BIOL 180 W9 Study Questions
BIOL 180 W9 Study Questions BIOL 180
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This 8 page Class Notes was uploaded by Angel Lee on Tuesday December 8, 2015. The Class Notes belongs to BIOL 180 at University of Washington taught by Scott Rider Freeman in Summer 2015. Since its upload, it has received 182 views. For similar materials see Biology in Biology at University of Washington.
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Biology 180: Study Questions 9 Autumn 2015 1. Consider consumption. a. Alder (a tree species with nitrogen‐fixing bacteria), has a carbon-to-nitrogen (C:N) ratio of 19:1. Willow and poplar, which do not have N‐fixing bacteria, have C:N ratios of 26:1 and 42:1, respectively. If caterpillars are given a choice of eating alder, willow, or poplar, predict the order of species they prefer. Explain why. If the N limitation hypothesis is correct, caterpillars would benefit from eating species with a higher ratio of N. Therefore, caterpillars will prefer to eat alder, then willow, then poplar. b. Recall the mussels in Maine preyed on by crabs. Suppose mussels from high‐predation (HP) and low‐predation (LP) areas of the same bay are swapped (via transplantation at “Start”). Make bar graphs showing the predicted results if average shell thickness, relative to overall body size, is measured 2 years later (“End”) on the transplanted Start: HP End:LP Start: P EndH:P individuals. Height indicate avg shell thickness c. Predict what the offspring (“O”) of the “End:LP” parents will look like in terms of relative shell thickness, if they end up growing in the array of habitats indicated (here NP = no predation). Average shell thickness varies with predation in the offspring because it Parent O in HP O in LP O in NP is an inducible defense! “End:LP” 2. Adenoviruses cause colds. You want to test the hypotheses that 1) adenoviruses induce sneezing in humans to increase their chance of being transmitted to uninfected people, 2) infected hosts sneeze to rid themselves of adenoviruses, and 3) sneezing has nothing to do with viral infection. You have a drug that inhibits sneezing, so you can compare large, random samples of sneezers versus nonsneezers. What you will measure: 1) measure duration and severity of cold symptoms and # of uninfected people infected after contact with individuals in the study. Prediction of hypothesis 1: sneezers will infect many more people than nonsneezers Prediction of hypothesis 2: sneezers will have less severe cold symptoms compared to nonsneezers Prediction of hypothesis 3: there is no difference in number of infected or cold severity between sneezers and non sneezers 3. Define the following terms: • Competitive exclusion principle “species with the same or overlapping niches cannot coexist. If this occurs, the more competitive species will drive the less competitive species out” • Niche “range of resources used by a species” • Resource partitioning “a change in niche caused by competition” • Interspecific competition “competition between different species” • Character displacement “changes in morphological or other traits that increase fitness by reducing competition” 4. Explain how niche (or resource) partitioning could lead to 35 species of insects feeding on same plant species. Natural selection should favor individuals that do not compete with other species for the same food resources. If so, then over time different species should evolve to use different food resources. 5. Suppose a hurricane swept 20 individuals of two lizard species onto the same island. The niches of these two species overlap extensively, but not completely. Predict the fate of the two species on this island over time. Explain the logic behind your prediction. Character displacement should occur the two species should get less alike over time so that they partition resources (have separate niches) and do not compete. 6. Design an experiment to test the hypothesis that Douglas fir and western redcedar have overlapping niches, but that Douglas fir outcompetes redcedar in drier soils while redcedar outcompetes Douglas fir in wet soils. Groups: There will be six plots. 3 with drier soil and 3 with wet soils with the following categories: douglas fir only, redcedar only, douglas fir and redcedar. Control: wind, sunlight, Prediction: Douglas fir and redcedar can grow in both wet and drier soils by themselves. However when they are together, Douglas fir thrives and has a larger population compared to redcedar in drier soils, while redcedar thrives and has a larger population compare to Douglas fir in wet soils. Species A Species B 7 . Fruit fly species A and B lay their eggs in rotting fruit. Initially, their niches are measured as graphed to the right. % resource On the graphs below, plot how their niches used would be expected to change over time if competition is symmetric versus asymmetric— with B as the slightly better competitor. 