Answer Key
Unit 5 Population Dynamics
Answers to Unit Preparation Questions
Assessing Student Readiness
(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.
5. d
6. a. Amount of sunlight, temperature range, and amount
of precipitation.
b. Predatory insects, organisms that cause disease or
that are parasitic, and competition for nutrients,
space, and sunlight.
7. Each type of fish is a separate population in Lake
Superior. Together, all of the fish make a community.
8. c
9. b
10. Sample caption: Fungi absorb nutrients from dead
organisms on the forest floor.
11. If a keystone species is removed from an ecosystem,
the ecosystem is harmed because the food web is
disrupted. The balance in the ecosystem no longer
exists and the ecosystem can collapse.
12. a. The hawk is a predator and the frog is the prey.
b. bunchgrass
c. spotted frog
d. grasshopper
e. energy
f. four
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.
16. Webs should include producers and a number of primary,
secondary, and tertiary consumers, linked appropriately.
a. Freshwater lakes contain many omnivorous species.
Producers might include algae, (some) bacteria,
diatoms, and Daphnia. Primary consumers
might include zooplankton and larvae of fish or
amphibians. Secondary consumers might include
insects, small fish, and frogs. Tertiary consumers
might include large fish, predatory birds, and
humans. Each level should be linked to decomposers
(i.e., certain bacteria).
b. Forest webs should include distinct herbivores
and carnivores/omnivores. Producers might
include grasses, shrubs, trees, and wildflowers.
Primary consumers might include forest herbivores
such as bears, moose, deer, elk, rabbits, insects
(grasshoppers), birds (seed eaters), small rodents
(e.g., squirrels, chipmunks), and beaver. Secondary
consumers might include insect- and rodent-eating
birds (e.g., flycatchers, owls, hawks), weasels, foxes,
and raccoons. Tertiary consumers might include
Biology 12 Answer Key Unit 5 • MHR TR
1
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.
20. Sample answer: Overexploitation means excessive
harvesting of a species, for example, bison, elephants,
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
only will the overexploited animal disappear from the
ecosystem, but all other organisms that depend on the
extinct species for food or other resources could have
difficulty surviving. In addition, if the extinct species is
a predator, its disappearance could trigger a population
explosion of prey species and further unbalance the
ecosystem and threaten biodiversity.
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.
2
MHR TR • Biology 12 Answer Key Unit 5
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
reaches the carrying capacity of the environment when
limiting factors restrict further population growth.
Chapter 11 Describing
Populations and Their Growth
Answers to Learning Check Questions
(Student textbook page 505)
1. It is impractical to count individuals in ever-changing
populations because of time, money, and human
resources; therefore, ecologists estimate populations.
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.
5. Populations often exhibit a clumped distribution
pattern when resources are unevenly distributed. When
populations show a uniform distribution pattern,
resources tend to be evenly distributed but scarce.
Resources are usually plentiful and evenly distributed
when population distribution is random.
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.
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
to competition among predators for food, causing the
predator population to decline. With fewer predators,
the prey population then increases, resulting in a cycle.
17. There is generally a “ripple effect” in which other
populations grow or decline because of reduced
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
3
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.
9.
Uniform Distribution
• scarce
resources
• uniform
resource
distribution
• negative
interactions
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.
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).
7. Sample table:
Age at sexual
maturity
• varied abundance of
resources
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.
Energy output
(prenatal care)
Survival rate
of young
individuals
Type I
high
young
low
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.
4
MHR TR • Biology 12 Answer Key Unit 5
• neutral
interactions
• positive interactions
(Student textbook page 508)
1. Population size, density, distribution, and life history
Number of
offspring at
one time
• abundant
resources
• clumped resources
Answers to Section 11.1 Review Questions
Survivorship
Pattern
Random Distribution
14. The frog should have high fecundity, producing a large
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.
2. Birth rate increases the per capita growth rate, since
birth rate reflects the rate at which new members enter
the population.
600 - 800 -200
=
= -4%.
3. Per capita growth rate =
5000
5000
The per capita growth rate of the population is -4%
4. Design a study to examine populations by country.
Gather data about the population, births, deaths,
immigration, and emigration over a certain period,
such as 10 years. Then, determine the per capita
growth rate to compare them. Or, plot population size
versus time on the same graph and analyze the slope to
determine the rate of change of the populations.
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.
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.
11. The exponential growth (J-shaped curve) represents
the insect. There is a brief lag phase when the
population is small, followed by an exponential
growth phase when the population is displaying its
biotic potential. The logistic growth (S-shaped curve)
represents the mammal. There is a lag phase of slow
growth when the population is small, followed by a
rapid growth phase due to its biotic potential, and
then growth slows as resources become limited and
individuals compete for resources, finally leading to no
growth (where birth rate and death rate are about the
same); therefore, it reaches its carrying capacity.
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
depend on the density or size of the population (the
greater the population size, the more competition for
resources that will limit the population size).
Biology 12 Answer Key Unit 5 • MHR TR
5
2. Abiotic factors such as cold weather could kill individuals
that would produce the next generation. Biotic factors
such as predators, or competition if the population
becomes dense enough, could inhibit the growth.
10. Since the snowshoe hare uses camouflage, I would
expect a change in colour to blend with the
environment in spring and in winter; brown in
spring and white in winter.
3. Sample answer: A cold snap kills all or most of the
mosquitoes in a pool of stagnant water.
11. Distinctive colours and patterns on some species
warning warn predators that they are dangerous. Other
organisms that are not dangerous mimic the dangerous
ones and so deter predators.
4. When density reaches a point at which biotic factors
like competition for food supply begins, reproduction
and the ability to survive are reduced. This results in a
decline in the population.
5. Sample answer: The population in the picture appears
fairly dense. I would expect intraspecific competition.
The number of nesting sites would determine the
carrying capacity of this habitat. The gannets will
compete for nesting sites and food when the population
gets above a certain number, and as a result, some
gannets will not reproduce successfully. Therefore, the
population growth will slow and eventually level off
when the habitat reaches carrying capacity.
6. Snakeweed was likely brought to North America with
travellers. It outcompetes native plants that have the
same habitat requirements and similar ecological
niches. Snakeweed survives and reproduces, often
excluding native plants.
7. Producers have a direct relationship with their
consumer population, just as a prey population
has a direct relationship to its predator population.
The scarcity of a producer limits the growth of the
consumer, just like the scarcity of prey limits the
growth of the predator. On the other hand, a large
population of consumers or predators may control
the growth of producers or prey.
8. Diagrams should resemble the Predator-Prey
Population Cycles representation shown in
Figure 11.29 on page 524 of the student textbook. As
the predator feeds on the prey, the prey population
decreases and the number of predators increases.
When the prey is no longer plentiful, the predators
must compete for prey so their population decreases.
As the predator population decreases, the prey
becomes more plentiful again, and the cycle repeats.
9. If the hare population is kept at a high and constant
level, the lynx population would increase to the
carrying capacity and remain there. If the lynx
population is kept at a high and constant level, the hare
population would greatly decline. The lynx will have
to compete for food and some will not survive, so the
biologists would need to introduce enough of them
into the environment to take the place of those that do
not survive.
6
MHR TR • Biology 12 Answer Key Unit 5
12. Both are defense mechanisms that use colour to
ward off prey. In Batesian mimicry, a species that
is not dangerous takes on the appearance of the
dangerous species, using their “warning colours” to
ward off prey. In Müllerian mimicry, two species that
may be poisonous, harmful, or unpalatable benefit
from mimicking each other in a co-evolved defense
mechanism—for instance, a predator that tastes or
becomes sick from preying on the poisonous species
will avoid the other.
13. Like predator-prey populations, parasite-host
relationships are density-dependent. An increase
in host population results in an increase in parasite
population, and this in turn causes a decline in the
host population. The reduced host population means
a reduced parasite population, and the surviving
parasites begin to increase again, since they do not
have much competition, and the cycle repeats.
14. Sample answer: Mutualism exists between bees and
the flowers they pollinate. The bees get food (pollen
or nectar) from the flowers, while the flowers get help
moving pollen from plant to plant for reproduction.
15. In mutualistic relationships, since both populations
benefit from one another and neither is competing, an
increase in one population provides more benefit to the
other, and these benefits cause the other population to
increase as well.
16. Mutualism is one of the symbiotic relationships
described. Since the bacterium lives in the host,
it benefits from the host, and since the bacterium
prevents cancer and acid reflux, the host also benefits
from the bacterium. Parasitism is the other symbiotic
relationship described. Since the bacterium lives in the
human stomach and causes harmful stomach ulcers,
the parasitic bacterium is benefiting and the human
host is being harmed.
17. Answers for intraspecific competition, may include
any competition for resources between members of the
same population. For example, grasshoppers eat grass
depriving members of their own population of food.
A male deer competes with another male deer of the
same species to mate with a female deer. Answers for
interspecific competition, may include any competition
for resources between two or more species. For
example, squirrels and chipmunks compete for food
and other resources (even though they nest in different
areas). A pine tree and a spruce tree compete for light,
space and other resources in a forest.
Answers to Chapter 11 Review Questions
(Student textbook pages 541–5)
1. b
2. d
3. d
4. a
5. c
6. d
7. e
8. e
9. c
10. a
11. a
12. c
13. e
14. d
15. Since the results have to be extrapolated to the
entire population, if the population is not uniformly
distributed, the resulting extrapolation for the number
of individuals in the population will be skewed.
16. Ecologists sample subsets of the populations using
transects, quadrats, or mark-recapture to determine
population density in a sample area, then extrapolate
the findings to the size of the entire area to determine
total population size.
