# Unit 8 Progress Check: MCQ Biology 30 AP - Population And Community Dynamics

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In the mid-1920s, gray wolves, Canis lupus, were eliminated from Yellowstone National Park in the northwestern United States. Over the course of 1995 and 1996, 31 wolves from Canada were relocated to the park. Researchers have tracked the growth of the wolf population from 21 in 1995 to 108 at the end of the study in 2016 (Figure 1). Figure 1. Yellowstone National Park annual wolf population from 1995 to 2016 The wolves prey on large herbivores, primarily elk. The carcasses of wolf kills are a valuable food source for coyotes, Canis latrans. When coyotes are feeding on carcasses, they may be chased off the carcass and/or killed by wolves. Coyotes also hunt small mammals for food. Researchers were studying the effect of wolves' presence on the behavior of coyotes. Researchers observed coyotes in a specific area of Yellowstone National Park and recorded the proportion of the coyotes' time spent on five different activities when wolves were present in the study area and when wolves were absent (Figure 2). Figure 2. Coyote behavior in the presence and absence of wolves. Error bars represent a confidence interval of 95% (Â±2 standard errors of the mean). Based on information in Figure 1, which of the following is closest to the annual growth rate of the wolf population in Yellowstone National Park from 1996 to 2004 ?
B = 17 wolves per year: The equation for calculating a rate is dY/dt, which is the difference in the variable on the y-axis divided by the difference in the variable on the x-axis. In this case, that equation becomes annual population growth rate = (final population size - initial population size)/(number of years). According to Figure 1, in 1996 the population was 36 wolves, and 8 years later, in 2004, the population was 171 wolves. Therefore, (171âˆ’36)/8=16.875, which can be rounded to 17 wolves per year.
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Related to Question 1 Information: Based on the data in the figure, a student claimed that since 2007, the carrying capacity of wolves in Yellowstone National Park has been 100 wolves, and the maximum annual per capita growth rate of gray wolves is 0.6 wolves per wolf per year. Which of the following is closest to the calculated wolf population size in 2017 based on the student's claim?
B = 103: According to the logistic growth model, the change in population size (dN/dt) can be calculated using the equation dN/dt=rmaxN((Kâˆ’N)/K). According to the student's claim, rmax=0.6 wolves/year and K=100 wolves. From Figure 1, N=108 wolves in 2016. Therefore, dN/dt=0.6Ã—108Ã—((100âˆ’108)/100)=âˆ’5.184. The -5.184 needs to be added to the 2016 population size to get the population size for 2017: 108+(âˆ’5.184)=102.816108+(âˆ’5.184)=102.816, which is rounded to 103 to get the final answer.
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Related to Question 1 Information: Identify the independent variable for the experimental results shown in Figure 2.
A = The presence of wolves: The independent variable is selected by the researchers, and the researchers test its effect on the dependent variable. In this experiment, the researchers were looking at the effect of wolves' presence on the behavior of coyotes. Therefore, the presence of wolves is the independent variable, and the behavior of coyotes is the dependent variable.
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Related to Question 1 Information: Which of the following best describes the change in coyote behavior in the presence of wolves?
C = Decrease, No Effect, No effect, Increase, Increase: According to Figure 2, in the presence of wolves (white bars), the proportion of time spent on rest is less, the proportion of time spent feeding on carcasses is more, and the proportion of time spent on vigilance is more than in the absence of wolves (gray bars). Although the mean proportion of time spent on travel increases in the presence of wolves, the error bars overlap, showing that the difference is not statistically significant.
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Final problem related to Question 1: Following the reintroduction of wolves to Yellowstone National Park, researchers measured the mean height of young aspen trees in upland and streamside areas. Which of the following is the most likely cause of the change in mean aspen height from 1998 to 2010 ?
A = The reintroduction of wolves led to a decrease in the population of elk, allowing aspen trees to grow taller: Top carnivores are keystone species, meaning they have a larger role in maintaining an ecosystem than would be expected by their population size. After wolves were eliminated from Yellowstone National Park, the population of elk rose dramatically. The high elk population led to the overgrazing of plant species, including aspen. With the reintroduction of wolves, the elk population has declined, allowing plant species to recover.
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Meerkats live together in groups to help raise and protect their offspring. Meerkat pups are most vulnerable when they are away from their burrow foraging for food. Adult meerkats exhibit sentinel behavior, standing upright and making alarm calls to warn other members in the group that predators are nearby. In a study of meerkat behaviors, scientists observed meerkat foraging groups and recorded the presence or absence of pups along with the frequency of adult sentinel behavior. The scientists determined that sentinel behavior increased when pups were present in the foraging group. Which of the following correctly identifies the dependent and independent variables in the described study?
B = The presence of pups is the independent variable, and the frequency of sentinel behavior is the dependent variable: The scientists are studying the relationship between the presence of pups (independent variable) and the frequency of sentinel behavior (dependent variable).