0 3.5 7 1 .5 Acidity of fruit (pH) Symmetric competition: Asymmetric competition: % resource used 0 3.5 7 10.5 14 0 3.5 7 10.5 14 Acidity of fruit (pH) Acidity of fruit (pH) 8. Recall experiments that showed that mussels increase their attachment strength and shell thickness in response to flows of water from areas occupied by either a crab or broken mussel shells. • Is the change in mussel attachment strength and shell thickness an induced defense or a standing defense? Explain your answer. The change in mussel attachment strength and shell thickness is an induced defense because it occurs in the presence of a predator. • Suppose that crabs are abundant near a mussel all its life, and that it develops an extraordinarily thick shell and high attachment strength as a result. Would these traits be passed on to its offspring? Explain why or why not. No, because the phenotypic change was not the result of a change in genotype, and is therefore not heritable. • You might not consider mussels to be very bright. How do they know that crabs or broken mussel shells are nearby? They must sense a molecule in the water that is released by crabs and a molecule that is released by broken mussel shells. 9. Why do some species have induced defenses while others have standing defenses? Stated another way, under what circumstances would natural selection favor induced defenses rather than standing defenses? Defenses require resources and energy. Natural selection would favor defenses that would protect species in a more efficient manner. Inducible defenses are efficient and favored by natural selection in cases where predators are less common and only needed specifically on approaching a predator. Standing defenses are efficient and favored by natural selection in cases where species constantly exposed to predators or bad conditions. 10. Explain the term "coevolutionary arms race." Specifically, why is an arms race an appropriate metaphor for hostparasite interactions? What is "coevolutionary" about the interaction? “The interaction is coevolutionary because the two interacting species act as selective agents that affect each others’ fitness. It is an arms race because an adaptation that confers an advantage to one species creates a selective advantage for an adaptation in the other species that negates this advantage.” 11. The text describes how snails that are infected by a certain fluke species are more likely than uninfected snails to move into brightly lit areas. The flukes also occupy the snails tentacles and actively wriggle back and forth. Design an experiment to test the hypothesis that snails infected by flukes are more likely to be eaten by birds than uninfected snails. Groups: start with a population of genetically identical snails. Infect half with live flues and the other with dead flukes Follow the individuals in the field. Record how many are eaten by birds. 12. Trypanosomes are parasites. Their life cycle has a stage that occurs in tsetse flies and a stage that occurs in humans or livestock. The parasite is transmitted from one host to another via bites from tsetse flies. Some researchers claim that tsetse flies that are infected with trypanosomes tend to bite hosts more often than uninfected flies. Design an experiment to test this claim. Groups: Start with a large population of newly hatched teste flies, none of which are infected with trypanosomes. Infect one half with live trypanosomes and infect the other half with dead trypanosomes. Measure variable: number of bites on host such as a livestock animal when exposed to infected v. uninfected flies 13. Biologists may begin using naturally occurring fungal diseases of mosquitoes as agents to control malaria. • Why would public health officials focus on mosquitoes to control a human disease? Public health officials focus on mosquitoes because they are the mode of transmission for the disease. By monitoring mosquito populations, they can control the rate of transmission of the disease. • Why might a fungus possibly be a more effective control agent than an insecticide such as DDT? Fungus maybe a more effective control agent because mosquitoes populations may develop adaptations that make them more tolerant to insecticides. A fungal pathogen would have the potential to evolve along with mosquitoes – a coevolutionary arms race might being that would lead to better longterm control of mosquitoes. 14. Consider the Nlimitation, topdown, and defense hypotheses to explain why the world is green. Identify which hypothesis is most likely to be correct in each of the following situations. • Dry conditions have weakened trees in Alaska, making them less able to make sticky sap and poisonous resins. In response, insects called spruce budworms have exploded in numbers and are killing the trees. Defense hypothesis • Caterpillars began defoliating trees in northern Minnesota one summer. The infestation stopped because flies laid their eggs in the caterpillars. When the fly larvae hatched, they ate the caterpillars from the inside out. Top down hypothesis • Aphids make their living sucking sugary sap from plants. They eat almost nothing but sugars (formula C(H O) ). 