17. For populations that are sessile, like plant populations,
or those that move very little.
18. When resources are not distributed evenly, populations
tend to gather near them in a clumped distribution
pattern. When resources are evenly distributed but
scarce, populations tend to be territorial and uniformly
distributed. When resources are evenly distributed and
plentiful, there is no need to share (or compete), so
populations tend to be randomly distributed.
19. Humans have a low fecundity, since they generally
produce one offspring at a time, which they raise for
many years, and it takes a long time for offspring to
become sexually mature.
20. In Type I survivorship, there is a high rate of survival
of individuals that live to sexual maturity or beyond,
so risk of mortality early in life is low. In Type II
survivorship, the risk of mortality is constant
throughout the individual’s lifetime. In Type III
survivorship, mortality is high early in life, however
those that do survive generally live long lives once
they reach adulthood.
21. The Type I survivorship curve has a high rate of
juvenile survival and individuals that live until
sexual maturity and beyond (e.g., human) I. In
Type II survivorship, the risk of mortality is the
same throughout the lifespan (e.g., hydra). In
Type III survivorship, most individuals die as juveniles,
although surviving individuals produce large numbers
of offspring (e.g., dandelion).
22. Factors that define biotic potential are all related to
fecundity. Answers should include any three of:
• the number of offspring per reproductive cycle
• the number of offspring that survive long enough
to reproduce
• the age of reproductive maturity
• the number of times the individuals reproduce in a
life span
• the life span of the individuals
23. The best way for species in unstable environments to
ensure survival of more offspring is to reproduce close
to the biotic potential (more offspring).
24. Density-independent factors are abiotic events such
as weather, floods, droughts, forest fires, hurricanes,
tornadoes, or urban development that limit population
growth in the same way, regardless of density. These
factors cause a steep decline in population growth.
25. When two species compete, one may out-compete the
other, excluding that species from the habitat. If the
niches are sufficiently different, they may both live in
the same area but the density of one may be lowered by
the presence of the other.
26. The parasite-host and the predator-prey relationships
are similar in that an increase in parasites/predator
populations causes a decrease the host/prey
populations. When the host/prey populations are
low, the parasite/predator populations eventually
decrease, which in turn causes an increase in
host/prey populations, and the populations continue
to cycle in that way.
Biology 12 Answer Key Unit 5 • MHR TR
7
27. Extinction is a possible outcome of interspecific
competition because when populations of two different
species compete, one may outcompete the other.
Meaning that it survives and the outcompeted species is
extirpated (at least). Extinction is not a possible outcome
of intraspecific competition because this competition is
between members of the same species, which means that
even if some of the population dies there will be other
surviving members to continue the population.
28. N = (originally marked × total in recapture)/
marked in recapture
N = (24 × 30)/9 = 80
The best estimate for the population of geese in that
area is 80.
29. cgr = ∆N/N = (21 - 15)/200 = 0.03 or 3%
The per capita growth rate is 0.03 or 3%.
30. gr = ∆N/∆t = (2200 - 1600)/2 = 300
The population increased at a rate of 300 beetles per year.
31. The average density in meadow A is
(6 + 10 + 8 + 5 + 11)/5 = 8 butterflies per plant,
which is 8 × 10 000 = 80 000 butterflies. The average
density in meadow B is (9 + 5 + 10 + 8 + 3)/5 = 7
butterflies per plant, which is 7 × 10 000 = 70 000
butterflies. Therefore, there are about 80 000 butterflies
in meadow A and 70 000 in meadow B.
32. Students should mention that the use of transects is the
best way to sample such large animals. One way is to
randomly determine the starting point and direction
for each of ten 1 km transects, and then count all the
moose within 50 m of the transect line.
33. Density = (8 + 6 + 9 + 12 + 4 + 10 + 8 + 7)/(25(8))
= 0.32 wildflower per m2. Since the conservation
area is 1 km2 = 1.0 × 106 m2, the population is
0.32 × 106 = 3.2 × 105, which is about 320 000.
Therefore, the population of this species of wildflower
is about 320 000.
34. 4/40 or 10% of the population is tagged. 10% of 500 = 50.
Therefore, the population of trout is about 500. The twoweek waiting period between samples may have resulted
in some of the tagged trout being caught by others,
contributing to the low number of tagged trout caught
in the second batch. The student could have caught the
second batch within a few days to reduce this possibility.
35. Population change is (90 + 5) - (10 + 6) = 79.
The per capita growth rate is 79/300 = 0.26. Therefore,
the per capita growth rate for this population is 26%.
8
MHR TR • Biology 12 Answer Key Unit 5
∆N
∆t
gr = 54/7 = 7.714
This population grows at the rate of 7.7 fish per year.
36. gr =
37. The predator-prey population follows a densitydependent cycle. As predators cause a decline in the prey
population, competition for food increases. Eventually
the predator population declines. With the decline in
predators, the prey population can begin to increases.
This cycle continues so that the prey population does
not get so low that all the predators die out.
38. Sample answer: With the absence of coral snakes,
predators could learn that snakes with those colours are
not poisonous and would increasingly prey on them.
39. Experimental designs should determine if the snakes
share other characteristics aside from appearance
(Batesian mimicry). If they share other defence
mechanisms such as being poisonous, harmful, or
unpalatable, the mimicry is Müllerian. Experimental
designs should take into consideration the safety of the
tester and respect for the living organisms being tested.
40. Sample answer: I would expect a steady increase in
population size until the population density reached
the carrying capacity of the island. Once the carrying
capacity was reached, population size would remain
fairly stable. Food supply is the most obvious limiting
factor. Overcrowding and disease might also be
limiting factors.
41. The introduction of foxes, natural predators of hares,
will cause a decrease in the hare population. As long as
an ample food supply (hares) for the foxes exists, the
fox population will continue to grow. However, as the
hare population declines, the fox population will begin
to decrease due to a limited food supply and perhaps
also due to overcrowding and disease. As this happens,
the hare population will begin to increase once again.
42. Answers may include abiotic factors such as extreme
weather, lack of water, or fires (loss of habitat) that limit
where deer can survive.
43. Plans should include protection for the birds and
their habitat (mountain regions and dry, rugged open
country and grasslands), consider requirements for
nest construction (cliff ledges, or trees in tundra),
ensure enough prey (small mammals), and ensure that
birds are spread out to reduce competition.
44. Table should compare the fecundity, survivorship, life
strategies, and limiting factors (predation, competition,
etc.) for the two species chosen. Answers should cite a
combination of these to help explain the success and/or
failures in the habitat.
45. Answers can consider the life span, age of sexual
maturity, number of offspring per reproductive
cycle, and the level of prenatal care to determine
which species is more K-selected (adapted to its
environment). Factors that put an organism at risk are
usually related to changes in the environment. Answers
should identify environmental changes and note how
formerly beneficial adaptations may now put the
mammal at risk.
46. Answers should indicate that resources are plentiful
(they eat both terrestrial and aquatic vegetation) and
that moose are good swimmers (i.e., have access to
wider territories). They experience little competition
for resources and have few predators (wolves on land
and killer whales in the ocean). Further, because
of their size, predators try to attack calves, which
are protected by the great deal of parental care that
moose provide.
47. Graphic organizers should indicate that symbiotic
relationships involve the relationship between a host
and another organism, in which one lives or feeds
of the other. They should also show the three forms:
commensalism, mutualism, and parasitism) and
include facts, concepts, and examples from their work
in this chapter.
48. Answers should include a definition and examples of
commensalism, mutualism, and parasitism.
49. Graphs should show exponential growth, such as in
Figure 11.16 on page 514 of the student textbook. Since
the bacteria is growing under ideal conditions without
limiting factors, it can reach its biotic potential.
Sample Method
Description
50. Graphs should combine the line features and labels of
Figure 11.17 on page 514 of the student textbook and
Figure 11.17 on page 515.
51. Pamphlets should include, in laymen’s terms, details
such as that the spiny water fleas flourish because
they have few predators and diseases in their new
habitats to keep their populations in balance. It should
also mention their high fecundity with a Type III
survivorship, which means they produce many eggs
and reproduce quickly. They have an r-selected life
strategy, living close to their biotic potential. Spiny
water fleas consume much more food than native
species, and as the population grows rapidly, they
disrupt the food chain. Because they are very small,
spiny water fleas and their eggs are easily transported
on boats and equipment.
52. Concept maps should show that birth and immigration
add members to the population of the species and
the predator population, while death and emigration
remove members from both populations. The concept
map should link the predator population, which also
contributes to death of members of the species to the
species population.
53. Cartoons should show a large prey/host population
providing much food for the predators/parasites,
allowing the predator/parasite population to increase.
With more predators/parasites, the prey/host
population declines, resulting in more competition
which decreases the predator/parasite population. With
fewer predators/parasites, the prey/host population
increases, and the cycle continues.
54. Sample answer: See below
55. There are not enough resources available, so organisms
must allocate resources either to current reproduction
or to survival; it’s a trade-off. A change that increases
reproduction, for example, may decrease survival.
Type of Organism
Calculation to Determine Population
Transect
randomly chosen
rectangular areas
low density, sessile, mobile,
or large
average number of individuals per transect
× total
total size of transects
Quadrat
randomly chosen sites
of a known size
sessile (or move very little)
average number of individuals per quadrant
× total
total size of quadrants
Mark-Recapture
capture, tag, release,
and recapture
highly mobile
captured in Batch 1 tagged captured in Batch 2
=
population
total in Batch 2
Biology 12 Answer Key Unit 5 • MHR TR
9
56. Posters should show:
a. random distribution
b. clumped distribution
c. uniform distribution
grown together, P. aurelia is more successful since it
out-competes the other, causing a decrease in the
P. caudatum population. This is interspecific competition
and demonstrates the competitive exclusion principle.
