Deck 44: Ecological Communities

Question 1

As the volcanic island of Krakatau was repopulated,which types of species would most likely have been the last to colonize the island?

A) Animal-dispersed plants
B) Fruit-eating bats and birds
C) Plant species requiring high light levels
D) Plant species requiring low light levels
E) Wind- and water-borne seeds and spores

Answer 1

A

Question 2

Which statement best describes the changes in the biological community of Krakatau since the volcanic eruption?

A) Recolonization has been slow and incomplete.
B) Most colonizers have arrived by water rather than wind.
C) The thick layer of ash prevented forests from becoming reestablished.
D) After a century,the island has been repopulated,but species diversity is low.
E) After a century,the island has recovered and species composition is dynamic.

Answer 2

E

Question 3

Mountaintop plant communities in central and northern Europe are becoming more species-rich as the warming climate allows lower-altitude plants to move up toward the peaks.If this trend continues,the most likely outcome will be that

A) increasing richness eventually will lower overall community productivity.
B) all species will evolve by partitioning their niches so that a lower but stable diversity level can be maintained.
C) increasing richness will increase competition,which could eliminate some original mountain peak species.
D) one of the new arrivals will eventually drive out all the others,resulting in virtual monocultures on the peaks.
E) the original mountaintop species will move down the mountainsides,increasing the homogeneity of the mountain's plant communities.

Answer 3

C

Question 4

When a species attempts to colonize a new area,all of these factors except _______ is likely to result in its local extinction.

A) excessive predation
B) excessive competition
C) severe drought conditions
D) lack of an essential resource
E) a climate similar to its previous climate

Question 5

A large flowerbed is designed to attract pollinators such as bees,butterflies,and hummingbirds.It contains a variety of plants of different heights-shrubs,forbs,and annuals-with flowers that bloom at different seasons.The pollinators are most likely attracted to the flowerbed because of its complex

A) species turnover.
B) habitat structure.
C) successional changes.
D) ecological transitions.
E) environmental gradient.

Question 6

Which beetle(s)would most likely be found in recently deposited dung?

A) Beetle A only
B) Beetle B only
C) Beetle C only
D) Beetles A and B
E) Beetles B and C

Question 7

An ecologist who runs a transect across a gradient from serpentine soils to non-serpentine soils will most likely find

A) a trophic cascade.
B) a change in species composition.
C) tall trees only on non-serpentine soils.
D) the same habitat structure on each side.
E) support for the theory of island biogeography.

Question 8

A forensic entomologist can date an organism's time of death according to the species of insects found on or near the body.This scientist is applying knowledge about the process of

A) extinction.
B) succession.
C) trophic cascades.
D) island biogeography.
E) community structure.

Question 9

For study purposes,which of the following would not be considered an ecological community?

A) The finches of the Galápagos Islands
B) All species found within one specific acre of a forest
C) The grazing herbivores in the prairie
D) The aquatic plant species of a pond
E) The population of one finch species of the Galápagos Islands

Question 10

Which group is the best example of an ecological community?

A) All animals in a local grassland
B) All field mice in a local grassland
C) All living organisms in all grasslands
D) All living organisms in a local grassland
E) All living organisms and abiotic factors in a local grassland

Question 11

On Krakatau,the tallest trees are most likely to be found

A) along the beaches.
B) on gentle inland slopes.
C) at or near the summit.
D) scattered over the whole island.
E) exposed to the highest winds.

Question 12

As climate change continues,average temperatures are increasing at all latitudes and spring is beginning two to three weeks earlier in many areas.How will these changes likely affect plant communities?

A) Most species will go extinct.
B) Most species will survive but be very unhealthy.
C) Most species will adapt to the changes and persist at lower populations.
D) The most heat-tolerant species will take over,lowering species diversity.
E) Some species may go extinct,but many will shift their ranges northward.

Question 13

The volcanic island of Krakatau provides a very good illustration of

A) ecological efficiency.
B) the implementation of restoration ecology.
C) how communities reassemble after a disaster.
D) the relationship between productivity and disturbance.
E) the relationship between productivity and species richness.

Question 14

Which ecological studies have documented the effects of climate change on communities?

