Unit 5 Population Dynamics Answers to Unit Preparation Questions Assessing Student Readiness (Student textbook pages 492–5) PDF

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A population is a group of organisms of one species that lives in the same place, at the same time, and can successfully reproduce, but a community refers to the populations of all the species that interact in a certain area....

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Answer Key Unit 5 Population Dynamics

d. grasshopper e. energy

Answers to Unit Preparation Questions Assessing Student Readiness

f. four

(Student textbook pages 492–5) 1. A population is a group of organisms of one species that lives in the same place, at the same time, and can successfully reproduce, but a community refers to the populations of all the species that interact in a certain area. 2. e 3. Both ecosystems are aquatic. The main difference between the two ecosystems is that eels hatch, spawn and die in an ocean-based saltwater environment but live much of their lives an inland freshwater environment. Each of these environments has different water conditions and provides different food sources. 4. a. True b. False, carnivorous plants would not do well in conditions to which they are not well-adapted. c. False, two or more species cannot occupy the same ecological niche.

13. Decomposers would appear at each trophic level as they would extract energy from each organism when it dies. 14. a. No, because it is commonly accepted that less than 10% of available energy is transferred from one trophic level to the next. b. Each organism uses much of the energy it consumes for its biological processes and some energy is transferred to the environment in the form of heat. 15. On average, only about 10 percent of the energy available at one trophic level is available to consumers at the next trophic level. Animals that make up the highest trophic level in any food web tend to be large, predatory species such as bears, lions, whales, and eagles. Since there is less biomass (and therefore less energy) from lower to higher trophic levels, there can only be a few of these large animals in any ecosystem compared with much larger numbers of organisms such as deer at lower trophic levels, where biomass and food energy is more plentiful.

5. d

16. Webs should include producers and a number of primary, secondary, and tertiary consumers, linked appropriately. 6. a. Amount of sunlight, temperature range, and amount of precipitation. a. Freshwater lakes contain many omnivorous species. Producers might include algae, (some) bacteria, b. Predatory insects, organisms that cause disease or diatoms, and Daphnia. Primary consumers that are parasitic, and competition for nutrients, might include zooplankton and larvae of fish or space, and sunlight. amphibians. Secondary consumers might include 7. Each type of fish is a separate population in Lake insects, small fish, and frogs. Tertiary consumers Superior. Together, all of the fish make a community. might include large fish, predatory birds, and 8. c humans. Each level should be linked to decomposers (i.e., certain bacteria). 9. b b. Forest webs should include distinct herbivores 10. Sample caption: Fungi absorb nutrients from dead and carnivores/omnivores. Producers might organisms on the forest floor. include grasses, shrubs, trees, and wildflowers. 11. If a keystone species is removed from an ecosystem, Primary consumers might include forest herbivores the ecosystem is harmed because the food web is such as bears, moose, deer, elk, rabbits, insects disrupted. The balance in the ecosystem no longer (grasshoppers), birds (seed eaters), small rodents exists and the ecosystem can collapse. (e.g., squirrels, chipmunks), and beaver. Secondary 12. a. The hawk is a predator and the frog is the prey. consumers might include insect- and rodent-eating b. bunchgrass birds (e.g., flycatchers, owls, hawks), weasels, foxes, and raccoons. Tertiary consumers might include c. spotted frog

Biology 12 Answer Key Unit 5 • MHR TR

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large predators such as wolves, lynx, and forest cats. Each level should be linked to decomposers (i.e., certain bacteria and fungi). c. Prairie food webs should include distinct herbivores and carnivores/omnivores. Producers might include grain crops, grasses, and wildflowers. Primary consumers might include insects (e.g., grasshoppers), rabbits, bison, and cattle. Secondary consumers might include frogs, coyotes, birds (e.g., meadowlarks, prairie chickens), skunks, snakes, mice, and shrews. Tertiary consumers might include birds of prey (e.g., hawks, eagles). 17. Background extinction occurs at a fairly steady rate over a long period of time and generally involves a limited number of species at a given time. A mass extinction, on the other hand, occurs when there is a sudden change to Earth’s ecosystems and many species die out in a relatively short period of time. 18. a. Wetlands are home for a great number and variety of plants and animals. They promote biodiversity through their habitat, providing a protected environment in which juvenile organisms grow and mature, and in which migrating birds feed and rest, allowing them to spread farther afield. b. Humans destroy wetlands with pollution and by draining them to create farmland, put up buildings, and control mosquitoes. 19. Both species may be introduced from another area. An invasive species is an alien species that out-competes (takes over) habitat of a native species.