57. Sample table:
Birth Rate to Death Rate
Slow Growth
greater
Rapid Growth
much greater
No Growth
equal
58. Answers should include that in clumped distribution
patterns, the population clumps near resources, for
protection, and to care for the young. In uniform
distribution patterns, food is scarce and evenly
distributed, so individuals compete, giving rise to
territorial behaviour to defend resources. In random
distribution patterns, resources are plentiful and
uniformly distributed so there is no need to defend
resources, and the young can be distributed throughout
the area, at random.
59. Points may include that competition may cause species
to become extinct, limit population growth, and
evolutionary changes as well as maintaining balance
in the population and habitat.
60. Sample hypothesis: Increasing intraspecific
competition will limit the number of seedlings that
germinate. The ones that survive will compete for the
limited resources, which may also cause some of the
young plants to die.
61. The motility of the larvae disperses the young
away from the sessile parents, thereby reducing
intraspecific competition.
62. Answer may include that depending on the crop, a
predator that does no harm to the crop, or another
species that can out-compete the pest (but will not
harm to the crop) may be introduced. Another plant
that creates an unfavourable habitat for the pests,
therefore increasing competition and reducing their
reproductive success, may also be introduced.
63. Answers may include cold weather, forest fires,
increased competition, predators or disease. All
of these factors increase the death rate, therefore
limiting growth.
64. When grown separately, the two paramecia shows
logistic growth patterns (a lag period, followed by a
rapid growth period, and then a period of no growth
when the habitat reaches carrying capacity). When
10
MHR TR • Biology 12 Answer Key Unit 5
65. These species produce large numbers of offspring
and become sexually mature early in life. That means
they live close to their biotic potential, growing
exponentially. As a result, they are often found in large
numbers when conditions are favourable. In the case
of weeds, they often outcompete desirable grasses or
plants; and pests may be harmful in great numbers
(some are disease carrying, others feed on vegetation
such as flowers or vegetables).
66. Answers may include that white spruce forms a low
spreading canopy as it grows, while lodgepole pine
tends to grow straight and loses its branches on the
bottom two-thirds of the tree when the forest becomes
dense. This means that as the forest becomes more
dense, white spruce out-competes lodgepole pine for
sunlight. Interspecific competition is taking place.
67. This is Batesian mimicry. The colour of the monarch
butterfly warns predators away from this butterfly. By
mimicking the colours, the viceroy butterfly tries to
give predators the same warning. If the viceroy were
also unpalatable, predators who tasted the viceroy
butterfly would stay away from both viceroy and
monarch butterflies, and those who tasted monarch
butterflies would do the same. That would be
Müllerian mimicry.
68. a. Mutualistic, since both benefit from the relationship—
the ants get food and the plants seeds get dispersed.
b. Parasitic, because the ants benefit and the plants
are harmed.
69. Sample answer: The lake reached carrying capacity
with 1000 individuals, since it has remained that way
for a long time (8 years). Introducing more individuals
will increase competition for resources and increase
any predators that may prey on the walleye. These
limiting factors will result in a greater number of
walleye dying than being born, and eventually the
number will go back to being around 1000 individuals
(maybe dipping below that number, before stabilizing).
70. Bears have many K-selected life strategies, such as
long life spans, a relatively low reproductive rate, and
parental care of their young. They also adapt to their
environment. This suggests a balanced life history;
therefore equilibrial is a suitable term.
Answers to Chapter 11 Self-Assessment Questions
(Student textbook pages 546–7)
1. d
2. c
3. a
4. b
5. b
6. b
7. d
8. a
9. b
10. e
11. Parasite-host interactions can cause host populations to
decline and remain at relatively low densities, leading
to a decline in the parasite population. With the decline
in parasite populations, host populations can increase
again, leading to an increase in parasites, and a cycling
of the populations.
12. Parasite-host interactions can cause host populations to
decline and remain at relatively low densities, leading
to a decline in the parasite population. With the decline
in parasite populations, host populations can increase
again, leading to an increase in parasites and a cycling
of the populations.
13. Answers may state that resources (space, food, etc.)
required by the gulls were abundant as they were
growing rapidly and their habitat had not reached
carrying capacity. The gulls did not have to compete.
There were probably little limiting factors (such as few
predators and little or no disease), so the growth rate
was much greater than the mortality rate.
14. Diagrams and captions should make clear that
in parasitism the host is harmed and the parasite
benefits, both partners benefit in mutualism, and in
commensalism one partner benefits while the other
is unaffected.
15. a. Captions should relate to the rapid (exponential)
increase in population size over time.
b. Sample answer: The population is growing in ideal
conditions as it is rapidly increasing (birth rate is far
greater than death rate).
16. The density is (28 + 32 + 50 + 45 + 41)/(5 × 100 × 5)
= 0.08 trees per square meter. This is a good method to
use since the density is low and the organism is large.
17. The availability of resources (such as food), competition
among members of the population and between
this species and another with the same ecological
niche, disease, predation, and abiotic factors (such as
temperature) can limit the growth of the houseflies.
18. Graphs should look like Figure 14.29 on page 492 of
the student textbook. Sample caption: Most mammals,
such as bears and human, are Type I; many insects and
invertebrates, such as grasshoppers and oysters, are
Type III; and Type II organisms include organisms like
hydra and songbirds.
19. This is an r-selected life strategy, and a Type III
survivorship pattern. Since the crickets have many
offspring and only some survive, there is a high
mortality rate for the young, which is characteristic
of a Type III pattern.
20. Graphs should look like curve III in Figure 11.10 on
page 507 of the student textbook.
21. Sample answer:
Competing
for
Competition
Between who
Result
Intraspecific
members of
same species
(generally
the same
population of
that species)
resources
(such as food,
water, light)
decline in
population
Interspecific
populations
of two or
more species
resources
(such as food,
water, light)
species may
be extirpated
from habitat,
or species may
use different
resources
in habitat
22. In uniform distribution patterns resources tend to
be scarce but evenly distributed, and interactions
between members are negative. In random distribution
patterns, resources are plentiful and evenly distributed,
and interactions are neutral. In clumped distribution
patterns, resources vary and are clumped together, and
interactions are positive.
23. Sample answer: Decreasing aquatic plants decreases
the oxygen in the pond for fish and other organisms
that need the oxygen. The lack of aquatic plants also
reduces the available food for aquatic life that feeds on
these plants. This will increase competition for oxygen
and food, and there will be a ripple effect, decreasing
the populations in the pond as the ripple travels up the
food chain.
Biology 12 Answer Key Unit 5 • MHR TR
11
24. Sample answer: Adaptations: bitter taste (milkweed)
and quills (porcupine). Protective colouration:
camouflage (deadleaf butterfly), mimicry (Pueblan
milk snake), or warning colours (coral snake). Mimicry
includes Batesian (innocuous organism copies look of
a dangerous species) and Müllerian (two poisonous
species look similar).
25. Answers should be examples of relationships in which
both partners benefit, such as bees getting pollen from
flowers and cross-pollinating them as they go, and
bacteria in a cow’s intestine which receives nutrients in
the intestine while helping the cow digest food.
Chapter 12 Human Populations
Answers to Learning Check Questions
(Student textbook page 554)
1. Throughout most of history, human population growth
was fairly stable, showing very little increase. There is
a decline around the 1300s due to widespread disease.
Since that time, the population has grown exponentially.
(Student textbook page 565)
7. Biomagnification is the increased concentration of a
substance (e.g., pesticide, other toxin) at each trophic
level of a food chain.
8. The burning of coal releases mercury into the
atmosphere. The mercury falls to Earth through
deposition (such as precipitation) and either settles
directly in lakes or streams or is washed into them after
being deposited on land. Within the waterways, the
actions of anaerobic microorganisms transform the
mercury into methylmercury.
9. Deforestation in impoverished countries is often
caused by people trying to survive by selling forest
products or clearing land to farm.
10. Sample answer: Improved agricultural practices
that discourage deforestation and enhanced forest
management practices to promote reforestation.
2. The amount of time it takes for the population
to double.
11. Coal is an inexpensive and readily available source of
energy. For many people, including some government
leaders and policy makers, affordable energy costs
are more important than environmental protection
and outweigh the harm that burning coal does to
the environment.
3. Food supply was increased through agricultural
technology and domesticating animals. Predators
were staved off with weapons. Medicines controlled
diseases. Shelter provided protection from weather and
improved storage for food to prolong supply.
12. Plastic items are harmful to marine life because they
leach toxic substances and are often ingested, blocking
the digestive system. Plastics are still being released
into the oceans and will be a problem for a long time
because they do not decompose quickly.
4. Sample answer: I would expect Canada’s population
pyramid to have a rectangular shape because the
birth rate is only slightly higher than the death rate,
which means that the population grows slowly. The
population in each age category tends to be about
the same.
5. The population would be shrinking (more deaths than
births). Also, a large number of individuals would
be past their reproductive years and few would be
about to enter their reproductive years. In this type of
population, there will be a significant burden on the
proportionally small number of working people to
meet the obligations of the government and to support
number of older people who have retired.
6. The human population was much greater in the 1900s
than in the 1300s when the bubonic plague occurred.
Because the change in the population in the 1900s
was not significant when compared to the size of the
population at that time, the decline does not show up
on the graph.