A) Studies of the effects of wolves on aspens
B) Observations from Krakatau
C) Observations of rodent middens
D) Studies of island biogeography
E) Tillman's experiments on productivity and species richness

Question 15

A large lake in a relatively isolated environment has had clear water and a stable,moderately diverse species composition for hundreds of years.When the region is developed into farmland,the lake begins receiving large amounts of fertilizer runoff,making it turbid and highly eutrophic (excessively rich in nutrients).The species composition becomes much less diverse and is made up of species that tolerate low oxygen.Even after the farmland is abandoned and fertilization stops,the lake remains eutrophic.This is an example of a(n)

A) disturbance.
B) ecological transition.
C) successional change.
D) environmental gradient.
E) change in habitat structure.

Question 16

The process by which the beetle community changes over the hours and days after the deposition of dung is called

A) disturbance.
B) habitat structuring.
C) a trophic cascade.
D) succession.
E) ecological transition.

Question 17

A community ecologist would most likely study

A) nutrient flow through an ecosystem.
B) population growth of a single species.
C) interactions among individuals of the same species living in a small area.
D) interactions among individuals of different species living in a small area.
E) the cycling of matter through biotic and abiotic components of a geographical area.

Question 18

After a major ice storm,most trees in an area fall and die.Over the course of two decades,a new community reassembles there.The ice storm would be considered a(n)

A) extinction.
B) disturbance.
C) trophic cascade.
D) climate change.
E) ecological transition.

Question 19

An ecologist is studying changes in the abundance of plant species in a marsh as one moves away from the ocean.This means the ecologist is studying species changes that occur along a(n)

A) transect.
B) corridor.
C) trophic cascade.
D) successional gradient.
E) environmental gradient.

Question 20

Which characteristic is not associated with high-intensity methods of coffee growing?

A) Greater yield
B) More pollution
C) Increased biodiversity
D) High cost of chemicals
E) High-density plantations

Question 21

Grain is eaten by cows,and cows are eaten by humans.If the ecological transfer efficiency between each trophic level is 10 percent,how much grain is required to produce 70 kg of human biomass?

A) 7 kg
B) 70 kg
C) 700 kg
D) 7,000 kg
E) 70,000 kg

Question 22

If gross primary productivity (GPP)is 120 units per day,and the respiration rate (R)of primary producers is 30 units per day,net primary productivity (NPP)is _______ units per day.[Note: Use the formula NPP = GPP - R.]

A) 4
B) 30
C) 90
D) 120
E) 150

Question 23

In a microbial community,autotrophs generate 1,000 calories per hour of GPP and 500 calories per hour of NPP.Primary consumers convert 60 calories per hour into their own biomass.What is the ecological efficiency in the link between autotrophs and primary consumers in this community?

A) 4 percent
B) 6 percent
C) 10 percent
D) 12 percent
E) 16 percent

Question 24

Net primary productivity (NPP)of a community is approximately equivalent to

A) gross primary productivity (GPP).
B) energy used in respiration per unit time.
C) change in biomass of primary producers per unit time.
D) energy captured by plants from sunlight per unit time.
E) gross primary productivity (GPP)plus respiration (R).

Question 25

The notion of species diversity incorporates which factor(s)?

A) Species richness only
B) Species evenness only
C) Total number of individuals only
D) Species richness and species evenness
E) Species richness and total number of individuals

Question 26

What is the most likely reason that the curve in the top graph mostly levels off between five and ten species?

A) The prairie community only has five to ten niches.
B) The community is approaching its maximum productivity,given the resources available.
C) With more than 10 species,competition prevents further productivity.
D) With more than 10 species,species diversity no longer influences productivity.
E) The additional species must be smaller and therefore contribute less to the biomass.

Question 27

Three plant communities have the species composition shown in the table below.Which community or communities have the highest species evenness?

A) Community A only
B) Community B only
C) Community C only
D) Communities A and B only
E) The three communities have equal species evenness.

Question 28

Each species has a particular niche within a community.This niche is defined by which two sets of factors?

A) Functional role and net primary productivity
B) Physical environment and biological environment
C) Net primary productivity and physical environment
D) Net primary productivity and biological environment
E) Physical and biological environment and functional role

Question 29

The loss of a single species from a community will most often affect community function by affecting the community's

A) growth rate.
B) trophic interactions.
C) physical environment.
D) ecological efficiency.
E) gross primary productivity.

