Lesson 6 – Population ecology
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1. A uniform dispersion pattern for a population may indicate that
a. the population is spreading out and increasing its range.
b. resources are heterogeneously distributed.
c. individuals of the population are competing for some resource, such as water and minerals for
plants or nesting sites for animals.
d. there is an absence of strong attractions or repulsions among individuals.
e. the density of the population is low.
2. A "cohort" in a human life table consists of
a. people who are the same age.
b. people who live in the same city.
c. people of the same education level.
d. people who have the same occupation.
e. people who have the same number of children.
3. The term (K—N)/K influences dN/dt such that
a. the increase in actual population numbers is greatest when N is snall.
b. as N approaches K, r, the intrinsic rate of increase, becomes smaller.
c. when N equals K, population growth is zero.
d. When K is small, the population begins growing exponentially.
e. as N approaches K, the birth rate approaches zero.
4. A population's carrying capacity I
a. the number of individuals in that population.
b. a constant that can be estimated for all populations.
c. inversely related to r.
d. the population size that can be supported by available resources for that species within the
e. set at 8 billion for the human population.
5. Which life history strategy would be favored by natural selection if survival of offspring is quite low and unpredictable?
a. big-bang reproduction, or semelparity.
b. production of a large number of large eggs and a great deal of parental care.
c. repeated reproduction, or iteroparity.
d. very early age of first reproduction.
e. relatively late age of first reproduction.
6. In a mark-recapture study of a lake trout population, 40 fish were ceptured, marked, and released. In a second capture, 45 fish were captured; 9 of these were marked. What is the estimated number of individuals in the lake trout population?
7. The current size of the human population is closest to
a. 2 million.
b. 3 billion.
c. 4 billion.
d. 6 billion.
e. 10 billion.
8. All these descriptions are characteristic of human populations in industrialized countries except
a. relatively small family size.
b. several potential reproductions per lifetime.
c. r-selected life history.
d. Tpe 1 survivorship curve.
e. relatively even age structure.
9. According to the study of ecological footprints produced in 1997,
a. the carrying capacity of the world is 10 billion.
b. the carrying capacity of the world would be higher if all people became vegetarians.
c. the current demand on global resources by each industrialized country is well below the
ecological capacity of those countries.
d. the United States has a larger ecological footprint than available ecological capacity of its own
e. a technological fix to expand the world's carrying capacity is not ecologically sound.
10. When a biologist studies the way organisms interact with each other and with their environment, she is studying their
11. In a deciduous oak forest of the American northeast, one example of an abiotic component of the ecosystem would be
a. nematodes in the soil that feed on plant roots
b. nematodes in the soil that feed on dead organic matter
c. sunlight that filters through the canopy
d. animals such as deer that migrate through the forest but do not eat in the forest
e. the understory plant community
12. A complex interrelated network of organisms and the surrounding abiotic environment in a defined area is a(n):
13. All organisms that reside within an ecosystem and that can potentially interbreed are members of a(n)
c. trophic level
14. The organisms that represent the different species within an ecosystem that interact in various ways comprise the
c. trophic level
15. Environmental resistance may limit the size of populations by
a. increasing both birth and death rates
b. decreasing both birth and death rates
c. increasing death rates and/or decreasing birth rates
d. decreasing death rates and/or increasing birth rates
e. changing the biotic potential
16. To determine the number of individuals that will be added to a population in a specified time we multiply the growth rate (r) by the ________.