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Figure 1 shows a food web that describes the relationships within a community containing nine species. Each circle represents a separate species. The size of the circle represents the population size of the species relative to other species in the same trophic level. Figure 1. Trophic relationships among organisms in a community Based on the information in Figure 1, which of the following best predicts a short-term effect of removing secondary consumer X from the community?
A = No Consumer X and a significantly larger white striped circle (for the primary consumer), with two much smaller circles under it: If secondary consumer X is removed, then the leftmost primary consumer will increase in number. Consequently, the two producer species that this primary consumer eats will decrease in number. Note that disturbance events that remove a secondary consumer species can cause large shifts in community composition when the trophic web consists of only a few strong links instead of many weak links.
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Bt corn varieties are genetically modified to produce a toxin that specifically kills corn borers, a type of insect that eats and damages corn crops. Insects that are not closely related to corn borers are not affected by the toxin. Figure 1 shows the increasing production of Bt corn varieties and the change in the use of broad-spectrum pesticides that were the primary means of killing corn borers before the invention of Bt corn. Figure 1. Relative use of pesticides on corn fields and percent of Bt corn in crops How do the data in Figure 1 support the alternative hypothesis that increased use of Bt corn reduces the impact of corn farming on the natural environment?
B = The toxin in Bt corn kills only the corn pests, leaving other insects unharmed: Bt corn is modified to be toxic to certain insects; thus, it doesn't require as much insecticide. The graph shows this trend.
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A biologist was investigating the effects of herbivory on the amount of nicotine produced by the leaves of tobacco plants (Nicotiana rustica). Six groups of plants were grown from seed in the same greenhouse with identical environmental conditions. Three groups were then each exposed for a different interval of time to tobacco hornworms (Maduca sexta), which feed on the foliage of tobacco plants. The amount of nicotine present in the leaves was measured at the beginning and end of each time interval. As a control, the other three groups were not exposed to hornworms. The results of the experiment are summarized in Table 1. Which of the following correctly identifies the dependent variable and the independent variable for the experiment?
D = The dependent variable is the percent change in the amount of nicotine, and the independent variable is the time interval the plants were exposed to the hornworms: The change in the concentration of nicotine is the factor being studied and is therefore the dependent variable. The time interval the plants were exposed to the hornworms is changed by the biologist and therefore the independent variable.
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Figure 1 shows the population fluctuations of phytoplankton and zooplankton in the eastern Pacific Ocean over the course of six years. The major dip in phytoplankton was attributed to a lack of nutrients for phytoplankton. Of the following, which explains why the zooplankton also dipped during the same year and then seemed to cycle over the next three years?
D = The reduction in the phytoplankton population meant that the zooplankton's energy source was drastically reduced, leading to the decrease in the zooplankton population size. After the dip, the phytoplankton provided a steady energy source, and the zooplankton population fluctuated around its carrying capacity: The energy source of zooplankton is the carbon compounds fixed by phytoplankton. Without the proper inorganic nutrients, the phytoplankton population is limited in its photosynthetic activity, leading to an energy deficit in the zooplankton populations. It is also correct that the annual fluctuations in zooplankton represent a stable population cycling around its carrying capacity.
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Bison in Yellowstone National Park have a food-limited carrying capacity that determines how their population grows. If the population grows too large, some bison will either starve or migrate to search for more food. The park is able to support a maximum population of 4,500 bison. Park conservation officials must watch the population and prevent the bison from overpopulating, since they would migrate to nearby farms, causing agricultural damage and creating hazards to drivers. The bison begin to migrate when the population reaches 4,000 because of competition for food. If the current population size of bison is 3,652 and the maximum growth rate of the population is 0.28, calculate the population size after one year and determine whether the park will need to take measures to control the population.
A = The population will be 3,845 after a year. The bison will not pose a problem until the following year, and no conservation action will need to take place: dN/dt=rmaxN((Kâˆ’N)/K) should be used to determine the one-year change in population size: 0.28Ã—3,652((4,500âˆ’3,652)/4,500)=193. Adding 193 to 3,652 projects a population of 3,845, so the population will not reach the point at which bison migration occurs. However, it will reach a level to initiate migration the following year.
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Climate change can affect oceanic ecosystems and their food webs. In the East China Sea (ECS), three major climactic events were considered: the Pacific Decadal Oscillation (PDO), the East Asia winter monsoon (EAWM), and the El NiÃ±o Southern Oscillation. Figure 1 shows the relationships among these climactic events, surface sea temperature (SST), amount of phytoplankton, and copepod abundance. Copepods are important primary consumers in this ecosystem, and many species of fish depend on copepods as a food source. Solid arrows on the diagram indicate a statistically significant effect. The thicker the arrow, the greater the effect. Dashed arrows indicate statistically insignificant relationships. Figure 1. Structural equation model deciphering interactions among climate, phytoplankton, and copepods in the southern East China Sea. Solid arrows indicate significant effects, with the thickness of the arrow reflecting the relative effect. Dashed arrows indicate inconsequential effects. What do the data in Figure 1 suggest about a null hypothesis that the East China Sea ecosystem is unaffected by climactic events?
