Download Answers to Mastering Concepts Questions

Answers to Mastering Concepts Questions
19.1
1. Distinguish among ecosystems, communities, and populations.
An ecosystem is all of the communities in an area plus the abiotic environmental
components. A community is all of the populations that live together in one habitat.
Populations are interbreeding individuals of one species living in an area.
2. Which abiotic components influence the distribution of species in the biosphere.
Air, water, temperature, salinity, nutrient availability, and light are examples of abiotic
factors that regulate species distribution.
3. What is the relationship between an organism’s habitat and its niche?
A habitat is where a species lives. A niche is all the resources and conditions a species
requires to survive, grow, and reproduce. The niche includes biotic and abiotic factors.
Habitat is just one facet of a species’ niche.
19.2
1. Explain why average temperature declines with distance from the equator.
Sunlight hits the Earth at an angle as you increase distance from the equator. Because
light intensity is reduced, average temperature decreases.
2. How do prevailing winds, ocean currents, and mountain ranges affect climate?
Prevailing winds move air masses and moisture around the globe. Ocean currents
influence temperature and moisture in coastal regions. Mountain ranges affect climate on
a local scale by causing disruptions in the movement of air and moisture.
19.3
1. How do climate and soil composition determine the characteristics of terrestrial
biomes?
Climate (mostly temperature and precipitation) and soil composition determine which
plants and microorganisms can grow in a particular area. The plants, in turn, influence the
animals and other organisms that live there.
2. List and describe the climate, soils, and inhabitants of each of the major terrestrial
biomes.
 Tropical rain forest: Warm and wet climate; lush, diverse plant and animal life.
 Tropical savanna: Warm year round, with wet and dry seasons; perennial grasses and
patches of fire-resistant trees, with large herds of herbivores and diverse carnivores.
 Desert: Less than 20 cm of rain per year, with cold or hot temperatures; plants are
adapted to little moisture; nocturnal and burrowing animals.
 Temperate deciduous forest: Warm summers, cold winters; deciduous trees are
dominant, with seed- and nut-eating animals and their predators.
 Temperate coniferous forest: Mild winters, cool summers, abundant rain and fog;
evergreen trees dominate the forests, with diverse fishes, amphibians, birds, and
mammals.
 Temperate grassland: Moderate moisture, with hot summers and cold winters;
dominated by grasses and other herbaceous flower plants, along with large herds of
grazing herbivores, prairie chickens, prairie dogs, and coyotes.
 Mediterranean shrubland: Hot, dry summers and mild, moist winters; plants include
shrubby plants with leathery leaves, and animals include jackrabbits, mule deer, and
rodents.
 Taiga: Long, cold winters and a short growing season; spruce, fir, pine and tamarack,
along with caribou, porcupines, red squirrels, snowshoe hares, migratory birds.
 Tundra: Long, cold, dark winters, with short summers; permafrost limits plants to
shallow-rooted shrubs and low-growing perennial herbs; animals include caribou, musk
oxen, reindeer, lemmings, snowy owls, wolverines, and migratory birds.
 Polar ice: Cold, dry, and windy year-round; phytoplankton support the food web, which
also includes microbes, worms, crustaceans, fishes, and mammals.
3. Describe the types of organisms that live in each zone of a lake.
The shallow water along the shoreline houses rooted plants, algae, and cyanobacteria,
along with many kinds of animals, including turtles, frogs, birds, fishes, insects, crayfish,
and spiders. In the photic zone of the open water are phytoplankton and fishes.
Scavengers and decomposers live in deep water and at the lake bottom.
4. How does a river changes from its headwaters to its mouth?
As a river flows from its headwaters it becomes slower-moving, wider, and richer in
sediments and nutrients.
5. Describe some of the adaptations that characterize organisms in the open ocean,
estuaries, intertidal zones, and coral reefs.
Floating phytoplankton carry out photosynthesis in the photic zone of the open ocean.
Consumers either scoop up the plankton near the surface, catch the larger animals, or rely
on dead material that falls toward the ocean floor. Organisms living in estuaries must
cope with the daily tides, which bring extreme changes in salinity and moisture. Intertidal
organisms have adaptations that allow them to withstand daily periods of extreme
dryness, wetness, heat, and cold, along with protection against wave action. Coral reef
organisms have adaptations that allow them to live in the nooks and crannies of the reef.