25. Remembering that evolution involves changes in allele frequencies at the population level from one generation to the next helps set a timeline. An individual may exhibit traits that differ slightly from the rest of the population, but this does not indicate that evolution has occurred. Evolutionary change occurs in percentages, or frequencies, of alleles within populations over generations. 26. d 27. Sample answer: A selection factor changed, for example, predation decreased or the availability of food increased. 28. b 29. a 30. a. 1960 to about 1963 b. No, growth will eventually slow as the population reaches the carrying capacity of its environment. 31. d 32. a. A is a point of moderate or steady growth and B represents the carrying capacity. b. The population grew because seal hunting was reduced. c. The population did not change after 1935. It had reached the carrying capacity of the environment. d. Limiting factors could include: food, habitat, available mates, predators, disease. 33. c

34. Population growth occurs when there are no factors that limit growth (limiting factors). The population 20. Sample answer: Overexploitation means excessive reaches the carrying capacity of the environment when harvesting of a species, for example, bison, elephants, limiting factors restrict further population growth. or cod, such that the species is no longer able to sustain its populations. The species can become endangered or it can become locally extinct (i.e., extirpated). Not Chapter 11 Describing only will the overexploited animal disappear from the ecosystem, but all other organisms that depend on the Populations and Their Growth extinct species for food or other resources could have difficulty surviving. In addition, if the extinct species is Answers to Learning Check Questions a predator, its disappearance could trigger a population (Student textbook page 505) explosion of prey species and further unbalance the 1. It is impractical to count individuals in ever-changing ecosystem and threaten biodiversity. populations because of time, money, and human resources; therefore, ecologists estimate populations. 21. e 22. e 23. a 24. a. a structural adaptation b. Predators mistake it for part of the branch so it avoids being eaten.

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MHR TR • Biology 12 Answer Key Unit 5

2. Biologists sample subsets of populations using transects, quadrats, and mark-recapture techniques, and then estimate (or extrapolate) to the larger population to estimate the size.

3. In the mark-recapture method, animals are caught, tagged, and released. Then, another set is caught at a later date. The proportion in that set of previouslytagged animals to unmarked animals is used to estimate population size. 4. Aspens have clumped distribution because they can reproduce asexually, sprouting new plants from shoots that grow off their root system. In addition, the trees tend to cluster in areas where soil, moisture, and temperature conditions are optimal for growth.

14. Intraspecific competition for resources occurs among members of the same population, while interspecific competition occurs between two or more populations. 15. The more successful predators thrive, so the traits that make them successful will be passed on. Prey that survive will also pass on any trails that helped them survive. Traits that made prey more susceptible to predation, or that made predators less successful, will be eliminated from the population.

16. As predators feed on prey, the predator population increases and the prey population declines. This leads 5. Populations often exhibit a clumped distribution pattern when resources are unevenly distributed. When to competition among predators for food, causing the populations show a uniform distribution pattern, predator population to decline. With fewer predators, resources tend to be evenly distributed but scarce. the prey population then increases, resulting in a cycle. Resources are usually plentiful and evenly distributed 17. There is generally a “ripple effect” in which other when population distribution is random. populations grow or decline because of reduced 6. The interactions are positive because they tend to benefit the population. For many species in clumped distributions, interactions give protection from predators, promote hunting efficiency, and allow collective raising of the young.