Question 30

In the total of Earth's food webs,the sun represents

A) the major source of energy.
B) the only source of energy.
C) the primary producer.
D) a biotic factor not affecting food webs.
E) an abiotic factor not affecting food webs.

Question 31

Three plant communities have the species compositions shown in the table below.Which community or communities have the highest species richness?

A) Community A only
B) Community B only
C) Community C only
D) Communities A and B only
E) Communities A,B,and C

Question 32

The number of trophic levels in communities is limited by

A) predation.
B) succession.
C) competitive exclusion.
D) the presence of decomposers.
E) the loss of energy between trophic levels.

Question 33

A grassland is composed primarily of a single type of grass,with small amounts of three other grasses and several forbs.How will this species composition be likely to affect the function of this community?

A) All species will have an approximately equal effect on function.
B) The dominant grass will mostly define the function of the community.
C) The forbs will have the greatest effect on function because they are unique.
D) All grasses will have an approximately equal effect on function;forbs will have a lesser effect.
E) The species having the greatest effect on function may vary,depending on the abiotic environment.

Question 34

A common way to measure community function is to measure

A) metabolism of selected species in the community.
B) metabolism of selected individuals in the community.
C) total amount of biomass at the end of the growing season.
D) total biomass of major species at the end of the growing season.
E) flux,or flow rate of energy between community and environment.

Question 35

Bumblebees live in nests in loose soil on the ground,in areas with little vegetation.However,they must be near vegetated areas,where they feed on and pollinate many flowering plants.This information describes the bumblebee's

A) niche.
B) energy source.
C) method of dispersal.
D) ecological efficiency.
E) community structure.

Question 36

Use the following to answer questions :
Refer to the graphs below showing data from the studies of David Tilman and colleagues on the effect of species diversity on net primary productivity in prairie ecosystems.
Based on the data in the two graphs,how can the effects of species richness and number of functional groups (niches)on NPP best be described?

A) Increased number of niches,which is tied to increased species richness,has a major effect on increasing NPP.
B) Increased species richness has less effect on increasing NPP than increased number of niches does.
C) Increased number of niches is responsible for the total effect of increased species diversity on NPP.
D) Increased species richness is responsible for the total effect of increased species diversity on NPP.
E) Increased number of niches and increased species richness independently increase NPP.

Question 37

Under stress,a community loses a number of species.When the stress is removed,the species composition recovers and then stabilizes.During this process,what will be the most likely effect on net primary productivity?

A) It will increase.
B) It will decrease.
C) It will be unaffected.
D) It will increase and then stabilize.
E) It will decrease,recover,and then stabilize.

Question 38

Suppose that plants are able to convert 80 percent of the energy that they obtain into biomass,and that the ecological efficiency of primary consumers is 20 percent.For every calorie that is converted into primary consumer biomass,how much energy must be captured and converted into chemical energy?

A) 1.25 calories
B) 5 calories
C) 6.25 calories
D) 25 calories
E) 100 calories

Question 39

All of these factors reduce the efficiency of energy transfer between trophic levels except

A) heat loss due to maintaining homeostasis.
B) heat loss due to metabolism.
C) indigestibility of some biomass.
D) biomass stored as fat or starch.
E) lack of availability of some biomass.

Question 40

Earth could support a larger human population if more people

A) became vegetarians.
B) became omnivores.
C) became carnivores.
D) hunted their own food.
E) metabolized more of the energy they consume.

Question 41

Species richness results in increased numbers of functional groups,or niches,in a community,because having more species

A) increases the likelihood of predation within the community.
B) increases the likelihood of competition within the community.
C) increases the likelihood of groups of species having complementary niches.
D) decreases the likelihood of predation by providing species with more places to hide.
E) decreases the likelihood of competition by "evening out" the abundance of each species.

Question 42

According to the theory of island biogeography,if the colonization rate is equal to the extinction rate,the species richness is

A) low.
B) high.
C) increasing.
D) decreasing.
E) at equilibrium.

Question 43

Which factor is not likely to be very important in determining species diversity?

A) Habitat structure
B) Climatic conditions
C) Net primary productivity
D) Occasional seasonal storms
E) Large-scale disturbances,such as glaciation

Question 44

Niche complementarity is most closely related to which ecological community function?