19.4
1. What is the competitive exclusion principle?
The competitive exclusion principle states that two species cannot coexist indefinitely in
the exact same niche; sooner or later, the one with the greater reproductive rate will
replace the other.
2. List three examples of symbiotic relationships.
Three examples of symbiotic relationships include mutualistic relationships between
algae and coral animals, mycorrhizal fungi in plant roots, and humans and the bacteria
that live in their guts; commensal relationships such as moss living on tree bark; and
parasitic relationships such as ticks, fleas, and lice and the animals on which they feed.
3. Describe some adaptations that protect against herbivory and predation.
Thorns, milky sap, and poisonous or distasteful chemicals are protections against
herbivory; camouflage, warning coloration, weapons, and defensive behaviors are
protection against predation.
4. Define coevolution and describe an example.
In coevolution, two species influence each other’s evolution and subsequent adaptations.
An example is the relationship between a flowering plant and its pollinator.
5. How are keystone species important in communities?
Keystone species are important in communities because they make up a small proportion
of the community’s biomass, yet they disproportionately affect species diversity.
19.5
1. How do ecologists measure species diversity in a community?
One way is through species richness; the total number of species in a habitat. Another
method is relative abundance, which describes the proportion of the community that each
species represents.
2. What is succession?
Succession is a change in the species that make up a community.
3. Distinguish between primary and secondary succession.
Primary succession begins in a pristine habitat with no previous communities, and
secondary succession occurs in communities that are disturbed but not destroyed.
4. What processes contribute to primary and secondary succession?
Primary succession begins with the emergence of a new habitat; secondary succession
begins with disturbance to an existing community. In both cases, pioneer species are the
first to arrive. These species change the environment in ways that permit other species to
thrive. In theory, the community continues to change until a stable climax community is
in place.
5. How do disturbances prevent true climax communities from developing?
Pockets of local disturbance create patches in different successional stages throughout the
habitat. These disturbances (fires, trees falling, storm damage) happen frequently enough
to prevent a true climax community.
6. How does succession occur as a lake becomes a wetland?
New lakes lack nutrients and support little algal growth. As more nutrients are added
through sedimentation, productivity increases. As the lake continues to accumulate
sediment it becomes filled in to the point where it becomes a wetland with saturated soils
for at least a portion of the year. Wetlands host different plant and species from lakes.
19.6
1. Identify the trophic levels in a food chain.
Primary producers are plants and other autotrophs that can produce their own organic
matter. Primary consumers eat primary producers, secondary consumers eat primary
consumers, and tertiary consumers eat secondary consumers. Decomposers eat dead
organisms and organic wastes.
2. What roles do primary producers and decomposers play in ecosystems?
Primary producers use inorganic nutrients to create the organic material an ecosystem
needs, and decomposers recycle the inorganic nutrients to the ecosystem as they decay
organic matter.
3. How efficient is energy transfer between trophic levels in food webs?
In general, about 2% to 30% of the energy available to a trophic level is fixed into tissue
and made available to the next higher trophic level. (The “10% rule” assumes an average
of 10%.) The rest is lost as heat.
4. Draw an energy pyramid for an ecosystem with three levels of consumers.
Answers may vary, but the pyramid might include producers (100 kcal), primary
consumers (10 kcal), secondary consumers (1 kcal), and tertiary consumers (0.1 kcal).
5. Explain how biomagnification affects organisms at the top of a food chain.
Biomagnified chemicals are stored in fatty tissues and are not biodegradable. All of the
molecules present in each trophic level are, therefore, concentrated into the much smaller
biomass that makes up the next highest level. Top consumers, therefore, acquire the
highest concentrations in their tissues.
19.7
1. What features do biogeochemical cycles share?
The elements in all biogeochemical cycles are stored in one of four reservoirs: organisms,
atmosphere, water, and soil/rock. The elements are transferred among all four reservoirs
and transformed in the process.
2. Describe the steps of the water, carbon, nitrogen, and phosphorus cycles.
 Water cycle: In the atmosphere, condensation of water vapor causes precipitation that
falls to Earth. The water may then evaporate and return to the atmosphere, or it may run
off from land surfaces into bodies of water. Some rain water enters groundwater, which
eventually returns to the land surface.