(Student textbook page 513) 7. Birth, death, immigration, and emigration; ∆N = (B + I) - (D + E) 8. In most populations, immigration and emigration are about equal. 9. In order to make sound decisions about managing and protecting species and the environment 10. The growth rate is the change in population size over the specified time period (3 years): Change in population size: 3600 - 1500 = 2100 Growth rate = 2100/3 = 700 The growth rate is 700 geese per year. 11. Population A shows a greater increase than population B because population A was greater at the start. To make a more meaningful comparison, use the per capita growth rate. 12. A negative per capita growth rate means that the size of the population is declining over time. These changes are likely because deaths outnumber births or emigration exceeds immigration, or both.

(Student textbook page 529) 13. Abiotic factors generally cause a sharp drop in population growth before the habitat reaches carrying capacity. On the other hand, biotic factors slow the growth of the population when it becomes dense.

competition, predation, or resources. 18. Camouflage protects the butterfly from predators since it appears to be a dead leaf.

Answers to Caption Questions Figure 11.1 (Student textbook page 498): It is difficult to count every individual in a very large population such as this forest. Counting each individual is limited by human ability, time and money. Figure 11.5 (Student textbook page 501): The bald eagle benefits from a uniform distribution pattern because it maintains sole access (or nearly) to the limited resources in its territory. The moose benefits from a random distribution pattern because it can move freely to use the abundant resources without the need to defend or share resources. The aspen benefits from a clumped distribution pattern because its population grows where conditions are optimal for survival. Figure 11.13 (Student textbook page 511): The species may become extinct. Figure 11.14 (Student textbook page 512): The population size of A was five times the population of B at the start. Since there were more individuals to reproduce in population A its doubling resulted in faster growth. Figure 11.19 (Student textbook page 517): Spring hatching means that young will experience milder weather and abundant food. Figure 11.22 (Student textbook page 520): While ice covered everything, access to some food and habitat was eliminated. Damage to trees reduced habitat and resources. Figure 11.24 (Student textbook page 521): Parasites pass from one host to another, a process that is supported by a high density of hosts.

Biology 12 Answer Key Unit 5 • MHR TR

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Figure 11.28 (Student textbook page 523): Organisms with adaptations suited to different ecological niches do not compete with each other even if they are living within the same small area. This assists in each organism satisfying its needs for survival and increases the chance that each will survive.

Uniform Distribution

9.

Random Distribution

Figure 11.32 (Student textbook page 526): The survival of the hares would be affected by abiotic factors such as extreme weather, the availability of abundant clean water, or by biotic factors such as disease.

Answers to Section 11.1 Review Questions (Student textbook page 508) 1. Population size, density, distribution, and life history 2. Small sample areas are counted and extrapolated to the entire area. 3. 0.14 flowering dogwood per square metre, population about 7000 4. Relative densities of deer and coyote populations 5. The information should lead to an estimate of 16 Blanding turtles living in the marsh. The markrecapture method the biologist used is best for populations that are highly mobile. Since a turtle is not highly mobile, A transect is useful for low density populations (like endangered species), but since Blandings live in marshy areas, the mark-recapture method is most suitable. 6. The life history of populations is the key factor contributing to estimated population density, specifically, fecundity (the average number of offspring per female) and survivorship (the percentage of organisms that live long enough to reproduce).

Clumped Distribution

10. During the rainy season, vegetation (food) is uniform and abundant, so the distribution of the cattle is random. See the random distribution model in Figure 14.5 on page 469 of the student textbook. During the dry season, vegetation may be clumped and varied, so the distribution of the cattle is clustered near available vegetation. See the clustered distribution model in Figure 14.5 on page 469 of the student textbook. 11. Wolves travel in packs, a clumped distribution pattern, to increase efficiency in hunting and for protection. They are territorial, with packs being uniformly distributed to defend their food, shelter, and mating habits. 12. Humans have the highest fecundity during late adolescence/young adulthood when females are best able to reproduce. 13. The greater the number of offspring, the less energy is invested into taking care of them, because the mother cannot feed or protect so many of them for very long.

