Week 1 review questions ANSWERS

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Week 1 review questions ANSWERS Powered By Docstoc
					Biology 140: ecology and evolution
Week 1 review questions

Instructions: These questions will NOT be collected; they are for your own studying
purposes. I strongly suggest that you do the weekly review questions each week, and use
them to assess your own understanding. They will also come in handy as you study for
the exams!

Part 1: Vocabulary terms to know and love. Be able to define each of these terms in a
sentence or two. If a word has a “general purpose” meaning and a specific scientific
meaning, I am looking for the latter.

Evolution: change in allele frequencies in a population over time
Adaptation: a heritable trait that increases the fitness of an individual in a particular
      environment, relative to individuals lacking the trait.
Proximate explanation: A functional explanation for an ecological pattern or process—
      for example, if you asked some trees have scaly/flaky bark, the proximate
      explanation may have to do with cell death, tissue senescence, and/or shedding bark
      infected with fungi or bacteria.
Ultimate explanation: How it got to be that way—usually invokes evolutionary
Transitional form: a species with traits that are intermediate (transitional) between older
      and younger forms. Generally used to refer to fossil species.
Vestigial traits: Traits that are reduced in size or function compared to ancestral species.
      Examples include eye buds in sightless cave-dwelling species, tail bones in humans,
      finger bones in whale flippers.
Homologous: Two traits, structures, or genes are homologous if they are similar by virtue
      of having descended from a common ancestor with that trait. Examples include
      vertebrate forelimbs, certain gene families (see your text), developmental pathways,
Analogous: Two traits or structures are analogous if they have similar function as a result
      of convergent evolution, not because of shared ancestry.
Convergent evolution: Evolution of similar traits in distantly related species as a result of
      common selective pressures—adaptation to similar environments or ways of life.
Darwinian fitness: Reproductive success—the number of surviving offspring produced
      by an individual.
Uniformitarianism: in geology, the principle which states that the geological processes
      are constant throughout time
Essentialism: the philosophy that all species are unchanging throughout time; every
      species has an “essence” which characterizes all aspects of that species
Natural Theology: the study of nature to understand the workings and creation of God
Phylogeny: a family tree of populations or species; the evolutionary history of a
      particular group of species
Part 2: Review and application of concepts
    1. How did scientists‟ concept of what a species is change with the acceptance of the
        theory of evolution? Species were seen as being fixed, unchanging, and
        independently created. Evolution implied that species commonly changed over
        time, and that they were not independently created. Rather, species descended
        from common ancestors.

   2. Compare and contrast ultimate and proximate explanations—be able to do this
      with an example, for example by providing an ultimate and proximate explanation
      for scaly bark on some trees (paper birch, for instance) or any other phenomenon
      of interest—medical phenomenon are a good way to play with the distinction—
      e.g., proximate and ultimate causes of illness!). In general, ecological
      explanations are proximate, and evolutionary ones are ultimate. An ecological
      explanation for flaky bark would point to genetic, chemical, or ecological
      factors— programmed cell death, flaking off of tissue infected with fungal spore,
      etc. An ultimate (evolutionary) explanation might focus on why that key trait—
      flaky bark—arose and the explanation will include the phrase “The fitness
      advantage of this trait is. . . .”.

   3. Evidence for evolution emerged from a number of sources. For each general
      source of information below, be able to (a) describe specifically how that type of
      evidence was important in leading to the development of a theory of evolution,
      and (b) provide a specific example of that kind of evidence. (For example, what
      is an example of a vestigial trait that provides insight into evolution?)

Type of evidence:             How it contributed:            An example:
Fossil record                 Indicated patterns of          Transitional forms
                              change in species through      indicated that species with
                              time. Also provided            one kind of traits could
                              evidence of relatedness.       change over time into
                                                             species with other kinds of
                                                             Extinction—showed that
                                                             species were NOT fixed.
                                                             Environmental change—
                                                             fossil record indicated that
                                                             conditions on earth have
                                                             changed over time, which
                                                             suggests a cause for
                                                             changes in species’ traits.
                                                             “Law of succession”, in
                                                             which fossil species were
                                                             found to exist near similar
                                                             closely allied extant species,
                                                             argues for the relatedness
                                                            of species.
Vestigial traits               Indicate that species traits Eyelessness in cave-
                               can change through time—a dwellers, bone structure in
                               species with eye buds but no whale flippers or bat wings
                               sight might logically be     (vestigial fingers), goose
                               seen to have at one point    bumps, tail bone. (For each
                               been a sighted species with you would want to explain
                               full eyes.                   exactly what it suggests…)
Homologous structures          Indicate that species have   Tetrapod forelimb—bone
                               common ancestry              structure consistent across
                                                            vertebrates, similar to that
                                                            of the first tetrapod that is
                                                            the common ancestor.
Biogeography                   Indicates that species have  Understand Fig. 24.6 in
                               common ancestry              Freeman

4. Darwin often referred to his theory as “descent with modification”. Explain this in
    terms of our modern understanding of evolution. What‟s descending? From what?
    What‟s being modified? How? What Darwin meant is that species evolve one from
    another (i.e., modern species are descendents of fossil species). The “modification”
    refers to changes in traits produced by natural selection: an ancestral trait—
    production of nectar, to take one of Darwin’s examples, is modified by the action of
    natural selection, which acts on variability in that trait. The species’ characteristics
    thus change over time, modified by the action of natural selection.