12
MHR TR • Biology 12 Answer Key Unit 5
Answers to Caption Questions
Figure 12.3 (Student textbook page 552): Differences in
the availability of clean water and healthy food. Differences
in access to modern medical technology to treat disease
and injuries would also affect the survival of members of a
population, as would economic disparities that could limit
access to suitable shelter.
Figure 12.5 (Student textbook page 555): If humans
continue to exceed the biocapacity of Earth the resources
will not be sufficient to support the population. Earth’s
capacity to supply resources will likely be degraded as
available land is used for other uses or water is polluted
and becomes unusable.
Answers to Section 12.1 Review Questions
(Student textbook page 556)
1. Humans have a small number of offspring, begin
reproduction later in life, and provide a lot of parental
care, like other K-selected species.
2. The existing land would have had few resources and
there were not enough resources to support new
populations. Competition and other density-dependent
factors, such as disease, would limit the population
until a time that humans could increase the carrying
capacity of their environment.
for little growth, and the large population growth
of the developing countries will account for most
of the increase in world population. Therefore,
Africa will contribute much more to the world’s
human population growth than North America and
Europe combined.
3. From the beginning to about the 1500s, the population
was fairly stable following a logistic growth pattern.
This is most likely due to density-dependent factors
since the environment was operating at or near its
carrying capacity at that time. After that period, the
population grew exponentially since new technologies
were developed, starting the Agricultural Revolution.
Humans were able to increase the carrying capacity of
the environment by planting and harvesting crops and
by domesticating animals.
8. Population pyramids should be rectangular for the
industrialized country and triangular for the lessdeveloped country. Students should explain that about
the same numbers are in each age category in the
industrialized country. In the less-developed country,
there is a large base that is below maturity. Growth will
be slow in the industrialized country since many in the
population are post-reproductive and have a long life
span; proportionately, there will not be as many births
in this country. In the less-developed country, many
are below maturity. When they reach reproductive
years, the population will grow rapidly.
4. Sample answer:
Developed
Countries
Developing
Countries
Growth Rate
grows slowly
grows more quickly
General Age
Structure
about equal across
age categories
large number of
young compared to
older people
Fertility Rate
low
higher
Shape of
Population
Pyramid
more rectangular
more triangular
Doubling
Time
much slower than
world average
quicker than world
average
Use of
Resources
use much of the
world’s resources
use little of the
world’s resources
5. If a large number of women in a population are
entering their reproductive years, the population
has the potential to increase since the birth rate can
be significantly greater than the death rate. On the
other hand, if much of the population is past their
reproductive years, then deaths will outnumber births,
leading to a decline (or slow growth, depending on the
size of the population).
6. To maintain the current standard of living, the number
of jobs, water, food, energy, homes, and other human
requirements would need to double. This would put
great demand on resources, which would not have time
to replenish and support the population.
7. The areas in North America and Europe covered by
developed countries are significantly greater than
areas of Africa covered by developed countries.
The population in developed countries is projected
9. It will depend on the ability to limit population growth
and per capita resource consumption.
10. Although the growth rate is decreasing, there are more
people present to reproduce.
11. People in industrialized countries pose a greater
burden (use a lot more resources and produce more
GHGs) than people living in less-developed countries.
12. The average Canadian requires 7.5 hectares while
the average person on Earth requires 2 hectares, so the
average Canadian requires 5.5 more hectares than the
average person.
13. The three largest components of the ecological
footprint in most developed countries are energy, food,
and forestry requirements. Each person can reduce his
or her energy use, take steps to reduce food waste, and
reduce greenhouse gas emissions.
14. Answers should indicate that the ecological footprint
for North America (just over 9 hectares) is much greater
than its available biocapacity (just over 2 hectares), while
the ecological footprint for Middle East/Central Asia
(just under 3 hectares) is about the same as its available
biocapacity. However, both regions are above the global
average (about 2 hectares). Africa’s ecological footprint
is just over 1 hectare and its biocapacity is just slightly
higher. Africa is below the global average.
15. The carrying capacity of Earth is probably not
static. It likely varies with factors such as weather,
environmental conditions, and the amounts that
people consume.
Biology 12 Answer Key Unit 5 • MHR TR
13
16. Sample answer: One graph shows the population
increasing and then stabilizing (or increasing, and then
decreasing before stabilizing). The carrying capacity of
Earth has been maximized so the population increases
to its maximum before stabilizing. The other graph
shows continued growth. Humans have developed
new technologies to improve low-production areas,
open oceans, and/or other planets/moons in the
available biocapacity.
17. The population pyramid indicates a large number
of young and those entering their reproductive
years. An explosive growth can be predicted for this
population. The advantage is that adding more people
could possibly make the nation and its economy
stronger as more people become available to work. The
disadvantages could be a shortage of resources such
as food, a drain on the economy as government has to
support schools, the healthcare system, and so on, and
possible degradation of the environment.
Answers to Section 12.2 Review Questions
(Student textbook page 569)
1. Coal burning is the main source of electricity
production. As the human population grows, the use of
coal to generate electricity increases. Other resources,
such as renewable forms of energy (wind, solar) and
nuclear energy also increase in proportion. Increased
coal burning is a problem since it is harmful to the
environment, contributes to global warming, and
releases GHGs and toxic metals into the atmosphere,
and thus, into our ecosystems.
2. a. Answers should include that carbon dioxide
emissions result in global warming, which affects
the entire world.
b. Sample answer: A maximum CO2 emission for
the entire world should be determined. Then, each
country should be given a maximum in proportion
to its population. Countries could buy and sell their
allotment to other countries if not used.
3. Food webs or chains should begin with producers,
such as algae or aquatic plants, and then show primary
consumers such as minnows, tadpoles, aquatic insects
or small fish or amphibians. Secondary consumers
could include larger fish, as well as shore birds (herons)
and gulls, guillemots or other birds know to consume
fish or small animals.
14
MHR TR • Biology 12 Answer Key Unit 5
When a toxic substance gets into the water, it is taken
in and builds up in the tissues of organisms in lower
trophic levels. This toxin is not removed from their
bodies. As higher level organisms consume lower level
organisms, they ingest the toxin. As a result, the toxin
is more concentrated in higher level organisms such as
sea bird.
4. Sample answer: Educate people about problems caused
by deforestation, such as soil erosion and mudslides,
loss of soil fertility, reduced cooling ability, and loss
of beauty. Provide jobs to replant the forests, which
will replace the income loss. Plant crops to feed the
population as the soil regains fertility.
5. Trawling sweeps the ocean floor, removing nearly all
the plant and animal life in its way, including corals,
fish, and other organisms.
6. A large number of sea turtles have been caught as
bycatch, causing a decline in the population. Since
many young sea turtles are also caught before they have
time to breed, sea turtles are not able to recover.
7. The millions of tonnes of garbage people dump into the
sea gather where water flow is slow or where currents
keep garbage in a certain location. The main problem
with such garbage patches is that it releases toxins and
is ingested by marine life. Either the toxins biomagnify
along the food chain or the structure of the garbage
harms the animals’ organs.
8. Nurdles contain chemicals that mimic estrogen and
disrupt the endocrine system of marine life leading
to feminization of males. This causes reproductive
problems. Nurdles contain high concentrations of
mercury and pesticides which leach from the nurdles
into the bodies of organisms that ingest them. These
toxins biomagnify with each transfer along the food
chain, affecting the top predator the most.
9. Sample answer: Biodiversity stabilizes the ecosystems
that we rely on for materials, food, and medicine,
thereby making them—and the economies that rely on
them—resistant to change.
10. a. Answers may include the use of reusable bags,
charging for disposable bags (discourages use), and
banning plastic bags. This is necessary for reasons
such as reducing the volume of plastic bags in
landfills and waterways and reducing the drain on
fossil fuel resources.
b. Answers may include reusing materials and using
alternative reusable materials for containers,
clothing, and so forth.
11. The pest will attack the corn and the entire crop will be
lost since the corn is less resilient to change.
14. e
12. Habitats loss and fragmentation limit the size and
movement of populations, and increases competition.
Habitat degradation may introduce invasive species
that out-compete native species, eliminating them from
the habitat.
16. Advances in technology allowed the human population
to increase carrying capacity by increasing the
availability of food, preventing and controlling
diseases, providing better shelter, improving food
storage, and improving defences from predators.
13. Cartoons should show an accidental method (e.g.,
in ballast water of ships or in wood products such as
crates) and a purposeful method (e.g., as ornamental
plants or pets, or to help with environmental problems
such as soil erosion). The general effect is that the
invasive species take over habitat, decreasing or
eliminating native species.
14. Humans can make sure that they do not contribute to
the loss of habitat, overexploitation, pollution, or the
introduction of invasive species or disease.
15. Sample answer: Design a city that uses renewable energy
and active transportation, discourages the creation
of garbage (e.g., excessive packaging), reuses waste
materials and maximizes recycling, conserves water, uses
drought tolerant plants, and uses agricultural methods
that reduce pesticide and fertilizer use.
16. The reusable cloth bag may be reused again and again,
preventing the disposal of dozens of plastic bags which
are difficult to break down and fill up our landfills and
waterways where they release toxic chemicals into
the food chain. Producing the reusable bag may also
require fewer resources.
Answers to Chapter 12 Review Questions
(Student textbook pages 580–3)
1. e
2. c
3. e
4. b
5. a
6. c
7. c
8. b
9. e
10. d
11. c
12. e
15. b
17. The death rate has decreased even though the birth
rate has remained the same; therefore the population
continues to increase rapidly.