a. biotic potential
b. original population size
c. environmental resistance
d. final population size
e. number of immigrants
17. If a population of 100 birds increases to 120 birds the following year, r = ___________.
18. Which factor would not influence the size a population reaches over time?
a. Number of individuals migrating
b. Number of deaths
c. Age of females at reproduction
d. Distance travelled by migrants
e. Number of births
19. Environmental resistance
a. is limits imposed on population growth by the biotic environment (predators, competitors)
b. is limits imposed on population growth by the abiotic environment
c. is limits imposed on population growth by both the biotic and abiotic environment
d. is a factor that decreases both death rates and birth rates
e. is a factor that increases both death rates and birth rates
20. The biotic potential of a population
a. directly affects environmental resistance
b. causes changes in birth rates without affecting death rates
c. causes changes in death rates without affecting birth rates
d. is the maximum rate at which a population may increase
e. both a and c
21. There are 150 spotted owls in an old-growth forest patch in western Oregon. A biologist tracking the birds saw that in one year, 25 new birds were hatched, and 5 died. Thus r =
22. Exponential growth occurs when
a. there is a constant number of births each year and b > d
b. the population grows by a fixed percentage each year
c. immigration is greater than emigration
d. the biotic potential increases each year
e. environmental resistance declines each year
23. When a population has inhabited an area for a long time and the population size has stabilized because of resource limitations:
a. Carrying capacity has been reached
b. Density dependence occurs
c. Predation decreases
d. Density independence occurs
e. Environmental resistance declines
24. An insect population grows exponentially until an early winter freeze kills almost all of the insects. The next spring the population grows exponentially again. This type of population growth is known as
a. Boom and bust
25. The human population is currently following a J-shaped curve. This means that the population is growing
c. At a decreasing rate
d. By a boom and bust cycle
26. An important density-independent factor limiting population size is __________.
c. Environmental resistance
e. Food quantity
27. Which of these is not a density-dependent control of population size?
d. Biotic potential
e. Shortage of food
28. Density-dependent factors such as predation have _________________ effect on population size.
a. a long-term
b. a short-term
c. a negative feedback
d. a positive feedback
29. If a caterpillar eats a seedling in your garden, the caterpillar is acting as a
d. Density-independent factor
30. Predators and parasites are always harmful to their prey or host populations.
b. False, because predators always harm the prey population, but parasites often do little
or no harm.
c. False, because parasites always harm their host populations but predators may be helpful.
d. False, because parasites and predators kill their hosts and prey.
e. False, because predators and parasites often help the host or prey population by attacking
31. In a maple forest in the spring the ground will often be covered with young maple seedlings which compete for light and nutrients. By fall, most of these have died, leaving only a few survivors. This is an example of ____________ competition.
c. dominance hierarchy
e. social stress
32. Most parasites have evolved to _________ their host.
b. only weaken
c. have no effect on
e. all of these
33. What type of competition has occurred when one organism uses social or chemical interactions to limit the access of other individuals to resources?
a. Contest competition
b. Scramble competition
34. A caribou dies because it was weakened by parasites (like tapeworms) passed from one individual to the next under crowded conditions during an unusually long, cold winter. What killed the caribou?
a. Density-independent factors
b. Density-dependent factors
c. Abiotic factors
d. Biotic factors
e. Both density-dependent and density-independent factors
35. Some predators feed preferentially on the most abundant prey. This type of predation is:
a. Density dependent
b. Density independent
36. Why do many non-native species, such as a prickly pear cactus brought to Australia from South America, rapidly become abundant when first introduced?
a. The climate in the new site is more favorable than it's native site
b. Non-native species increase their reproductive rate when introduced
c. There are fewer predators and parasites capable of attacking the non-native species in the
d. The carrying capacity at the new site is higher than at the native site
e. Growth changes from an S-curve to a J-curve at the new site
37. An ecosystem's carrying capacity for a population is determined by all of the following factors except:
38. The carrying capacity of an ecosystem is determined by
a. the number of ecotones in the ecosystem
b. the availability of resources in the environment
c. demand for space
d. demand for space, water and light
e. the intersection between environmental resistance and biotic potential
39. Parasites affect population sizes of their hosts
a. in a density dependent fashion, and usually directly kill the hosts
b. in a density dependent fashion, and do not usually directly kill the hosts
c. in a density independent fashion, and usually directly kill the hosts
d. in a density independent fashion, and do not usually directly kill the hosts
e. in a density dependent fashion, and do not affect host death rates
40. Juglans nigra, or the black walnut, releases an allelopathic (toxic to other plants) compound when its leaves decompose; the result is that few plants can live under the canopy of the tree. Thus the black walnut can be said to engage in
b. scramble competition
c. sociopathic competition
d. allele-dependent competition
e. contest competition
41. The distribution pattern associated with organisms that are grouped together because of availability of resources, for mating, or for protection from predators is
42. Cottonwood trees grow in groups only along streams and rivers in grasslands. This is an example of what kind of distribution?