A) Resource partitioning
B) Trophic cascades
C) Mutualism
D) Habitat fragmentation
E) Intraspecific competition

Question 45

Suppose that in a study of an ecological community,NPP increases as species richness increases,but scientists find no relationship between NPP and the number of functional roles played by the species.Which conclusion could be inferred?

A) Ecological efficiency of the community is high.
B) Ecological efficiency of the community is low.
C) Tilman and his colleagues drew the wrong conclusions from their study of prairie communities.
D) Niche complementarity does not explain the richness-productivity relationship in this community.
E) Niche complementarity explains much of the richness-productivity relationship in this community.

Question 46

What is one hypothesis biologists have proposed to explain latitudinal gradients in species richness?

A) Intense predation in polar regions limits the number of species.
B) Lack of pathogenic organisms in the tropics promotes species richness.
C) Lack of mutualistic interactions at higher latitudes limits the number of species.
D) Presence of extensive mountain ranges and coastlines at higher latitudes limits species richness.
E) Greater energy flow in the tropics has led to narrower,more specialized niches and thus promoted species diversity.

Question 47

In the prairie community studies by Tilman and colleagues,two hypotheses were proposed to explain the increase in NPP as species richness increased.One involved accidental sampling,in which samples by chance included one or more "superspecies" that had a disproportionate effect on community function.Which other explanation did Tilman and his colleagues decide was more reasonable?

A) Niche complementarity,leading to more efficient resource use
B) Niche complementarity,leading to increased reproductive rates
C) Changes in microclimate,leading to increased reproductive rates
D) Decreased species evenness,leading to a few species influencing community function
E) Increased species evenness,leading to all species equally influencing community function

Question 48

Biome A supports approximately 1,400 species of birds,biome B supports approximately 105 species,and biome C supports 56 species.Based on these numbers,what are the likely climates of these biomes?

A) A = tropical;B = tundra;C = temperate
B) A = tropical;B = temperate;C = tundra
C) A = temperate;B = tropical;C = tundra
D) A = temperate;B = tundra;C = tropical
E) A = tundra;B = temperate;C = tropical

Question 49

The first naturalist to observe and remark on the relationship between species richness and latitude was

A) David Tilman.
B) Charles Darwin.
C) Edward O.Wilson.
D) Alfred Russel Wallace.
E) Alexander von Humboldt.

Question 50

Latitudinal gradients in species diversity exist in marine as well as terrestrial habitats.Which ocean community would most likely have the highest species diversity?

A) Fjord off the coast of Norway
B) Coral reef in the equatorial Pacific
C) Estuary off Newfoundland,Canada
D) Estuary off the South Carolina coast
E) Kelp bed off the northern California coast

Question 51

Which pair of scientists is most associated with the theory of island biogeography?

A) David Tilman and Craig Venter
B) Charles Darwin and Alfred Russel Wallace
C) Edward O.Wilson and Robert MacArthur
D) James Watson and Daniel S.Simberloff
E) Alexander von Humboldt and Louis Agassiz

Question 52

More than a thousand species of frogs live in the Amazon rainforest.They live in varied habitats,from the forest floor to the highest levels of the canopy.In this situation,the factor that most likely is having a direct effect on species diversity is

A) climate.
B) predation.
C) colonization.
D) habitat structure.
E) habitat fragmentation.

Question 53

According to the island biogeography model,which two factors primarily determine the number of species on an island?

A) Climate and size of island
B) Species pool and speciation rate
C) Speciation rate and extinction rate
D) Species evenness and habitat structure
E) Size of island and distance from mainland

Question 54

Refer to the table below.Fauna groups A-D are populating an island.They have the dispersal abilities shown,and they are either strongly affected or little affected by similar species already present on the island.If strongly affected,their extinction rate rises;if not strongly affected,extinction rate does not change.Which group of fauna would most likely maintain the largest number of species on the island,assuming all other factors are equal?

A) Fauna group A
B) Fauna group B
C) Fauna group C
D) Fauna group D
E) All fauna groups equally

Question 55

Daniel Simberloff and Edward O.Wilson tested the theory of island biogeography by first removing all arthropods from a group of mangrove islands and then measuring the recolonization of the islands over a two-year period.Which result did they not observe?

A) Species number rapidly increased at first,and then leveled off.
B) After two years,all islands had similar levels of species richness.
C) Recolonization rates were fastest for islands closest to the mainland.
D) After the first year,the number of species on each island changed relatively little.
E) After two years,each island had approximately the same number of species as it did originally.