18. The doubling time decreased from 200 years between
1650 and 1850 to 45 years between 1930 and 1975. To
maintain the same standard of living, resources and
human requirements need to double to accommodate
the increase, putting more stress on the planet.
19. Population pyramids for more developed countries
are generally more rectangular, with about the same
amount of people in each age category. The birth
rate is generally not much greater than the death
rate, so these countries tend to grow slowly. In less
developed countries, the population pyramids are
more triangular, with a large number of young people
compared to older people. As the young people enter
their reproductive years, the birth rate is much greater
than the death rate, so these countries tend to grow
much more quickly.
20. So far, humans have been able to increase Earth’s
carrying capacity. In addition, people in less developed
countries operate below the average ecological footprint
which may somewhat balance the much higher
footprint of developed countries.
21. These pollutants are released from fossil fuels, which
enter the atmosphere as a side effect of burning and fall
into waterways as precipiation.
22. Pollutants biomagnify in the food chain. Producers and
consumers in the bottom trophic levels will have less of
the pollutants and pesticides. Eating kelp, rather than
fish, places humans at a lower trophic level.
23. There are fewer trees to remove carbon dioxide from
the air and the soil loses shade and protection from
erosion provided by roots.
24. Sample answer: Technology such as dredging and
trawling collect both wanted and unwanted species,
leading to serious decline in marine populations.
25. Plastics, because they release toxins and harm wildlife
when eaten (or entangled).
13. c
Biology 12 Answer Key Unit 5 • MHR TR
15
26. Answers may suggest big cities produce the most
pollution since they require the most energy (for
electricity production, heating & cooling, and
transportation) and produce the most waste. Others
may support the idea that areas with heavy resourcebased industries produce the most pollution. Accept all
reasoned and supported answers.
31. Once the average number of births per couple falls
to 2 worldwide, there will be low population growth.
However, the overall population will continue to
increase since parents generally live for decades after
children are born, and those children will most likely
have children before grandparents die (assuming the
same life expectancy everywhere in the world).
27. Modern techniques such as monoculture limit
biodiversity, resulting in crops that are susceptible to
disease and pests. Increasing the yield of land puts
an unnatural drain on soil nutrients and requires
additional pesticides and fertilizers.
32. Triangular, because there are a lot more people in the
younger age groups than the older ones. Since a large
part of the population will enter their reproductive
years at the same time, the population will most likely
experience explosive growth.
28. Answers may include loss of resources (materials,
food, medicine, clean water and air), vulnerability
to disasters and disease, loss of beauty. It also has
psychological and spiritual consequences.
33. Answers should show a fairly rectangular population
pyramid and predict that the Canadian population will
grow slowly.
34. Population in the next year is 310 million × 1.0055
= 311 705 000. The second year, the population
is 311 705 000 × 1.0055 = 313 419 377. The third
year, the population is 315 143 184. The fourth year,
the population is 316 876 471. The fifth year, the
population is 318 619 292. About 8.6 million people
will be added to the population in five years.
29. Answers may include cutting down forests to clear
land for farming and building, limiting biodiversity
by overexploiting resources and through pollution,
and using up resources such as fossil fuels. Positive
alterations include preservation of species risking
extinction and increasing the carrying capacity.
30. The two graphs show a similar trend, in that the
populations are increasing rapidly. Predictions may
be that the world population will somewhere between
8 and 14 billion in 100 years, and that the Canadian
population may be 50 to 80 million. Answers should
mention carrying capacity and predict whether human
behaviour can sufficiently change to increase the
carrying capacity to the upper limits, or whether the
population will level off at the lower limits.
World and Canadian Populations
35
25
20
38. Sample answer: We do not have enough alternative
electric generating capabilities to stop coal-based
power generation immediately. Also, coal is relatively
inexpensive when compared to generating energy
from cleaner sources.
15
10
World population
(in billions)
5
5
0
20
2
5
20
0
0
19
7
5
19
5
0
19
2
5
19
0
0
18
7
5
18
5
0
18
2
5
18
0
17
7
17
5
0
0
Year
36. About 11 billion hectares make up Earth’s biocapacity.
If each member of the human population requires
2 hectares, Earth should be able to support
11 billion ÷ 2 = 5.5 billion people. The current
population is 6.9 billion, which is 1.4 billion more
than Earth should be able to support.
37. Carrying capacity is based on cropland, grazing land,
fishing grounds, forest land, carbon-absorption land,
and building area. The stability of many of these
variables changes over time, making it difficult to
estimate the carrying capacity of Earth.
Canadian population
(in millions)
30
35. In many developed countries people are choosing to
have fewer children, and there is a high prevalence of
HIV/AIDS in some populations where fewer children
are reaching adulthood and adults are dying at a
younger age.
39. Sample answer: test the air in enclosed garages to
determine the amount of carbon dioxide present and
then run each car for the same amount of time before
testing the air again. When testing for carbon dioxide,
bromothymol blue will cause the solution to change
colour and then adding sodium hydroxide changes
World and Canadian Populations
16
35
30
MHR TR • Biology 12 Answer Key Unit 5
Canadian population
(in millions)
the colour back. The more drops of sodium hydroxide
needed to change the colour back, the greater the
amount of carbon dioxide.
40. Sample answer: local communities have to be
convinced that it is in their best interest to conserve the
forests. At the same time, alternative sources of income
and economic efficiency need to be provided for
them. Promote the abundance of species by creating
conditions favouring their growth and development,
prevent outright destruction of the forests through
education and legislation, and improve current
agricultural lands and cultivation methods to prevent
further deforestation for farming.
41. Answers should include reducing waste by purchasing
returnable, reusable, or refillable items, buying in bulk,
composting, using double sided printing/copying and
reusing old paper, buying upgradable electronics, and
buying items that can be recycled.
42. Plastic does not biodegrade, so it is very durable and
thus widely used. Because it only breaks into smaller
pieces, we have problems disposing of it, and it harms
animals when they ingested it.
43. Hypotheses might include that humans have a positive
impact on the carrying capacity of Earth because they
increase its carrying capacity through technological
advances which increase food supply and resources,
and preserve endangered/threatened species.
Or, hypotheses may state that humans have a negative
impact on the carrying capacity of Earth, because they
decrease its carrying capacity for other organisms
through pollution, limiting biodiversity, overexploiting
species, and destroying habitats.
44. Sample answer: a terrarium containing soil, plants,
water, and worms or snails. Factors in the ecosystem
work together such that the plant uses water, carbon
dioxide and sunlight to produce food and oxygen for
the snail, while the snail produces carbon dioxide for the
plant to use. The systems work to sustain one another.
The ecosystem would be unsustainable if the snail
population increased, exceeding the supply of resources,
or if the environment became polluted by snail waste,
or if the plant died or was not able to produce enough
oxygen (e.g., lack of sunlight or water hurt the plant).
45. Answers should indicate that the minimum viable
population size must be determined, considering a
number sufficient for little or no interbreeding, and
which ensures there is sufficient genetic diversity in the
pigs which are transported so that they can adapt to the
new environmental conditions.
46. On the pro side, answers may include that the
population has expanded so much that it is using
more resources than can be replenished, and therefore
is destroying Earth. Poverty in many nations and
destruction of the environment are evidence of
overpopulation causing stress. On the other side,
answers may note that it is not the number of people,
but the unnecessary amounts that we consume, waste
and exploitation that place stress on the environment.
People living in the poorest countries use only about
1.3 percent of the resources and emit 3 percent of
the carbon dioxide, so it is the behaviour in wealthy
nations that stresses the environment, not the
population level.
47. Country A has a triangular population pyramid
because the percent under 16 years old is so much
larger than the population of over 65. Country B also
has a triangular pyramid (with a narrower base than
Country A), since the percent of people under 16 is
significantly greater than those over 65. Country C’s
pyramid is rectangular because the population under
16 is close to the number that are over 65. Country
D has an inverted triangle shape, since the under
16 population is less than that over 65, indicating a
shrinking population.
48. Answers should mention that burning coal produces
pollutants that cause acid rain and photochemical
smog that contribute to global warming, which harms
people and the environment. It produces mercury,
which pollutes our waterways and food supplies.
Answers may suggest using renewable forms of energy
such as wind, solar, hydroelectric, and geothermal.
49. Sample answer: Renewable energy is less harmful than
non-renewable energies are. Non-renewable energy
such as coal and natural gas are fossil fuels. When we
burn fossil fuels they produce pollutants that harm
our air and water, and consequently, our food. The
heat pollution and smog effects also affect weather.
Renewable energy comes from natural phenomenon
such as wind, solar, geothermal, and hydroelectric
sources. Wind and moving water can turn turbines to
create electricity and the Sun’s heat can be captured and
used for heating or to create electricity, as can the heat
from within Earth.
50. Answers may include growing and harvesting food;
transporting, storing, processing, and preparing food;
and energy used in the food trade (buying and selling).
Biology 12 Answer Key Unit 5 • MHR TR
17
51. a. Food chains should include producers, primary
consumers (herbivores), and secondary consumers
(carnivores and omnivores), as well as food products.
b. Humans can fulfill all their nutritional needs with
grain-based foods without having to depend on
animals, which require many more resources
to produce.
52. Arguments should include the values of biodiversity
such as providing humans with: species for medicines;
stable ecosystems which regulate climate, provide
fresh water, prevent soil erosion, and so on; beauty;
and spiritual and psychological benefits, linking to
emotional well-being.