43. Some desert plants (such as the creosote bush) secrete chemicals which inhibit the growth of nearby plants. This results in ________ distribution.
44. When organisms (rainforest plants, for example) form no social groups and the resources they need are evenly distributed, they will often show _________ distribution.
45. Species which are territorial, such as nesting Redwing Blackbirds, often show a/an _________ distribution pattern.
46. If most of the individuals of a species die when they are young, that species will exhibit a ________ survivorship curve.
d. sigmoid (S-shaped)
47. If the individuals of a species are very likely to live until old age, that species will exhibit a ________ survivorship curve.
d. sigmoid (S-shaped)
48. If all the individuals of a species have an equal chance of dying at any age, that species will exhibit a ________ survivorship curve.
d. sigmoid (S-shaped)
49. Which survivorship curve is characteristic of many large animals including humans?
a. Early loss
c. Constant loss
d. Late loss
50. Human populations have continued to grow because humans have increased the ____________ of the earth by agriculture, medicine, and technology.
a. biotic potential
b. evolutionary pressure
c. environmental resistance
e. carrying capacity
51. In the 18th and 19th centuries people increased the capacity of the earth to support more humans by the discoveries of the _____________ revolution.
52. At current rates of growth there will be about ____ million more people on the earth a year from now than there are today.
53. Which best describes the reason for the very rapid growth of the human population in the last 8,000 years?
a. Humans have a late-loss survivorship curve.
b. Environmental resistance does not apply to humans.
c. Climatic change has allowed the human species to expand its range.
d. Technology has allowed the species to overcome some environmental resistance.
e. The biotic potential for humans has increased.
54. Population growth rates are high in less-developed countries because
a. Medicines have lowered death rates.
b. Wealth has not lowered birth rates.
c. Children are often an important economic advantage.
d. Social traditions support large families.
e. All of these are important reasons why population growth is high in less-developed countries.
55. In areas with a stable population, the number of children is
c. Approximately equal to the number of adults
d. Higher than the number of adults
e. Lower than the number of adults
56. In countries such as Nigeria which have large numbers of children under age 15, the population is
a. Becoming larger
b. Becoming smaller
c. Staying the same
d. Hard to predict
e. Able to expand their carrying capacity
57. If a population's age structure diagram looks like a pyramid, the:
a. Population is expanding
b. Population is remaining the same
c. Population will expand for at least a generation
d. Population is showing continuous exponential growth
58. In countries such as France in which the number of children below 15 is approximately equal to the number between 15 and 45, the population is
a. Expanding slowly
c. Shrinking slightly
d. Growing exponentially
e. Declining drastically
59. Less-developed countries tend to have a(n) ________________ age diagram.
b. inverted triangle
60. If people in less-developed countries reached replacement-level fertility immediately, their populations would
a. Decline slowly.
b. Decline rapidly.
c. Become stable.
d. Continue to grow for many years.
e. Grow for a short time and then decline rapidly.
61. The population of the USA continues to grow as a result of
b. Babies born to baby boom generation parents
c. Increases in fertility
d. The birth rate was above replacement level fertility during the 1940's through 1960's
e. All of the above are causes of population growth in the USA
62. The United Nations estimates that by 2150 the world's population may stabilize at about ______ billion.
63. If all people in the world were to live at the level which Americans live in terms of technology, wealth, education, etc., the population of the world would have to ___________________ in order to support them.