7. Sample table: Survivorship Pattern Type I

Number of offspring at one time high

Age at sexual maturity young

Energy output (prenatal care) low

Survival rate of young individuals low

Type II

medium

middle

medium

medium

Type III

low

older

high

high

8. Sample answer: Large-mouth bass are found in a part of a lake that provides optimal resources for its survival. Crude density would describe the number of large-mouth bass per total area of the lake, while ecological density would describe the number of large-mouth bass per area of the lake used by largemouth bass.

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MHR TR • Biology 12 Answer Key Unit 5

number of eggs, which will have little parental care. A large number of the offspring will die soon after hatching or as tadpoles. Only a small percentage will reach sexual maturity to reproduce.

Answers to Section 11.2 Review Questions (Student textbook page 519) 1. A value of zero can be assigned to the growth rate of a stable population if birth and death rates are equal.

10. Populations with r-selected life strategies reproduce at an early age and have many offspring. Since they take advantage of favourable environmental conditions, such as sunlight and warm temperatures to live close to their biotic potential, the term opportunistic population is suitable.

2. Birth rate increases the per capita growth rate, since birth rate reflects the rate at which new members enter 11. The exponential growth (J-shaped curve) represents the population. the insect. There is a brief lag phase when the 600 - 800 -200 population is small, followed by an exponential 3. Per capita growth rate = = = -4%. 5000 5000 growth phase when the population is displaying its The per capita growth rate of the population is -4% biotic potential. The logistic growth (S-shaped curve) 4. Design a study to examine populations by country. represents the mammal. There is a lag phase of slow Gather data about the population, births, deaths, growth when the population is small, followed by a immigration, and emigration over a certain period, rapid growth phase due to its biotic potential, and such as 10 years. Then, determine the per capita then growth slows as resources become limited and growth rate to compare them. Or, plot population size individuals compete for resources, finally leading to no versus time on the same graph and analyze the slope to growth (where birth rate and death rate are about the determine the rate of change of the populations. same); therefore, it reaches its carrying capacity. 5. Exponential growth does not last long in nature since there are environmental limits to the growth of any population. As a population grows, it impacts the resources, and therefore death rate increases while birth rate decreases. 6. Zero, because the birth rate and death rate are about the same. 7. A population does not grow to its biotic potential when resources become limited. As individuals spend energy competing for resources, growth slows. The resulting curve for the researchers’ data should be S-shaped (logistic growth pattern). If the researcher tries to control the environment to make it “ideal,” the population will likely live near its biotic potential and the researcher’s data will show a J-shaped curve (exponential growth pattern). 8. Graphs should show a population that increased exponentially (a steep curve up), followed by a population crash (a steep curve down). The conditions in the field were ideal for the weeds, so a few weeds released many seeds which quickly matured and released their own seeds. The population increased exponentially, as the population was growing at its biotic potential; thereby creating a population explosion. When the herbicide was used, it created an unfavourable environment, killing the weeds before the habitat reached carrying capacity; causing a population crash. 9. Consider life span, age of sexual maturity, number of offspring in a reproductive cycle, and amount of parental care of each species.

12. Diagrams should resemble the red line in the graph from question 11. Figure 11.18 on page 516 of the student textbook, without the red line which shows exponential growth. 13. Such populations require a stable environment and generally live close to carrying capacity. They are generally slower to mature and produce few offspring, which need to be cared for. When humans disrupt their environment to build or farm, for instance, the balance in their way of life is interrupted or destroyed. Since they do not adapt well to major change, this puts the populations at risk. 14. The number of offspring per reproductive cycle and the number that survive long enough to reproduce, the age of reproductive maturity, the number of times individuals reproduce in a lifetime, and the life span of individuals.

Answers to Section 11.3 Review Questions (Student textbook page 533) 1. Density-independent and density-dependent factors both influence population size. Density-independent factors, such as weather and natural disasters, do not depend on the density or size of the population. For example, cold weather may kill a population of insects. But, density-dependent factors such as competition depen...