 Carbon cycle: CO2 from the atmosphere is incorporated into tissues of autotrophs. Their
tissues are consumed by multiple levels of consumers and, eventually, by decomposers.
Meanwhile, both autotrophs and heterotrophs respire, returning CO2 to the atmosphere.
Burning fossil fuels and wood also returns CO2 to the atmosphere. CO2 in the
atmosphere may also dissolve into oceans and become part of ocean sediments.
 Nitrogen cycle: Nitrogen-fixing bacteria transform N2 into ammonium, and lightning
transforms N2 into nitrates. Plants incorporate ammonium and nitrate into organic
molecules, which enter food chains and are passed up trophic levels. Decomposers
release ammonium ions as they decompose organic wastes and the remains of animals
and plants. Nitrifying bacteria transform the ammonium into nitrates and nitrites, which
denitrifying bacteria transform into N2.
 Phosphorus cycle: Rock that contains phosphorus erodes. Plants absorb the phosphorus,
which subsequently passes up food chains. Decomposers return the inorganic
phosphorus to soil. Some phosphates enter waterways and become deposited in new
sediments that eventually form new layers of rock.
3. Describe how a terrestrial ecosystem can interact with a faraway aquatic ecosystem.
A terrestrial ecosystem can interact with a faraway aquatic ecosystem through the action
of the atmosphere, through circulation of ocean currents, and through runoff from land to
water. In some cases, migratory animals can carry nutrients from the land to the ocean
and back.
19.8
1. Describe the relationships among the grass, fungus, and virus.
The virus infects the cells of the fungus, which, in turn, infects the grass. The grassfungus-virus relationship allows for all three species to colonize warm habitats that they
could not otherwise occupy.
2. List the benefits and drawbacks of inoculating all of our food crop plants with the
fungus–virus team. What would you need to know before recommending that strategy?
A potential benefit is that food crop plants might better withstand heat stress, possibly
increasing yields. A potential drawback is that the fungus-virus team may cause disease
in the plant, reducing yields; alternatively, the fungus and virus might not be compatible
with crop plants at all. To determine whether to inoculate a plant, you would need to
investigate the host range of the fungus-virus team, measure crop yields under various
conditions, and determine whether inoculated crops might harm humans or the
environment in unintended ways.
Answers to Write It Out Questions
1. How does a community differ from an ecosystem?
A community is a group of interacting populations that inhabit the same region. An
ecosystem includes a community plus the nonliving environment within a defined area.
2. How does a habitat differ from a niche? Describe your own habitat and niche.
A habitat is a physical place where members of a population typically live. A niche is all
the resources a species exploits for its survival, growth, and reproduction. My habitat is
my home and the other physical locations where I spend time; my niche includes the
habitat plus the food I eat, the water and air I breathe, the other resources I exploit, and
the job I do.
3. How does the fact that Earth is a sphere tilted on its axis influence the distribution of
life?
The fact that Earth is a sphere tilted on its axis affects a region’s sunlight, temperature,
and moisture, which are major determinants of climates. Solar energy is most intense at
the equator, where the sun is directly overhead. The average temperature falls with
distance from the equator because the same amount of solar energy is distributed over a
larger area. Earth’s major convection cells, composed of rising and falling air masses,
mean that moisture availability also varies worldwide.
4. List adaptations that characterize organisms in each of the following biomes: tropical
rain forest, savanna, temperate grassland, tundra, desert, taiga, the rocky intertidal zone,
the bottom of a lake.
- The tropical rain forest has a constantly warm and moist climate that favors plant
growth year-round. Plants in the rainforest are adapted to high moisture levels and poor
soils.
- In a savanna, the weather is warm year-round, with distinct wet and dry seasons. Fire
plays a role in the savanna ecosystem, so plants are fire-resistant.
- Temperate grasslands have deep, rich soils that support extensive growth of grasses, but
annual rainfall is insufficient to support trees. Grasses resprout from their bases, an
adaptation to both grazing and fire.
- In the tundra, soils are rich in organic matter, but shallow. Only plants that tolerate cold
winters and have shallow root systems grow in the tundra.
- Deserts are dry; desert plants have adaptations that enable them to store water.
