced by ALL plants and ALL animals in ALL generations ALL the time!! In areas where wings are needed, small wings are a disadvantage... the bird cannot fly away from its enemies, and thus that mutation,in that area, is deleterious, and a bird carrying it never makes it to adulthood to pass on that gene in, say, S. A.
However,because there were no predators on the the Galapagos it was possible for those smaller winged bird to survive.... in fact, the bird had an advantage, now, since bigger wings are more easily damaged than smaller ones. And maintaining huge chest muscles for flight, were no longer needed... just chest muscles for swimming after fish in water. And if evolution continues, and it IS constant, the wings will become smaller and smaller. Enough wing must remain, however, to allow the bird to swim after its prey. Over the next several million years, this isolationism may produce more mutations for the cormorant, and when enough of them are different than the cormorants in S. A., they will be unable to breed, and produce live young. Thus is created a new species of cormorant.
Another example: One pair of tortoise came to one island, and then their offspring migrated to other islands. Foods on each of the islands there demanded different abilities to get it, so on all of the islands, there are some that adapted--either with longer legs, longer necks, and changes to the top part of the shell... (in particular the tortoise with the large rise in the top of the shell was the last of his species...he was called "Lonesome George". Google the name, and along with it you will find the efforts to bring this particular tortoise species back from the brink of extinction.) (All of his species, and likely several we will never know about, were wiped out by humans as sailors stopped there, picked up these animals, put them on ships, upside down, so they'd not be able to move, and were used as fresh meat.
And this isolated condition has produced tortoises that are different species, and cannot breed and produce viable young....they each had been isolated that long.
The general rule is that when enough mutations within a separated species have occurred, that species is different enough from the "parent" species to the extent that interbreeding and viable young don't happen. And by this method, a new species is created.
Species either adapt to their environment or go extinct. Of all the animals and plants that have ever lived on this planet, 99% are extinct. This planet has experienced 5 near mass extinctions because of asteroids. It took millions and millions of years for life to return each time.
Another example of species--this one of a plant occurring by separation is the baobab tree of Africa v. the one on the island of Madagascar. Why do they look so different? They were the same tree before a rift occurred that separated Madagascar as an island from mainland Africa. The pressures for survival in Madagascar were different than those in Africa, and thus a different tree emerged because of those pressures. You would never mistake one for the other.