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Regents Living Environment 16-3: The Processes of Speciation Oswego High School Natural selection and chance events can change the relative frequencies of alleles. Speciation, the formation of a ___________ _________________ occurs as a result of these changes in allele frequency. Species: ________________________________________________________ ________________________________________________________________ Since a population of a species has a _________________ gene pool, if a change occurs, it can ____________ to other individuals in the population and those individuals will ___________________. Speciation occurs through various ________________ _____ _______________. Isolating Mechanisms In order for speciation to occur, the gene pools of two populations must become _____________________. Reproductive Isolation Reproductive isolation happens when members of two ____________________ populations cannot __________________with each other and produce fertile offspring. At this point these populations have ______________ gene pools. Behavioral Isolation Behavioral Isolation occurs when two populations are ______________________ of interbreeding, but may have different ___________________ rituals or other reproductive strategies that involve _________________. Example: Habitats of Eastern and Western meadowlarks ________________ with each other. However, these birds have very different ________________ ____________. Eastern and Western meadowlarks will not respond to each other’s mating calls. Geographic Isolation Occurs when tow populations are separated by __________________________ _____________________ like rivers, mountains or bodies of water. Example: About 10,000 years ago the Colorado River split the Albert Squirrel into two _____________________ populations. This resulted in two separate gene pools being formed. Natural selection worked ____________________ and led to the formation of a sub-species called the ______________ ______________. These two squirrels are closely related, but differ in many ways. Albert Squirrel Kaibab Squirrel Geographic isolation does not always __________________ formation of a new species. It is possible that lakes can become connected during ______________ or _______________ _______________ may form between islands. This may allow separated populations to __________. If two separated populations can still ___________________, they are still of the _____________ species. Also, barriers can separate certain types of organisms but not others. Temporal Isolation Temporal isolation occurs when two or more species reproduce at ___________ times. Example: Three similar species of _________________live in the same area of rain forest. Each of these orchids ___________________ on different days, so they will never pollinate each other. Testing Natural Selection in Nature Natural selection can be observed in nature. When Darwin first saw the Galapagos Finches, he thought they were all _________________ birds. Because they looked so ___________________ from one another. Once he realized they were finches, Darwin proposed that they had evolved from a common _________________. This was a very reasonable hypothesis, but nobody thought it was _________________ until ________________ and __________________ ____________, who spent 20 years studying these finches. They realized that Darwin’s hypothesis relied on two testable assumptions. 1. In order for beak size and shape to evolve, there must be enough ________________ ________________ to provide raw material for natural selection. 2. Differences in beak size and shape must produce differences in ________________, which will cause natural selection to occur. The Grants studied medium ground finches on _____________ _____________, one of the Galapagos Islands. Variation First, the Grants ____________________ and __________________ as many individual finches as possible. They recorded those who were still ____________ and those how had _____________. They also studied many anatomical characteristics. These characteristics appeared in a __________ _________________ distribution, which led the Grants to conclude that there was a great deal of __________________ of _____________________ traits. Natural Selection Many researchers didn’t see the different finches __________________ or eating ______________ foods. This is because when they visited, it was the rainy season and there was ______________ of food. However, when the dry season came, some food became ____________, while other food sources ________________ altogether. During this time, beak size can be the difference between ____________ and _____________. In order to survive, birds become feeding ________________, meaning that each bird will select the type of food best ______________ for its beak size. The Grants discovered that individual birds with different sized beaks had _________________ chances of survival during a drought. They found that individuals with the _______________ beaks had the best chances of survival when food was scarce. Also, large beaks had a role in ________________. Large beaked finches mate with other large beaked finches. Because of this, the average beak size ______________ in the population in a dramatic way over the course of time. This increase in average beak size is an example of ____________________ __________________. By documenting this change, the Grants were able to provide _______________ for the process of evolution and that it can happen _____________. This was very different from what Darwin envisioned, which was that evolution happened __________________. Speciation in Darwin’s Finches If we can combine what we have learned in this chapter, we can show now natural selection can lead to ___________________. 1. Founders arrive Many years ago, a small group of finches from the South American mainland _____________ on the Galapagos Islands. We will call this group Species A. Finches are small and cannot fly far distances over open water. This means they must have been __________ there by a storm. Once they got to one of the islands, they were somehow able to ________________ and _________________ 2. Geographic isolation Some finches from Species A moved to another island in the Galapagos. Since they don’t usually fly over open water, they _____________ move from island to island. These two finch populations were now __________________ from each other and no longer shared a gene pool. 3. Changes in the Gene Pool Over time, the populations on the two islands _________________ to their new environments. The first island may have had small, ___________ shelled seeds, while the second island may have had large, _________________ shelled seeds. Directional selection would have favored those with _______________ beaks. Over time, this population would have evolved larger beaks, leading to the formation of a _______________ _____________________, population B. 4. Reproductive Isolation Imagine that a few birds from population B were to return to the first island. It would be very ______________ that birds form Species A would breed with birds from Species B. Finches choose their mates very _________________. Finches choose to mate with finches with the ______________ beak size as they have. Differences in beak size combined with ____________________ rituals leads to reproductive isolation. The ______________ _____________ of the two populations remain _______________, even though they live in the same place. Because of this reproductive isolation, the two populations have now become _______________ species, Species B. 5. Ecological Competition As Species A and B live in the ____________ environment (the first island), they will ________________ with each other for available food. During the dry season, those who are most ______________ from each other will have the highest __________________. More specialized birds have ______________ competition for certain types of seeds and other food sources. The competition among _________________ finches is also reduced. Over time, the birds form Species B on the first island may _______________ into a new species, Species C. 6. Continued Evolution This process of isolation, genetic change, and reproductive isolation __________________ itself across the entire island chain of the Galapagos. Over many generations, this led to the evolution of the __________ different finch species that live on the Galapagos Islands. Studying Evolution Since Darwin Darwin made very _____________ assumptions about heritable variation, the age of the Earth, and relationships among organisms. New _____________ from physics, biochemistry and genetics could have proved Darwin _______________, but they didn’t. Scientific evidence supports the theory that living species descended with _____________________ from common ancestors. Limitations of Research The Grants’ research shows the effects of directional selection, as well as how competition and climate change affect natural selection. However, their work does have some __________________. Even though the Grants observed changes in _____________ ______________ of the finches, they did not observe the formation of a new _________________. Unanswered Questions The Grants’ studies fit into an _____________________ body of scientific research that _______________ the theory of evolution. Remember that a theory is a well supported, __________________ explanation of natural phenomena that accounts for a __________________ range of observations. The theory of evolution fits this definition. New discoveries have led to new ____________________ that ______________ or _________________ Darwin’s ideas. However, there are many questions that remain unanswered. Understanding evolution is important because it is still _____________________ to this day. Evolution drives changes like ______________ ________________ in bacteria and viruses and ___________________ resistance in insects. Understanding evolution helps us _______________ to these changes in ways that ______________ human life.