53. a. Introduced species include purple loosestrife, Asian
carp, giant hogweed, and the spiny water flea. A
full list of species, their source and impact can be
found on the Hinterland Who’s Who website under
Invasive Alien Species in Canada.
b. Answers should mention that invasive species
reduce resources available to other species, or prey
on them directly. Without controls, invasive species
limit biodiversity and may extirpate native species.
54. Answers may include environmental consequences
such as loss of species and habitats, soil erosion, and
increased carbon dioxide, which contributes to global
warming and adverse weather patterns. They may
also include that the indigenous people whose homes
are destroyed are not compensated, while companies
and consumers profit. Alternatives may encourage
consumers to instead use environmentally friendly
woods and other materials.
55. Sample answer: Yes. Canada has 10 percent of the
world’s forest and represents about 0.4 percent of
the world’s deforestation in response to demand for
resources and land. Although reforestation occurs in
Canada, 90 percent of the forests are not protected.
People should be educated about the problems
associated with deforestation and we should continue
to replant and protect forests.
56. HIV would spread most rapidly in a triangular
population age structure because most of the
population is entering reproductive years, and has the
potential for many newborns. HIV is easily spread
from individual to individual and to unborn/newborn
children. In other age structures, there are fewer people
entering reproductive years, so there would not be as
many newborns for HIV to spread to.
57. a. A lower birth rate should put less strain on the
economy, fewer food shortages, and less stress
on environmental resources and ecosystems (less
pollution, cutting down of forests for food and
building, overexploitation of species, etc.).
b. Disadvantages include a small youth population to
take care of a large aging population, a smaller work
force, and fewer consumers. Traditional preference
for male offspring has resulted in a gender
imbalance that has far fewer females that normally
expected. This will further depress population
growth and is leading to social problems as young
men reach maturity and there are no mates for them.
58. Sample answer: Stop deforestation and replant forests.
Forests retain a lot of water and prevent soil erosion,
both of which help control water levels. If forests
are not restored, floods will continue to damage the
ecosystem and its inhabitants, and may worsen.
59. Answers may include laws and programs to educate
fishermen and consumers about loss of species,
reduce water pollution, reduce overharvesting and
bycatch, and reduce invasive species. They may suggest
imposing a moratorium during certain periods (e.g.,
spawning and growing times), or impose fines for fish
of a certain size and for a specified amount of bycatch.
60. a. Plastic bottles are light, convenient, and inexpensive,
recyclable, and reusable.
b. Plastic releases toxins into the things it contains,
and into the environment during production and
when disposed of (whether in a landfill, waterway,
or incinerator). Pieces of plastic bottles are often
mistaken for food and harm animals when ingested.
The space taken up for the disposal of plastics (and
when the plastic escapes containment, as litter)
threatens the habitats of terrestrial life.
61. Cars produce carbon dioxide emissions and
pollutants which contribute to global warming and
photochemical smog. We can reduce these problems by
driving less (using active or mass transportation, or by
car pooling) and by using vehicles that use less fuel and
cleaner fuel.
Answers to Chapter 12 Self-Assessment Questions
(Student textbook pages 584–5)
1. e
2. d
3. e
4. a
18
MHR TR • Biology 12 Answer Key Unit 5
5. a
6. b
7. a
8. b
9. a
10. c
11. Answers should mention that in these dumps, only a
small amount of marine life survives. When marine
life ingests the plastics in these dumps, their organs
are damaged and toxins get concentrated in their
tissues which biomagnifies with each transfer along
the food chain. This ends up harming humans.
The connectedness among the oceans’ ecosystems
means that these garbage dumps affect global marine
ecosystems, including those off the Canadian coasts.
12. Answers should mention that advances in technology
would allow the human population to increase its food
supply and the lifespan of food, advance medicine
to cure and control fatal diseases, and provide better
shelter from the elements.
13. Graphs should be similar to Figure 12.1 on page 550
of the student textbook. The population was relatively
stable until about the 1700s (with a slight dip around
mid 1300s due to disease) since density-dependent
factors limited the population at that time. After
that time, technology allowed humans to increase
the carrying capacity of the environment, leading to
exponential growth.
14. At the start, the difference in population between the
two countries is 21 million - 19 million, or 2 million.
The population of Country A after one year is
(1 - 0.004)(21 × 106) = 20.916 million, and after
two years is (1 - 0.004)(21.912 × 106) = 20 832 336.
The population of Country B after one year is
(1 + 0.008)(19 × 106) = 19.152 million, and after two
years is (1 + 0.008)(19.152 × 106) = 19 305 216. The
difference after two years is 20 832 336 - 19 305 216
= 1 527 120.
15. Ecological footprint refers to the amount of land
needed to support each person (or any identified group
or thing). The difference is mainly due to the difference
in the standard of living in different countries—more
developed countries have a larger footprint than
developing countries do.
16. Answers should include the use of renewable
energy and resources, the sustainable use of water,
food sources (fishing and agriculture), responsible
waste management, using as little as possible and
replenishing as much as possible.
17. Bar graphs should show that the percent of young (at
or below their reproductive years) is much greater than
the older population (those past their reproductive
years). Answers should explain that population growth
represents the difference between birth and death rates,
and in this population the number of births will far
outnumber the number of deaths, so the population
will show rapid growth.
18. Scientists divide the total of the biologically productive
areas (Earth’s biocapacity) by the population to
determine if the population has exceeded the available
biocapacity. This assumes that no land is set aside for
species that consume the same biological material
as humans.
19. Diagrams should show that burning fossil fuels release
mercury into the atmosphere where it falls back to the
ground in precipitation. This water carries the mercury
into the ground and waterways where it enters the food
chain and accumulates in fish, which humans eat.
20. The plants and animals in forest fragments are
vulnerable and may even become extirpated. These
organisms’ genetic diversity is reduced. The movement
of animals to find mates and food are restricted and
species often cannot complete migration. This limits
the biodiversity in the forests and puts the organisms
at risk.
21. Answers may include public awareness to reduce
overharvesting and bycatch, prevent illegal and
unregulated fishing, reduce pollution, control
invasive species, and protect marine areas to maintain
resilient ecosystems.
22. The increased demand for resources due to demand in
the developed world, human population growth, and
increased development in formerly underdeveloped
societies puts a strain on Earth’s resources. The more
people there are, the more of the world’s resources are
required to provide energy, food, and shelter. We need
many solutions that work together by reducing the use
of resources, replenishing resources, and disposing of
waste responsibly.
23. Sample answer: Farmers may use a monoculture
technique to increase crop yield. This may result in an
ecosystem with little diversity. To increase biodiversity,
they could rotate crops, plant a variety of crops, remove
and control invasive species, restore degraded habitats
on their properties, protect existing properties, manage
fields for native birds, pollinators, and animals, and use
pesticides sparingly.
Biology 12 Answer Key Unit 5 • MHR TR
19
24.
Country
Kenya
General Age Structure
Pyramid
Shape
Future
Growth
large number of
young compared to
older people
triangle
explosive
Sweden
age categories are
about equal
rectangle
slow
Germany
fewer young compared
to older people
inverted
triangle
shrinking
25. Animals with high methylmercury levels exhibit
interference in their growth, development, and
reproduction; damage to kidneys, lungs, liver, nervous
system, and immune system; and interference with
brain development.
Answers to Unit 5 Review Questions
(Student textbook pages 589–93)
1. a
2. e
3. b
4. d
5. c
6. a
7. a
8. d
9. b
10. d
11. e
12. e
13. c
14. c
15. c
16. e
17. A uniform distribution pattern results from lack of
resources causing competition and territoriality. A
clumped distribution pattern results from habitat that
is irregularly distributed, or asexual reproduction.
A random distribution pattern results when one
individual has no effect on the location of another and
resources are plentiful.
18. This survivorship curve indicates that a large amount
of seeds are produced, but the young seedlings have
a low survivorship rate. Little energy is put into
individual seeds and more is put into producing many
seeds. This represents an r-selected life history.
20
MHR TR • Biology 12 Answer Key Unit 5
19. Population growth rate measures the increase in
a population over a certain period of time, and is
expressed as a percent of the initial population. It
takes into account the number of births, deaths,
immigration, and emigration.
20. The typical shape of the growth curve for most
populations is an S-shaped curve. This growth curve
has a slow initial growth, followed by exponential
growth (when the population is growing at its biotic
potential), and finally stable numbers.
21. Interspecific competition occurs between two or more
species, while intraspecific competition occurs among
members of the same species.
22. The mistletoe will cause damage to the oak tree since
the mistletoe is a parasite. In a parasitic relationship the
parasite benefits and the host (the tree) is harmed.
23. The age patterns in a population pyramids differ for a
poverty-stricken country (triangular) and a wealthy
industrialized country (rectangular).
24. Answers include lower fecundity.
25. Biologically productive surface land, cropland, grazing
land, fishing grounds, forest land, and building areas
are used to determine Earth’s available biocapacity.
26. Sample answer: Burning fossil fuels for energy puts
harmful pollutants in the air, which depletes the ozone
layer and increases UV ray transmission, which cause
skin cancer. It also releases toxins in the air and water.
The toxins biomagnify along food chains, ending up in
large amounts in humans.
27. A greater need for energy results in burning fossil fuels,
putting toxins in the air and water, and consequently
in the food chain. A greater need for food results in
deforestation in order to farm, and in overharvesting of
species such as fish. A greater need for waste disposal
results in garbage in the oceans (killing marine life),
and also results in filled-up landfills.
28. No. Monoculture is a technique in which only one
species of crop is planted. That means monoculture does
not contribute to a variety of plants in the ecosystem.