5. One of Wallace‟s most important insights was expressed in an 1855 paper: “Every
    species has come into existence coincident in space and time with a pre-existing
    closely allied species”. Explain this observation and articulate what this observation
    demonstrates about evolution. ? This statement is the outcome of all of his
    biogeographic observations. This observation argues for descent from a common
    ancestor. If species were created by a divine creator, Wallace argues, then there
    would be no particular reason for the flora and fauna of nearby places to be similar
    and that of distant places to be different. The observation that birds of New Guinea
    and Aru Island are similar to each other but different from those of Borneo, for
    example, is better explained by evolution from a common ancestor. Another way to
    think about this is that if evolution by natural selection has been the process causing
    speciation and diversification on life, then you would expect that similar niches to be
    occupied by related species in nearby areas, and not in distant areas.

6. Explain each of the following observations (a) using Lamarck‟s theory of evolution
    and (b) using the theory of evolution by natural selection.
            a. After the industrial revolution, moths living in or near polluted cities
               changed from being light-colored to being dark-colored. Lamarckian:
               Moths living in polluted cities needed to hide themselves against polluted
               (hence darker) tree trunks to avoid predators, so they developed, during
               their lifetimes, darker coloration. Those acquired traits were passed
              along to their offspring. Darwinian: Darker colored moths had an
              advantage as pollution worsened, because they blended in better with
              polluted tree trunks on which they rested. Those darker-colored moths
              thus had higher survival rates, and as a result left more offspring, than
              lighter-colored individuals. Because color is heritable in moths, that
              resulted in a greater abundance of darker-colored offspring. The
              incidence of dark coloration thus rose over time during the industrial
           b. The incidence of drug-resistance in the bacterium that causes tuberculosis
              is on the rise. Lamarckian: TB bacteria that encounter antibiotics during
              their lives acquire resistance; this resistance is passed along to their
              offspring. Darwinian: There is existing variation for susceptibility to
              antibiotics. Bacteria that are not susceptible (i.e., that are resistant) to
              antibiotics are more likely to survive and reproduce than those that are
              susceptible. Since resistance is heritable, the offspring of those bacteria
              will also be resistant. The frequency of resistance will thus increase from
              generation to generation.

7. What insight did both Darwin and Wallace derive from reading Malthus? Why was
   this insight so crucial? That more offspring are produced than can survive. This
   insight was important because it highlighted for both of them the “struggle for
   existence” that most species experience, and created a mechanism by which some
   species would do better than others.

8. What are the four “postulates” of the theory of evolution by natural selection? See
   your text, page 490. It boils down into the following: (1) individuals vary, (2) some
   of that variation is heritable, (3) more offspring are produced than can survive;
   there is variation in reproductive success, (4) that variation is non-random- in a
   given environment, organisms with particular traits will be more successful. Their
   offspring will have those traits, which will thus increase in frequency over time.

9. Make sure that you can do the “You should be able to…” items on page 495 of your

10. One of Darwin‟s assumptions is that individuals that are “different” in some way
     have an advantage in competition. Why would this be so? Because they may use
     slightly different resources than other individuals. We’ll talk more about the
     specifics of how this works in a few weeks!

11. (Straight from your text—Q. 2 of the Test Your Understanding) “Some biologists
     encapsulate evolution by natural selection with the phrase „mutation proposes,
     selection disposes‟. Explain what they mean, using the vocabulary of natural
     selection.” (Freeman, Biological Science, 3rd Edition, pg 501). Mutation is the
     source of heritable variation—in other words it is the mechanism by which new
     alleles (and, hence, new phenotypes) are generated. Mutation thus creates the “raw
     material” of variability—it “proposes” different forms of a trait, for example.
    Natural selection acts on that variability: favorable variations—those that increase
    an individuals fitness—will increase in frequency, and unfavorable ones—those that
    decrease an individual’s fitness—will decrease in frequency. Or, in other words,
    natural selection will “dispose” of them.

12. What insight did Darwin gain from his observations of the finches in the Galapagos?
    Beak of the Finch, page 30—their variability struck him, and suggested to him the
    relatedness of similar species.

13. David Lack visited the Galapagos long after Darwin (in the 1930s) and made
     carefully observations of the finches. Read the passage about Lack‟s insights in the
     Beak of the Finch, Chapter 4 (pages 54-56). What important pattern did he observe,
     and what did it lead him to conclude? David Lack observed that the beaks of finch
     species that share an island tended to be more different from one another than when
     they were found in isolation. This led him to conclude that competition prevented
     two overly similar species from co-existing and he thus inferred that natural
     selection had driven the divergence of beaks when finches competed.

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