2 n nlimitation hypothesis 15. Wolves kill coyotes. Why did hawks and mice increase in Yellowstone Park, after wolves were reintroduced? Draw a food web that helps explain your logic. Hawks and mice increased in Yellowstone Park because wolves fed on coyotes which primarily fed on hawks and mice. There was a decrease in predation of hawks and mice. 16. Fill in the chart below to begin the process of designing experiments that would test alternative hypotheses—other than induced defenses—that could explain variation in mussel shell thickness (relative to overall size) among individuals. You will do these experiments in the laboratory. Hypothesis Comparison groups Two conditions that you will control Mussel shell thickness Large, random sample of mussels from the 1. amount of predation is limited by the amount same population: High food availability of nutrition a mussel gets. Large, random sample of mussels from the 2. amount of tide action same population: Low food availability Mussel shell thickness Large, random sample of mussels exposed 1. food availability varies with exposure to to areas with a lot of wave/tide action. wave/tide action. Large, random sample of mussels exposed 2. amount of predation to areas with minimal wave/tide action. 17. Consider the experiment that Connell did on barnacles in the intertidal. Recall that adult Semibalanus (“S”) are found only in the lower intertidal and adult Chthamalus (“C”) are found only in the upper intertidal. a. How would you test the hypothesis that adult S cannot grow in the upper intertidal? I would take S barnacles and grow them in the upper intertidal without the presence of C barnacles. If they are able to survive in the upper intertidal, they have the ability to grow in upper intertidals. b. Graph the fundamental and realized niches of C and S. Label them as follows: Habitat CF = C’s fundamental niche preference CR = C’s realized niche (% of SF = S’s fundamental niche individuals) SR = S’s realized niche 18. If you pollinate Mimulus lewisii individuals that are growing in their natural habitat by hand, the number of seeds produced by the handpollinated individuals is far higher than the number of seeds produced by individuals that are pollinated by bumblebees. From these data, biologists conclude that intense competition is occurring for pollinators. Explain their logic. Hand pollination data show that the fitness of mimulus indviduals is limited by their access to pollen and or their ability to get their pollen to other individuals. Because pollinators, as a resource, are in short supply and have a large impact on fitness, there should be intense competition to attract more pollinators. Better competitors will have higher fitness. 19. If a grasshopper ingests a hairworm egg, the hairworm grows inside the grasshopper. When the hairworm is sexually mature, the grasshopper throws itself into a pond or lake. Grasshoppers live on land and cannot swim. Once in the water, the adult hairworm leaves the grasshopper and swims away; the grasshopper drowns. a. In hairworms, predict where sexual reproduction and egglaying take place: land or water? Water. b. Research has shown that sexually mature hairworms release signaling molecules into the brains of grasshoppers. The signaling molecules affect grasshoppers when they bind to specific proteins on nerve cells in the brain. Using this information, predict how natural selection will act on grasshoppers in habitats where hairworms are common. In habitats where hairworms are common, natural selection will select for alleles that block or inhibit the binding to specific proteins on nerve cells and select against alleles that do not have this ability. 20. In humans, the number of new or “emerging” diseases caused by viruses, bacteria, or other parasites has been increasing dramatically over the past 50 years. The following three factors have been proposed to explain this pattern. Explain the logic behind each. a) Human populations have exploded; most animal populations are now in direct contact with humans. Chances of transmission are higher, especially for parasites that previously infected other species of animals. . b) Ocean and atmospheric temperatures have undergone large increases. Warmer climates tend to have more parasites and more types of parasites; with climate change the geographic range of warmweather parasites is increasing. c) There are more biomedical scientists alive now than ever before. There is ascertainment bias or the actual number of new diseases isn’t increasing, its just that we’re more likely to detect new diseases now than we were in the past, because there are more skilled people around to do the detecting. 