Since there is only one type of crop, only certain types
of consumers will live in that environment, limiting the
biodiversity of the ecosystem.
29. More biodiversity creates diverse interactions among
organisms, and more diversity in the food web. That
means the ecosystem can more easily compensate
for environmental changes. When the ecosystem is
not very diverse, organisms are more dependent on a
smaller number of species and are more specialized
and vulnerable to environmental changes.
31. Pesticides and toxins enter the soil and water, where
they get into the food chain. The toxins in pesticides
biomagnify as they are passed along the food chain.
32. Answers should mention quantitative measures such as
population size, density, distribution, and life history.
33. a. Answers may suggest mark-recapture, a method in
which a certain number of the owls are captured,
tagged, and released. A second capture at a later date
considers the number of previously tagged owls that
are captured and extrapolates that to estimate the
population size.
b. Sample data:
Captured and marked
100
Recaptured
90
Number marked in second capture
20
c. 100/x = 20/90, x = 450
40. Water, light, and temperature are abiotic factors that
affect producers and limit the amount of producers.
Since the producers are food for some consumers,
the amount of food available for these consumers
limits their population, which also limits the higher
level consumers that consume the primary consumer.
Some consumers also require water for physiological
functions, and light/temperature for reproductive
functions. Therefore, varying these factors influences
the growth of these populations.
41. Sample graph:
E. Coli under ideal
conditions in Petri dish
E. Coli in
animal’s
intestine
Time
30. Extirpation of a species or at least a threat to survival.
34. Population density is the number of individuals per
unit area. The population density is 975 ÷ (100 × 200)
= 0.075 per square metre.
35. There are 150 ÷ 10 = 15 cattails per square metre.
The population of cattails in the marsh is 15 × 10 000
= 150 000.
36. Since the organisms are large, the ecologist should
use transects to sample the population and then
extrapolate to find the population. Answers should
mention randomly determining starting points and
direction for a number of transects, and specify the
length (e.g., 100 m) and distance from transect line. A
description should be included for how to calculate the
population by finding the number of birch per square
unit and multiplying that number by the total area.
37. -11: gr = ∆N/∆t,
∆N = final number - initial number
= 15 872 - 15 916 = -44
∆t = final time - initial time = 2007 - 2003 = 4
gr = -44/4 = -11 elephants per year
38. The final number of foxes is 466. Since ∆N = 14, the
original population (N) can be calculated by 3.1%
∆N = ∆N. Therefore, N = 14/3.1% = 451.6129
The total number of foxes (final number)
= ∆N + N = 14 + 451.6129 = 465.6129 = 466
39. The number of deaths is 62:
∆N = b + i - d - e and we are given i = 27,
b = 200, e = 15, ∆N = 500 - 350 = 150. Therefore,
d = b + i - e - ∆N = 200 + 27 - 15 - 150; d = 62
Population
The E. coli under ideal conditions has no limiting
factors and grows exponentially, at its biotic potential.
The E. coli in the animal’s intestine will experience
density-dependent limiting factors which will level off
the population when it reaches carrying capacity.
42. The population will explode since there are a lot of
young that will mature and have a litter of six or
more. There will always be a lot of young to add to
the population. However, when the environment
reaches carrying capacity, limiting factors will limit the
population and cause it to level off.
43. Data for world population by age can be found on the
US Census Bureau website at http://www.census.gov/
ipc/www/idb/worldpop.php. Population pyramids
should be somewhat regular, with the explanation that
the numbers in each age category are similar. Since
there are many people at or below child-bearing years,
the population will continue to grow as births exceed
the death rate.
44. Answers should mention measuring the mass, growth
plates, teeth, etc. (quantitative measures). and may
examine mating behaviours and their role in wolf
packs (qualitative measures). These measures can
determine age groups of individuals to create the
population pyramid.
Biology 12 Answer Key Unit 5 • MHR TR
21
45. The population in one year is
(8.5 × 104)(1 + 0.025) = 87 125 in one year, and
(8.7125 × 104)(1 + 0.025) = 89 303 after two years.
46. The number added in the first year is 340 000. If the
same number was added each year, it would take
100 years to double. However, the new amount that
is added is included each time, making the doubling
time less than 100 years. It would take about
34 × 106 × (1 + 0.01)x = 2(34 × 106), where x is
the number of years to double. This results in about
70 years to double the population.
47. Answers should take into account the following:
• estimated amount of food consumed
• energy requirements for heating, transportation,
operating average home appliances
• amount of waste generated
The numbers may be averaged across the class. Then,
determine the number of square meters of land needed
to support the average person’s annual consumption.
Those in the Yukon Territory may have different energy
consumption patterns due to the different climate and
longer hours of daylight and darkness in the winter and
summer seasons; in addition, transport of items like
food and fuel may increase their ecological footprint
unless they eat locally.
48. The populations follow a sinusoidal pattern in which
increase in the hare population causes an increase in
the lynx population, which then decreases the hare
population and is followed by a decrease in the lynx
population, once again resulting in an increase in the
hare population.
49. Suggestions may include increasing the mollusk
population to control the alga. The potential danger
in this is that because the mollusks are native to the
environment, there must be other native food sources
for them. They will also feed on this food source
(especially when the alga gets low), and may put the
native species at risk, disrupting the entire ecosystem.
50. Methods should provide a method and system of
reporting to get population numbers, population
density, number of contagious people, number of sick
days reported, contagion rate, percent of population
affected, population mixing, number that die, etc.
51. a. Compare the height and leaf size of those that are
planted close together with those that are planted
with optimal room.
b. Overcrowding is a density-dependent limiting
factor, so those plants are competing for light, space,
nutrients, etc. The plants should be smaller and not
thrive as well as the plants with no overcrowding.
22
MHR TR • Biology 12 Answer Key Unit 5
52. Waste may be classified according to categories of
recyclable, non-recyclable, organic, and toxic because
of the way in which the waste can or cannot be
disposed of an its associated environmental problems.
53. Organisms include zebra mussels, spiny water fleas,
giant hogweed, Asian longhorn beetles, Asian carp, and
purple loosestrife. They can be introduced unintentionally
on vehicles or birds and other migratory animals or
purposefully imported for their beauty. Invasive species
destroy habitat, disturb food webs, introduce parasites
and diseases, and put native species at risk.
54. Snapshots should help to describe the population
and/or population density: a population of over
300 marmots in the mid 1980’s dwindled to 75 by
2001 (25 of which were remaining in the wild). They
should also show the clumped distribution pattern,
since marmots live in small social groups. Life history
may be describe as having a K-selected strategy since
females breed at 3 to 4 years old, have 3 or 4 in a litter,
and are attentive parents.
55. Venn diagrams should include transect, quadrat, and
mark-recapture. Similarities among the three including
that they sample a subset of the population and
require extrapolation of the data to represent the larger
population. Similarities between transect and quadrat
include that they work best on sessile organisms, and
that they calculate population per sampling area.
Differences include low density and large organisms
(transect), high density (quadrat), and high mobility,
and the method of calculation based on recapture
percentages (mark-recapture).
Answers may also mention the method of estimating
the human population which uses a calculation of
tracked births and deaths as well as periodic counting
of every individual.
56. Posters should show a uniform distribution pattern for
a territorial species such as the bald eagle, a clumped
distribution pattern for a species such as trembling
aspen, and a random distribution pattern for a species
such as moose.
57. Sample answer:
Rabbits
Reproductive Strategy
r-strategy
Tortoises
K-strategy
Lifespan
short
long
Litter Size
large
small
Speed of Maturation
fast
slow
Offspring Survival Rate lower
higher
58. Graphs should show an echoed sinusoidal rhythm like
Figure 11.29 on page 524 of the student textbook. An
increase in the rabbit population means that there are
more resources available to foxes, which increases the
fox population. An increase in the fox population leads
to a reduction in rabbits. With a reduction in rabbits,
the fox population does not have as many resources,
so the fox population decreases. With the decrease
in fox population, more rabbits survive, so their
population increases again.
65. Sample answer: Deserts exist where rainforests
once did and aquatic ecosystems contain little life.
Waterways are contaminated and polluted. Crops
normally grown in lower latitudes will grow in higher
latitudes because it is now warm enough there, and
some land is under water due to melted ice caps. Many
species are extinct. Skin cancer affects most people.
Fresh water is extremely costly because it is scarce.
Food is scarce. Fuel is scarce. Disease is rampant due
to waste accumulation. Weather is more extreme.
59. Illustrations should depict a situation in which a nonpoisonous or palatable species looks like one that is
poisonous or unpalatable, such as the monarch and
viceroy butterflies.
66. Scripts should include garbage in oceans that kill
marine life, toxins in plastics that biomagnify when
ingested by marine life, and garbage that fills up
landfills. Solutions should include recycling materials
and purchasing items with a long life or ones that can
be reused or updated.
60. Sample answer: Symbiosis describes the way organisms
live in close relationship with each other. Example
include parasitism—tape worms in the human
intestine which benefit from and harm the human;
mutualism—ants get excess plant sap from aphids
which gain protection from the ants against parasites
and predators, both benefit and neither is harmed;
and commensalisms—barnacles benefit from being
transported to new sources of food when they adhere
to whales, that is not harmed.
61. Diagrams should show a triangle for the rapidly
growing population, a rectangle for the stable
population, and a rhombus that is wider at the top for
the declining population.
62. Sample answer: Biodiversity means having different
kinds of living things in an environment. Biodiverse
environments, like a tropical rain forest, contain a large
variety of animals, plants, and other organisms. Less
biodiverse environments, like deserts, have less variety
or organisms.