- The taiga is cold and snowy, with scarce moisture and a short growing season. Plant
roots have adaptations to acidic, nutrient-poor soils.
- The rocky intertidal zone is alternately exposed and covered by water. Organisms that
live there have adaptations that enable them to hold tightly to their substrates.
- The bottom of a deep lake has no light penetration; the inhabitants are scavengers and
decomposers that can detect food by scent, not sight.
5. Suppose you are exploring the chaparral ecosystem in California. You encounter a
shrub species that you think may be fire-adapted, and you wonder whether the plant can
reproduce in the absence of fire. Design an experiment that would help answer your
question.
One way to answer the question would be to set aside a plot of chaparral from which fire
was excluded. You could then take seeds from the shrub and plant them in the fireprotected plot. Observe the plants over time to see whether they can complete their life
cycles in the absence of fire.
6. Describe how and why photosynthetic activity differs in each region of a lake or ocean.
Because light penetrates water to different degrees at different depths, photosynthetic
activity is highest near the surface and declines with depth. In both lakes and the ocean,
the photic zone is the only area where photosynthesis can occur. Photosynthetic rates are
generally highest near the shore, where nutrients are most abundant.
7. Nuisance aquatic plants such as hydrilla can disrupt the ecology of a lake. Two of the
most common ways to control nuisance aquatic plants are herbicides (chemicals that kill
plants) and biological control (introducing fungi or animals that consume the plants).
How might each strategy help or harm the lake ecosystem?
The herbicides could help by reducing the plant before it chokes out resources; however,
it may also kill beneficial plants, disrupting the food sources of other organisms.
Biological controls could also reduce the nuisance plant without introducing toxins.
However, the introduced organisms could begin killing desirable plants, or they may
themselves become a nuisance.
8. How can two species share the same habitat without one driving the other to
extinction?
Two species can share the same habitat if they use a different subset of the available
resources (i.e., they have different niches).
9. Describe and give examples of three types of symbiotic relationships.
In a symbiotic relationship, one species lives in or on another. Three types include
mutualism, commensalism, and parasitism. Both partners benefit from a mutualistic
relationship; an example is a cow plus the cellulose-digesting microbes in its rumen. In
commensalism, one partner benefits and the other neither benefits nor is harmed by the
relationship; an example is the tiny mites that live, eat, and breed in a human’s hair
follicles. In parasitism, one partner benefits and the other is harmed. A tree that has
mistletoe growing on it illustrates parasitism because the mistletoe lives on water and
nutrients that the tree has acquired.
10. List examples of adaptations that enable an organism to compete with other species,
live inside another species, find food, and avoid herbivory or predation. How does each
adaptation contribute to the organism’s fitness?
An example of an adaptation that enables an organism to compete is the rapid growth of a
seedling, which may shade out others as it acquires light energy. More photosynthesis
means more energy for reproduction. An adaptation that enables an organism to live
inside another is the suckers on the head of a tapeworm, which keep the worm from being
flushed out of an animal’s digestive tract. A worm with suckers acquires more food than
one without, which means more energy is available for reproduction. An example of an
adaptation that helps an animal find food is an eagle’s keen eyesight. An eagle that can
spot small animals from above acquires more food than one with poor eyesight. An
example of an adaptation that helps an organism avoid predation is camouflage. An
animal that can avoid being eaten (at least before reproductive age) has a chance at
reproductive success.
11. What is a keystone species? How do researchers design experiments that help them
identify keystone species?
Keystone species greatly influence species diversity, even though their biomass makes up
only a small proportion of the community. One mechanism to identify keystone species
is to remove one species at a time and monitor the effects on diversity.
12. Distinguish between primary and secondary succession.
Primary succession occurs where no other ecosystem has occurred before, such as on a
cooled lava flow from a volcanic eruption. Secondary succession occurs when one
ecosystem is removed and another forms in its place, such as when a forest is clear cut,
farmed for an extended period of time and then left to grow.
13. How is natural selection apparent in ecological succession?
Succession is a change in species composition over time, and it occurs because one set of
species alters the environmental conditions in such a way that other species can begin to
exploit the habitat. In changing the conditions, they are altering the selective forces that
determine whether or not an organism can survive and reproduce in the habitat.