Question 56

Long-term stable climatic conditions in tropical regions are often cited as one reason for high species diversity at these low latitudes.Which of the following consequences of a more stable climate has not been proposed as a likely mechanism explaining increased species diversity in the tropics?

A) Lower extinction rates
B) Increased time for niche specialization
C) Higher NPP
D) Lower rates of predation and parasitism,allowing primary producers and herbivores to flourish
E) Lack of large-scale disturbances such as glaciation,allowing time for speciation

Question 57

Which of these habitats has the highest species richness?

A) Tropics
B) Northern temperate zone
C) Southern temperate zone
D) Sub-tropics of both hemispheres
E) Temperate zones of both hemispheres

Question 58

One possible reason for the increase in species richness toward the tropical latitudes is that

A) net primary productivity is lower in the tropics than in temperate climates.
B) large-scale disturbances are more prevalent in the tropics than in temperate climates.
C) small-scale disturbances are more prevalent in the tropics than in temperate climates.
D) tropical climates are less variable than temperate climates.
E) tropical climates are more variable than temperate climates.

Question 59

The theory of island biogeography is most concerned with the

A) relationships between species diversity and area.
B) latitudinal gradient of species richness.
C) effects of human colonization on diversity.
D) diversity on volcanic versus coral reef islands.
E) evolution of endemic species.

Question 60

According to the theory of island biogeography,which type of island would have the highest species diversity?

A) A large island near the mainland
B) A small island near the mainland
C) A small island far from the mainland
D) A large island far from the mainland
E) An island of any size near the mainland

Question 61

When New York City needed to meet national water quality standards,they chose to invest $1.5 billion in protecting land and upgrading sewage systems in the Catskills (the source of their water)rather than spending $6-$8 billion on a new waste treatment facility in the city.This choice resulted in benefits in both New York City and the Catskills that included all of these except

A) saving money.
B) decreasing pollution.
C) improving water filtration.
D) improving sewage treatment.
E) replacing a natural with a technological system.

Question 62

Why is it important to place a value on ecosystem services?

A) To enable cities and businesses to charge for them
B) To insure that they are delivered to those who need them
C) To insure that their value is recognized and they are protected
D) To make it easier to transform them into technological services
E) To insure that they are used only for human,not natural,purposes

Question 63

Corridors help mitigate the effect of habitat fragmentation because they

A) increase NPP.
B) enhance the quality of habitat.
C) increase ecological efficiency.
D) lower the likelihood of interspecific competition.
E) increase the probability of migration between patches.

Question 64

Which of the following would not be considered an example of an ecosystem good or service?

A) Forests removing excess carbon dioxide from the atmosphere
B) Bees pollinating an invasive weed species
C) Bacteria metabolizing a substance that poses a health threat to humans or cattle
D) Blowflies limiting the population growth of an insect pest species
E) Marsh grasses limiting the effects of storm surges from hurricanes

Question 65

Until the mid-1960s,dung from introduced cattle accumulated in Australia because

A) Australia lacks native dung beetle species.
B) cattle dung poisoned the native dung beetle species.
C) native dung beetles were adapted to dung that is drier than cattle dung.
D) native dung beetles were adapted to dung that is wetter than cattle dung.
E) native dung beetles were unable to process nitrogen-containing materials.

Question 66

Biologists working to improve the functioning of a highly disturbed aquatic community are engaged in the practice of _______ ecology.

A) natural
B) restoration
C) succession
D) sustainable
E) experimental

Question 67

Habitat fragmentation leads to decreased species richness for all of these reasons except that

A) the total amount of habitat decreases.
B) the size of each habitat patch decreases.
C) patches become more isolated from each other.
D) patches become less isolated from each other.
E) colonization rates decline because dispersal is limited.

Question 68

Based on the principles of island biogeography,one practical step restoration ecologists could take to limit the negative effects of fragmentation is to leave dispersal corridors.A second step is to

A) decrease colonization.
B) decrease average patch size.
C) remove nonessential species from patches.
D) keep average patch size as large as possible.
E) keep patches as far from each other as possible.

Question 69

Two 1-km² areas of mature forest are at the same latitude.Area A is surrounded by developed land with housing and shopping centers.Area B is in the center of a 100-km² conservation area of mature forest.A team of scientists does surveys to determine the diversity of arthropod species in both areas.Which area will likely show greater species diversity,and why?