63. The main cause is human activity—destruction of
habitat from deforestation, pollution, fires, space taken
by building and agriculture; introduction of invasive
species; overexploitation of fish and other resources, and
degradation of the environment (e.g., climate change).
64. Points may include that less developed countries grow
at a much faster rate than industrialized countries, so it
would be wise to concentrate efforts in less developed
countries. Many of the women in these countries have
few choices outside marriage and children. Therefore,
expanding their opportunities by providing education,
health, family planning, jobs, and other services may
encourage them to have fewer children. It may also
help to reduce child mortality rates so that people do
not feel the need to have more children to ensure the
survival of a sufficient number.
67. Random distribution patterns occur in environments
in which resources are consistent and plentiful. It is
rare in nature for abiotic factors such as soil conditions
and climate to be consistent enough so that members
do not need to cluster or spread apart, and for biotic
factors such as interactions with other individuals to
be neutral.
68. Species that are r-selected become sexually mature early,
produce a large number of offspring, and live close to
their biotic potential. This makes them ideal to begin the
process since a large number of them can grow quickly
to help prepare the habitat for other plants.
69. A development-reproduction trade-off means that
in order to maximize longevity of a species in an
environment, there has to be a trade-off between
investing in long-term development and long life by
producing few offspring and taking care of them to
ensure survival, or short term development and a
shorter life span by producing lots of offspring and
hoping that a few will survive. The two strategies are
dependent to some degree because they both cannot
be pursued to the highest degree at once. The resources
for quick reproduction cannot be used for a system
that lives a long life.
70. Influenza is a density-dependent limiting factor.
Population density is much greater in a school than in
rural areas. Thus, the flu virus spreads more easily from
student to student.
71. Because grizzly bears take so long to mature and have
only a few cubs in their lifetime, new bears cannot be
added quickly to the population. If the population is
at risk, it will take a long time before there are enough
bears in the population to change its status so that they
are no longer at risk.
Biology 12 Answer Key Unit 5 • MHR TR
23
72. a. Mercury is released by burning fossil fuels, mining,
and from substances in industry and agriculture.
b. Mercury enters the waterways and contaminates
organisms in the water. The mercury increases in
concentration as it is passed along the food chain,
affecting top consumers (such as humans) the most.
Mercury harms systems in the body and affects
growth, development, and reproduction.
73. The aphid and the plants have a parasitic relationship,
since the aphid benefits and the plant is harmed. The
aphid and the bacteria have a mutualistic relationship
since both the bacteria and aphid benefits and neither
is harmed.
74. Sample answer: With the increase in population,
the amount of waste humans generate has increased
immensely and thus so has the need for waste
disposal. Since waste does not degrade with speed,
it accumulates. Our landfills are rapidly filling up,
creating environmental problems, incinerating garbage
produces air pollution, and more garbage is spilling
into our oceans, killing marine organisms. The waste
pollutes the environment, spreading diseases, and
presenting a danger to humans and other organisms.
75. The nutrients in the fertilizers could cause algae, plants,
and bacteria to overgrow in the pond. The bacteria use
up oxygen needed by fish and other organisms in the
pond. The algae and other plants could cover the pond,
cutting off the air and light supply. These organisms
could die.
76. Limiting factors include density-dependent factors
such as scarcity of food or space and increase in
diseases or predators, as well as density-independent
factors such as drought, extreme temperatures, and
natural disasters. The density-dependent factors would
increase competition among humans, resulting in a
higher death rate and a lower birth rate than we now
have. The density-independent factors would also
result in a greater death rate and possibly a lower birth
rate. Even if the birth rate remained the same, the
population would slow since the death rate increased.
77. Leaders might look at the proportion of individuals
that are available immediately to work and put money
into the economy, the proportion of current and future
elderly people to support, and the proportion of young
who need education and future jobs, and who will
reproduce to add to the population.
78. These ecosystems can be a source of raw material for
research and production of medicine, food, cosmetics,
and other products; as well as sources for agriculture
and ecotourism. The genetic diversity can be explored
24
MHR TR • Biology 12 Answer Key Unit 5
using biotechnology. If sustainable practices are
used, the people can benefit for a long time without
destroying the ecosystems.
79. Threats to the rainforest include:
Deforestation: The soil in the rainforest gets its
nutrients from the dead leaves and branches.
Deforestation could disrupt this cycle and the soil
may become less fertile and not be able to support as
many species; in turn, other organisms will leave the
area in search of more suitable habitat. In addition,
deforestation would increase leaching, which makes
the soil even less fertile and there will be few plants to
retain the water in the environment. Erosion of the soil
is also a possibility.
Climate change: The area may receive considerably less
rainfall due to climate change. This would accelerate
the desertification of an area already under threat due
to deforestation.
80. Organic pollutants do not degrade in the environment.
Organic pollutants (e.g., DDT) are used in pesticides
or result from burning waste (e.g., dioxin). They
accumulate in the tissues of animals and biomagnify
along the food chain. Organic pollutants can cause
cancer and severe reproductive and developmental
problems, including birth defects.
81. Further urbanization will increase consumption of
natural resources such as fresh drinking water and
land; increase pollution which affects air and water
quality and produces negative health conditions;
increase crowding; and reduce green spaces.
Answers to Unit 5 Self-Assessment Questions
(Student textbook pages 594–5)
1. a
2. d
3. d
4. e
5. d
6. b
7. e
8. e
9. b
10. a
11. Diagrams should show two different species in the
same habitat using different resources within the
habitat, occupying a slightly different ecological niche.
Students should explain that interspecific competition
is between two different species. The two species lessen
competition by resource partitioning—using different
resources in the habitat.
12. One way is to plant a particular species (such as beans)
in one area with adequate resources to use as a control.
Then they may plant the bean plants together with
insufficient resources to demonstrate intraspecific
competition. Finally, they may plant the bean plants
together with another species such as marigold, again
with insufficient resources. Measuring the height, leaf
size, etc. of the bean plants will indicate how well they
grow given competition between the same species
(intraspecific competition), and competition between
the different species (interspecific competition).
13. While Canada is industrialized, with a high standard of
living, Namibia is under-developed, with many living
below the poverty line. Therefore many more resources
are used by the average Canadian, resulting in a much
larger footprint than that of the typical Namibian.
14. The per capita growth rate is -0.7: cgr = ∆N/N
∆N = 8 - 27 = -19 and N = 27. Therefore,
cgr = -19/27 = -0.7037 = -0.7
15. The population is 2275 bees: Dp = N/A and we are
given Dp = 13/m2 and A = 175
Therefore, N = Dp ∆ A = 13 ∆ 175 = 2275 bees.
16. Diagrams should show a triangle for the rapidly
growing population (more young people at the
base), almost a rectangle for the stable population
(even distribution among age groups), and almost an
inverted triangle—wider at the top for the declining
population (more older people and a narrow base of
young people).
a. Population growth would slow as fewer people
of reproductive age worked their way through
the population.
b. A rapidly growing population would have the
greatest proportion of young, who were not
working, but who require a great deal of supplies
and social infrastructure. The economy would likely
boom, although it may struggle to make room in
the labour market as the younger people reach
working age. A stable population likely has a steady
economy as the proportion of working population
remains stable. A declining population likely has the
greatest proportion of retired people who are not
earning, but who require increasing care, supported
by a smaller base of working people, resulting in a
declining economy.
17. Bar graphs should show coal about twice the size of
natural gas, and show renewable sources slightly below
natural gas. The ideal would be 100 percent renewable
sources because burning fossil fuels (coal and natural
gas) pollutes the air, which increases GHGs and toxins
in the environment and can be used up.
18. The researcher waited too long between the first batch
and recapturing the birds. Birds may have migrated
during that time.
19. The population is 100(1 + 0.08)5 = 147 trees.
20. The distribution pattern should be random in summer
and clumped during winter.
21. DDT is easily absorbed into soil and gets into the
waterways where it does not naturally decompose.
It biomagnifies through the food chain, causing lifethreatening deformities in some organisms that are high
on the food chain (e.g., twisted beaks in bald eagles).
22. The statement means that any intrusion into nature has
side effects. For example, cutting down forests changes
weather patterns, and causes loss of diversity and heavy
soil erosion. Pesticide and fertilizer use puts toxins in
waterways, which affects aquatic ecosystems and the
toxins end up in humans.
23. Experiments should discern whether one species
is dangerous and palatable while the other is not
(showing Batesian mimicry); or if both are dangerous/
unpalatable (which indicates Müllerian mimicry).
24. Curves should be J-shaped. Explanations should
indicate that the insects have a large number of
offspring and conditions are ideal for growth during
the summer months. Therefore the population grows
at its biotic potential then. Cooler winter temperatures
limit population growth and kills individuals.
25. The graph shows an exponential increase (population
explosion) for about 25 years, followed by a sharp
decrease (population crash). In the first 25 years, the
island’s deer population grew exponentially due to
the absence of any limiting factors—resources were
plentiful and the deer had no predators. However
the population did not stabilize at carrying capacity.
Instead, it suddenly declined to the point that it was
nearly wiped out in 15 years. It could be inferred
that a sudden change in the habitat wiped out the
population—perhaps the resources on the island were
exhausted by the growing deer population to the extent
that resources did not regenerate enough to support
the deer. Alternatively, perhaps there was a different
limiting factor such as a fire, a flood, or a fatal disease
attacking the population that caused the crash.
Biology 12 Answer Key Unit 5 • MHR TR
25