14. How are decomposers and autotrophs essential to ecosystem function?
The autotrophs use light energy and inorganic nutrients to produce organic molecules.
The decomposers break down the organisms and release inorganic nutrients back into the
soil.
15. In the United States, people have reduced or eliminated the populations of top
predators such as wolves and coyotes. How might this history relate to the recent
explosion of deer populations? Using the ecological principles you have learned in this
unit, what are some possible ways to reduce deer populations? What are the pros and
cons of each approach?
Without the top predators, death rates in deer populations declined, leading to an increase
in population size. To reduce the population you could increase death rates by controlled
hunting, or you could decrease birth rates with birth control or sterilization measures.
Hunting puts humans in the role of top predator and this re-establishes a balance. Unlike
wolves, however, humans do not cull the sick and old deer. Instead, they attempt to
remove the prime specimens, which could alter the gene pool of the population.
Sterilization or birth control methods are awkward, time-consuming, and expensive.
16. How do organisms return water, carbon, nitrogen, and phosphorus to the abiotic
environment?
Plants absorb water from the soil and release through transpiration. Animals and humans
drink water and consume it, returning it to the environment through evaporation and
urination. Respiration returns C to the atmosphere, and N returns to the environment in
metabolic wastes. In addition, all organisms return C, N, and P to the abiotic
environment when they die and are decomposed.
17. Several sites on the Internet offer water- or carbon-footprint calculators. Use one to
compute your footprints. What assumptions go into these calculations? What strategies
could you use to reduce either footprint?
Calculations of carbon and water footprints are based on measures of home energy and
water use, travel, diet, shopping, and recycling habits. Both footprints are estimates based
on average lifestyles and behaviors. Some strategies to reduce your carbon footprint
include reusing materials, biking or walking, buying locally, bringing your own bags to
the grocery store, and adjusting your thermostat to save energy. Some strategies to
reduce your water footprint include reducing water use in the home and yard, eating less
meat, and purchasing less stuff.
18. Review the structures of organic molecules in chapter 2. How do the molecules in
living cells create interconnections between the carbon, nitrogen, and phosphorus cycles?
Carbon is part of all organic molecules, while nitrogen occurs in proteins and nucleic
acids, and phosphorus occurs in nucleic acids, ATP, and phospholipids. Molecules that
contain combinations of C, N, and/or P represent intersections of the nutrient cycles.
Answers to Pull it Together Questions
1. What factors determine the location of each biome on Earth?
For terrestrial biomes, temperature, moisture, soil characteristics, altitude, distance from
the oceans, and latitude are important factors. For aquatic biomes, distance from shore,
light penetration, depth/pressure, latitude, nutrient availability, current strength, and
salinity are important.
2. What types of forests occur on Earth, and what combination of conditions favors each
type?
The main types of forests are rainforests, temperature deciduous forests, temperate
coniferous forests, and taiga. High rainfall and warm temperatures throughout the year
favor the rainforest. In temperate deciduous forests, rainfall is evenly distributed
throughout the year; summers are warm, and winters are cold. Temperate coniferous
forests usually grow where winters are milder and summers are cooler. Taiga occurs
where winters are very long and cold.
3. List examples of coastal ecosystems.
Examples of coastal ecosystems include estuaries, intertidal zones, and coral reefs.
Estuaries are where fresh water from rivers meets ocean water, resulting in brackish
water and currents that sustain all sorts of unique organisms. Intertidal zones describe the
areas of the shore that are alternately submerged and exposed with the tide. Coral reefs
form in warm shallow waters along tropical shorelines.
4. List some components of your abiotic environment.
[Answers will vary.]
5. Where do mutualism, commensalism, and parasitism fit into this concept map?
"Symbiosis" connects with the phrase "may benefit both participants, which is a" to
"Mutualism". "Symbiosis" connects with the phrase "may benefit one participant and be
neutral to the other, which is a" to "Commensalism". "Symbiosis" connects with the
phrase "may benefit one participant and harm the other, which is a" to "Parasitism".
6. Where do primary, secondary, and tertiary consumers fit into this concept map?
"Herbivory/predation" connects with the phrase "includes" to "Tertiary consumers"
which connects with the phrase "prey on" to "Secondary consumers" which connects with
the phrase "prey on" to "Primary consumers".