b. reduce by half
c. reduce to a fourth of current levels
d. reduce to less than a 10th of the current population
e. decline by 90%
64. At present, the earth's human population is:
c. Increasing exponentially
d. Increasing at a constant rate
e. Increasing at about 10% per year
65. A population grows exponentially when:
a. the birth rate and the death rate are equal
b. the birth rate exceeds the death rate and there is no immigration or emigration
c. emigration exceeds immigration and the birth rate equals the death rate
d. the birth rate equals the death rate and immigration is equal to emigration
e. the carrying capacity is exceeded
66. An aquatic biologist is studying a lake in western Massachusetts in order to document the N cycle of the lake, and thus she is measuring inputs, turnover, and outputs of N. A second ecologist is studying a larger region of western Massachusetts that is forested, with several lakes, and is studying N transfers between the forest and the lakes. The first ecologist claims that her lake is an ecosystem; the second ecologist also claims that her forested region, with its many lakes, is an ecosystem. Which ecologist is correct, or are they both wrong or right?
67. Bacteria growing in a petri dish may grow rapidly and experience exponential growth. However, bacteria in the soil, measured as the number of organisms per gram of soil, usually do not increase in population size from one year to the next. Yet no new food is added to the petri dish after the initial addition of the bacterial innoculum, but new food sources are always added to the soil by way of plant detritus. How can this be true?
68. Although models of population structure in an ecosystem usually assume that populations reach a carrying capacity after time, in fact, population size may fluctuate around a mean from year to year. Using a population of mice in a grassland, give (1) an example of a density-independent factor that could cause population size to increase; (2) an example of a density-independent factor that could cause population size to decrease; (3) an example of a density-dependent factor that could cause population size to increase; (4) an example of a density-dependent factor that could cause population size to decrease.
69. Write an equation which describes a situation in which a population remains stable.
70. Explain what happens in exponential population growth.
71. In the United States today there is a trend toward women having their first child in their late 30's or early 40's. By contrast, a few years ago most women started having children in their early 20's. What effect would you expect this change to have on population growth in the USA? Would it have any effect if the number of children per woman is the same? Explain.
72. Why would a bacterial population living in an unrestricted environment grow much faster than an eagle population?
73. Predation is considered to be a density dependent factor that controls the population size of prey species. Give two examples of ways in which predators act in density dependent ways in response to fluctuations in prey population sizes.
74. Parasites may often kill their hosts, although they do not directly benefit from host death. And yet, many ecologists believe that parasites may have beneficial effects on their host populations. Why might this be so?
75. In high elevation forested ecosystems of New Hampshire and Vermont, ecologists have noticed a serious decline in certain tree species such as red spruce. When the affected trees are studied, it often seems that parasitic beetles or microbes are involved. Other scientists have stated that acid rain might be the cause of red spruce decline. Yet a third group of scientists have argued that both factors are equally involved. How could this third possibility be true, and which cause is likely to be density dependent, and which is more likely to be density independent?
76. How do interspecific and intraspecific competition differ from each other?
77. Which tends to be more intense, intra or interspecific competition? Explain why.
78. Animal species often show a clumped spatial pattern due to mating or cooperation; uniform patterns might arise from a competition for resources such as nesting space. Desert plants such as the perennial shrub Larrae tridentata often show uniform spatial patterns in extremely dry desert conditions, and random spatial patterns in more mesic deserts. Why might this be so?
79. Just after the Industrial Revolution, many countries in Europe saw expanding populations: infant mortality went down and family size increased. However, after World War II, many countries in Eastern Europe are actually declining in population as families choose to have either one or no children. Draw the 2 age-structure diagrams for a country such as Hungary, with first the post-Industrial Revolution scenario, and then the current scenario. Hint: number of individuals by age is represented on the x-axis, and age is represented on the y-axis.
80. The U.S. fertility rate in 1999 was 2.1 meaning that the average family had 2.1 offspring. Why is 2.1 considered to be replacement level fertility in developed countries, and not 2? Finally, if the U.S. has replacement level fertility, why is the population growing rapidly?
81. What are the 3 shapes of survivorship curves, and what does each one tell about the population?