A) Area A,because it will have lower levels of vertebrate predation
B) Area A,because its smaller favorable habitat will cause greater aggregation of arthropod populations
C) Area B,because its herbivorous arthropods have decreased competition for food
D) Area B,because it is less isolated from a species pool of potential arthropod immigrants
E) Areas A and B will show approximately equal diversities because they have the same areas,habitats,and latitudes and will attract equal numbers of species.

Question 70

Introduction of new dung beetle species into Australia eventually resulted in a species composition that enabled decomposition of built-up dung,improved soil quality and net primary productivity,and made cattle healthier.This series of events illustrates the value of

A) extinctions.
B) ecosystem services.
C) ecological succession.
D) ecological transitions.
E) the theory of island biogeography.

Question 71

In Brazil,corridors have been left to connect some fragmented forest patches to undisturbed forest.This form of forest management is beneficial because it

A) provides a method of species dispersal to and from the fragments.
B) eliminates the process of colonization in the fragments.
C) enables the deforested areas to be repopulated and to regrow.
D) forces species in the fragments out into the undisturbed forest.
E) eliminates the process of extinction in the fragments.

Question 72

The introduction of a large predatory fish species into a lake will lead to declines in populations of smaller fish,which in turn cause an increase in plankton.This series of events is one example of

A) succession.
B) species turnover.
C) a trophic cascade.
D) a keystone exchange.
E) an ecological transition.

Question 73

The value of ecosystem services depends greatly on an ecological factor that humans can maintain with careful management.This factor is

A) species diversity.
B) population density.
C) climatic conditions.
D) trophic interactions.
E) species composition.

Question 74

Between 1950 and 1985,half of Central America's tropical forests were cut,and the remainder was scattered in small isolated fragments.Another 19 percent of the forest had disappeared by 2005.A survey of the remaining tropical forest areas would most likely show

A) increased species richness.
B) decreased species richness.
C) decreased extinction rates.
D) increased colonization rates.
E) increased primary productivity.

Question 75

The theory of island biogeography can be applied to oceanic islands as well as to other types of habitat islands.For which of these habitats,however,would it be least relevant?

A) A coral reef split in half by dredging
B) A national park surrounded by cities and suburbs
C) A coastal area being recolonized after a hurricane
D) A large nature preserve surrounded by farmland
E) A tropical forest fragmented by deforestation to make farms

Question 76

The theory of island biogeography can best be applied to ecosystems damaged by

A) erosion.
B) pollution.
C) a sudden disturbance.
D) habitat fragmentation.
E) loss of net primary productivity.

Question 77

An island begins to recolonize after a volcanic eruption.In the first year of recolonization,20 new species become established.In the second year,10 new species become established,and in the third year,5 species become established.The decrease in number of colonizing species over time most likely occurs because by years 2 and 3

A) more arrivals represent already established species.
B) fewer species from the mainland are available to colonize.
C) fewer species remain that are adapted to island conditions.
D) competition and predation are preventing new species from colonizing.
E) population growth has overwhelmed the island,leaving no space for new species.

Question 78

A small wooded area,once surrounded by pastures and shrubby areas,gradually became enclosed by housing developments.Ecologists studying the area noticed that,as housing developments encroached,some species disappeared from the woodland,but no new species entered.What is the most likely reason for this?

A) The housing developments were damaging the woodland by causing erosion.
B) The housing developments were damaging the woodland by causing air and water pollution.
C) The housing developments acted as a barrier to dispersal into and out of the woodland.
D) Extinction rates increased in the small area,while dispersal rates were unchanged.
E) Colonization rates increased in the small area,while extinction rates remained stable.

Question 79

Accumulated cattle dung in Australian pastures after the introduction of cattle caused pasture productivity to decline because

A) nitrogen was not being recycled.
B) it made the pastures too dry.
C) it made the pastures too wet.
D) too much free nitrogen was present.
E) cattle refused to eat the grass,preventing more from growing.

Question 80

Conservation of critical parts of food webs is important because removal of these critical species may

A) promote succession.
B) trigger trophic cascades.
C) increase ecological efficiency.
D) promote ecological transitions.
E) prevent large-scale disturbances.