Speciation: Summary

<h1>Text Preview</h1> <p>slide 1</p> <p>While we can hike across the Grand Canyon, it's an insurmountable geographic barrier to a squirrel. As the canyon grew, it divided one species of squirrel into two populations. The conditions are different on each side of the canyon and the two squirrel populations each adapted to its environment. Scientists are currently debating whether the Kaibab and Abert squirrels should each be considered a separate species. Depending on which definition of species we use, we can consider the squirrels separate species, because they look and act differently, or the same species, because they are still able to mate with each other.</p> <p>slide 2</p> <p>The Grand Canyon is an example of a geographic barrier. Geographic barriers that isolate the gene pool of a splinter population from the parental gene pool can lead to allopatric speciation. Speciation is most likely to occur if the splinter population is small, because the founder effect and genetic drift have the greatest effect on small populations. The gene pool of a splinter population can also be isolated from the parental gene pool by a reproductive barrier. This leads to sympatric speciation.A reproductive barrier can block breeding between species either before or after the formation of a zygote. In both types of speciation, the splinter population is exposed to different conditions than the parental population, so natural selection pushes the gene pools in different directions.</p> <p>slide 3</p> <p>If two related populations that have been geographically separated come back into contact with each other, a hybrid zone may form. In the hybrid zone, the two species may breed with each other, to produce hybrids. A hybrid zone does not expand in size, and gene flow between the two species is restricted to the hybrid zone. </p> <p>slide 4</p> <p>Scientists are currently debating the rate at which speciation occurs. Some believe that speciation occurs gradually. Others believe speciation occurs in short bursts of rapid change, followed by long periods with little change, a theory called punctuated equilibrium. The fossil record supports punctuated equilibrium, because generally we can't find gradual transitions between fossil forms. Supporters of gradual evolution argue that this is because the fossil record is incomplete. We'll need to collect more fossils to determine which theory is correct.</p> <p id="TextCopyright">Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education</p>