21. In Central America, an ant species lives inside the thorns of Acacia cornigera trees. A. cornigera leaves secrete a sugary solution and make proteinrich structures that the ants eat. Design an experiment to test the hypothesis that the relationship is mutualistic (meaning, mutually beneficial in terms of fitness)—specifically, that ants reduce herbivory on A. cornigera by attacking caterpillars. Test group: cornigera trees with vary amounts of ants Measured variable: herbivory or leaves eaten by caterpillars Prediction: if the interaction between the cornigera tree and ants are mutual, as ants consumes photosynthae, the herbivory by caterpillars should decrease with the presence of ants. Make and label a graph showing the results Make and label a graph showing the results predicted under the mutualism hypothesis: predicted if the relationship is actually parasitic. Herbivory/ Herbivory/ leaves leaves consumed by consumed by caterpillars caterpillars 22. Consider the population pyramids for the United Size of ant population from 0 to 100 from 0 to 100 States, given here. • On the 2000 data, label the area that conforms to the "baby boomers. • On the 2000 data, label the area that conforms to the "baby boom echo"--meaning the children of baby boomers. • Examine all three graphs. Is the sex ratio (proportion of males versus females) roughly the same or very different for children under 5? Is the sex ratio the same or very different for adults over the age of 65? • Examine the number of young children being added to the population in 2000, 2025, and 2050. Based on these data, is the U.S. population growing quickly because of increased birth rates? Yes • A comparison of the 2000, 2025, and 2050 graphs indicates that the U.S. population is expected to increase rapidly. Will most of this growth be due to increases in birth rate or immigration? Immigration; changes in birth rate cannot explain increase. 23. Consider the geographic structure of natural populations. • What is a metapopulation? Population of populations – a group of relatively small and geographically isolated populations. • When biologists first explored the dynamics of metapopulations, it was out of purely theoretical interest. But now the topic is considered of urgent practical importance. Why? Humans are fragmenting many natural habitats, thus forcing organisms in to a metapopulation structure. • In terms of metapopulation dynamics, why is it important to save unoccupied habitat and construct “wildlife corridors” between habitats used by endangered species? Unoccupied habitat: needed to that individuals can colonize new sites and start new populations. Wild life corridors: needed so that individuals can move from one population to another; gene flow will reduce effects of inbreeding and drift in isolated populations. 24. These Douglas fir population pyramids are from 3 sites: one that was logged and replanted to Douglas fir, one where succession has been allowed to occur naturally (Douglas fir is a mid to latesuccessional species), and an old growth forest. Identify which graph is from which site. In each case, explain your logic. NOTE: the width of the bars indicates that relative abundance of each age class. Age classes are in years. 700+ 60 600 50 50 500 40 40 400 30 30 300 20 20 200 10 10 100 Site: natural succession Site: logged and replanted Site: old growth forest Logic: the age strucLturic:beucduindthaettaensihareasbngnpkolelatindptaeterreligitehthinefpopswlntoerwdbthdabmeestfiu 25 This graph is an alternative way to show age structure in populations— it’s a population pyramid tipped on its side, with males and females combined. These data are from a fish that breeds from age 3 until death. The solid line predicts the number fish that should be in each age class, given the number of individuals aged 12 and older. What is maximum observed lifespan? 36 Circle the interval of time when the population was doing particularly badly. Why are there so few 02 year olds, compared with the predicted number? Many fewer 3 to 11 years old are breeding than expected. 26. Create a population pyramid for the following populations of western hemlock trees. Note that hemlocks have a maximum lifespan of ~500 years, with high survivorship at every age class until a rapid decline after 350 years. In each case, the population size for individuals 050 years old is indicated. Population growth had been 0 for Population growth had been 0 centuries, but logging just for centuries, but NO reproduction removed all trees >200 years old. occurred during a 10year drought 230240 years ago. (Reproduction then returned to previous levels.) 500 500 450 450 400 400 350 350 300 300 250 250 200 200 150 150 100 100 50 50 27.Consider the age structure of populations. Draw a population pyramid for a human population where r is 0. In this population, survivorship is high from just after birth until age 65, when it declines rapidly. In birds, survivorship is constant throughout life—the same fraction of a cohort dies at every age. Draw the population pyramid that results, in a population of constant size (r = 0).