A = The null hypothesis is rejected since there are significant effects of EAWM and PDO on surface sea temperature and copepod abundance: The null hypothesis should be rejected because the data indicate that the EAWM and the PDO have significant effects on surface sea temperature as well as copepod abundance.
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Researchers were studying the effects of microbes on the growth of the yellow bedstraw plant, Galium verum. They grew yellow bedstraw plants under four treatments: in the presence of soil bacteria only, arbuscular mycorrhizal (AM) fungi only, both bacteria and AM fungi, or neither. After 6 months, they measured the biomass of the plants (Figure 1). Figure 1. The Effect of Soil Microbes on the Biomass of Galium verum Which of the following best describes a statistically significant relationship indicated in Figure 1 ?
A = Yellow bedstraw plants grow significantly more in the presence of both soil bacteria and AM fungi (treatment 4) than in the presence of soil bacteria alone (treatment 2): The error bars in treatments 2 and 4 do not overlap, which means that the differences between the two data sets are statistically significant. Thus, AM fungi significantly increases yellow bedstraw growth when these plants are exposed to soil bacteria.
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Students in a class were divided into five groups to analyze community structure. Each group of students assessed the species of plants in four environments and determined the Simpson's Diversity Index for each environment. The Simpson's Diversity Index takes into account the number of species present as well as the abundance of each species. The index values are shown in Figure 1. Figure 1. Simpson's Diversity Index for four environments Based on the data in Figure 1, which of the following statements is most accurate about the species diversity of the four different environments that the students analyzed?
C = Based on the data, there is no statistically significant difference between the species diversity of plants in the light, moist environment and in the dark, moist environment: Because the error bars overlap, the light, moist and dark, moist environments show no significant statistical difference in diversity.
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In a study of energy flow, the following data were collected: Each human requires 55 grams of protein per day. An acre of soybeans produces 200,000 grams of protein per year. A cow grazing on one acre of land produces 19,000 grams of protein per year. Based on these data, an acre of land would support: 10 humans per year on a diet of soy, or 0.9 human per year on a diet of beef. Which of the following statements best explains these relationships in terms of energy transfer?
D = Only 10% of the energy on each level of the trophic pyramid is available for use by the next level. The rest is lost as heat or used for growth and repair: The 10% rule states that approximately 90% of the energy at any trophic level is lost to heat, growth, and repair of the organisms, and only 10% is available for harvesting by the next trophic level.
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The marine iguana, Amblyrhynchus cristatus, is endemic to the GalÃ¡pagos Islands and is especially vulnerable to El NiÃ±o events. These iguanas feed on red and green algae. During an El NiÃ±o climate event, surface waters and their currents in the central and eastern Pacific Ocean become significantly warmer than usual. Also during El NiÃ±o years, land masses experience increased rainfall. A researcher suggests that El NiÃ±o conditions cause a significant decrease in the size of the GalÃ¡pagos marine iguana population. Which of the following would best support this alternative hypothesis?
B = Warm surface water contains fewer nutrients needed by red and green algae than cooler surface waters does: Upwelling brings cold, nutrient-rich waters to the surface. During El NiÃ±o years this is inhibited, so algae populations decrease because nutrients are limiting, resulting in decreased marine iguana populations.
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A study recorded changes in the distribution of some commercial marine species off the East Coast of the United States over a period of several decades. The results of the study are summarized in Figure 1. Figure 1. Latitude that is the center of commercial harvesting of specified marine species Some researchers link changes in the distribution of these species to warming of the oceans due to climate change. Which of the following pieces of data best supports this alternative hypothesis?
C = The prey of these species require colder waters to survive, and owing to warming in the oceans, they are moving farther north, to higher latitudes, where the water is colder: Global increases in average temperature are associated with global climate change. This would produce warming in the oceans, so the prey these fish depend on can survive only by moving to more northern latitudes with colder waters. The fish would move with their food sources.
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Sea otters living along the Pacific coast were hunted to near extinction in the nineteenth century. After being protected from hunting in the early 1900s, a remnant population of otters near Adak Island, Alaska, recovered rapidly. Otters did not return to the environmentally similar nearby island, Alaid Island. Sea otters eat sea urchins, which eat kelp, a brown alga. Researchers surveyed both islands in 1988, to measure sea urchin biomass and kelp density. The data are presented in Table 1. In 1991, researchers at Adak Island observed the first attack by a killer whale on a sea otter in historical times. The researchers hypothesized that the population sizes of the larger marine mammals that the killer whales normally prey on declined, so the killer whales were starting to prey on different prey, including the smaller sea otters. Which of the following best predicts the effects of an increase in killer whale predation on sea otters on the Adak Island ecosystem?