Kat asked in Science & MathematicsBiology · 1 decade ago

AP BIO: Hardy Weinberg and ecology help?

What is the evolutionary significance of speciation and the three processes that cause a population to undergo speciation.

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    1 decade ago
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    Speciation, is caused by natural selection, and is the process by which evolution takes place.

    Example: Darwin's finches (very over-simplified). You have a population of one species of finch that finds itself on an island. Food is limited. Some birds happen to have heavier, stronger bills that are good at opening tough seeds. They are able to pass on this gene because they are able to get into seeds other finches can't. Over time random mutations increase the size and strength of the bill, and eventually there are distinct populations of finches that all have heavy thick bills. At the same time, some finches happen to have thin pointed bills that these finches can use to reach into narrow spots and extract small seeds the heavy-billed finches can't reach. The same random mutations occur, and the ones that cause the bills to be smaller and allow the birds to reach more food, allow them to reproduce and pass on these mutations. Eventually you have two finch populations that are different enough they don't interbreed naturally, and fit our human definition of "species". You may also have an intermediate type, that are able to survive because they can take advantage of both food types, just not as well as the two extremes.

    The Hardy-Wienberg principle explains this same concept.

    The principle states that in an unchanging environment, the gene pool won't change-that the system would be in equilibrium, or static. This only happens in a laboratory situation. For a system to be in equilibrium, mating has to be random, there can't be mutation, no genes are lost or brought into the system through emigration or immigration, the population is large enough to prevent inbreeding, and there are no environmental pressures.

    Species only change when there are disturbing influences (there are more than three processes, so your teacher or textbook may be focusing or combining three of these).

    1. Non-Random Mating: Mating isn't random. Individuals that survive to mate have genetic traits that would be helpful to the next generation. In addition to this, most species have some test of fitness (like a finch being able to prove they can get enough food to give them the extra energy to spend time singing long and loud) to see what mate would be best at providing genes that help the resulting offspring to survive the best.

    2. Mutations: Mutations occur randomly. Sometimes they cause an individual to be less fit to survive, sometimes the mutation is neutral and doesn't influence the fitness, and sometimes it gives the individual an advantage that helps them survive better than other individuals. (Like a mutation that shapes a beak in a way that allows them to get to some food otherwise unavailable).

    3. Environmental Pressure: There are always limited resources. Infinite resources would allow all individuals to survive to reproduce, but this doesn't happen in nature. Individuals that are better at getting the resources are more likely to pass on their genes. (There was a limited amount of food for the finches-not all could survive). Another example of environmental pressures are the ability to escape predation, ability to capture prey, and ability to withstand extremes in temperature or other abiotic factors.

    (the first three are likely the three mentioned in your textbook)

    4. Limited population size: This relates to limited resources-and the idea that not all individuals are able to survive to pass on genes.

    5. Random Genetic Drift: Not all genes are passed on to offspring as genes split and are combined from both parents. There is a random chance that certain genes may not be passed on to the next generation.

    6. Gene Flow: genetic material can be brought in from other populations, and some genetic material leaves the population as individuals move between populations.

    There is a lot of math that explains the effect different pressures have on the expression of a particular allele, but I won't go into it, since this answer is already pretty long. You got me into teacher mode :)

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