Deck 17: Change in Communities

Question 1

Refer to the figure.
On Mount St. Helens, the intensity of disturbance ranged from extremely high (lava dome, pumice plain) to moderate (mudflow zone, blowdown zone), to low (scorch zone).

-In which area is the abiotic stress of low nitrogen availability most likely to control succession?

A) Pumice Plain
B) Mudflow zone
C) Blowdown zone
D) Scorch zone

Answer 1

Pumice Plain

Question 2

Refer to the figure.
On Mount St. Helens, the intensity of disturbance ranged from extremely high (lava dome, pumice plain) to moderate (mudflow zone, blowdown zone), to low (scorch zone).

-In which area is the biotic stress of competition most likely to control succession?

A) Pumice Plain
B) Mudflow zone
C) Blowdown zone
D) Scorch zone

Answer 2

Scorch zone

Question 3

Which statement about change in communities is true?

A) Only biotic factors can be agents of change.
B) Only abiotic factors can be agents of change.
C) Disturbances create opportunities for some species to grow or reproduce due to the injury or death of other individuals.
D) "Stress" and "disturbance" are interchangeable words that describe the same processes.

Answer 3

C

Question 4

Which of the following is not an abiotic factor that can be an agent of change?

A) A hurricane
B) Acid rain
C) An ice storm
D) Digging

Question 5

Which of the following is a biotic factor that can be an agent of change?

A) Competition
B) Drought
C) A hurricane
D) A forest fire

Question 6

Which of the following would be considered a community stress?

A) A beaver population that is causing trees to fall
B) Acidity in the water that is limiting the reproduction of certain fish species
C) A fire that destroys half of the trees in an area
D) Predation by a new predator

Question 7

Refer to the figure.
The figure shows examples of possible disturbance intensity (y-axis) and frequency (x-axis) combinations.

- What type of disturbance would be likely represented by B?

A) Flood
B) Active volcano
C) Hurricane
D) Forest fire

Question 8

Refer to the figure.
The figure shows examples of possible disturbance intensity (y-axis) and frequency (x-axis) combinations.

-What type of succession occurs after the disturbance in A?

A) Primary succession
B) Secondary succession
C) Climax
D) Little succession occurs

Question 9

Refer to the figure.
The figure shows examples of possible disturbance intensity (y-axis) and frequency (x-axis) combinations.

- What type of succession occurs after the disturbance in C?

A) Primary succession
B) Secondary succession
C) Climax
D) Little succession occurs

Question 10

Refer to the figure.
The figure shows examples of possible disturbance intensity (y-axis) and frequency (x- axis) combinations.

- What type of succession occurs after the disturbance in D?

A) Primary succession
B) Secondary succession
C) Climax
D) Little succession occurs

Question 11

Which type of succession involves colonization of habitats devoid of life?

A) Primary
B) Secondary
C) Pristine
D) Abiotic

Question 12

Which statement about early primary succession is false?

A) The process can be very slow.
B) The first colonists typically cannot withstand much physiological stress.
C) The first colonizers usually can modify the habitat to benefit their growth and reproduction.
D) The first colonists typically face hostile conditions.

Question 13

The final theoretical stage of succession is called the _______ stage.

A) omega
B) ultimate
C) penultimate
D) climax

Question 14

Assume that the melting of a glacier is taking place at a constant rate of 50 meters per year, and that site A is 1.6 km farther from the ice edge than site B is. Based on this data, and the principle of "space for time substitution," we can assume that the conditions seen at site A in the year 2011 are the same as those that _______ seen at site B in _______.

A) were; 1979
B) were; 1995
C) will be; 2027
D) will be; 2043

Question 15

If Cowles is correct about succession, then

A) space can be substituted for time.
B) the unique conditions in particular locations are of great importance.
C) we do not have the ability to make inferences about the changes in communities over time scales that span centuries.
D) succession is usually unpredictable.

Question 16

In the dunes near Lake Michigan studied by Cowles, the dominant plant species in the early stages of succession was

A) spike grass.
B) American beach grass.
C) Indiana dune grass.
D) Michigan cord grass.

Question 17

Which early ecologist maintained that plant communities are analogous to "superorganisms"?

A) Henry Cowles
B) Fredrick Clements
C) Henry Gleason
D) F. Stuart Chapin

Question 18

Which statement best summarizes Elton's views on succession?

A) Plant communities are like "superorganisms"-that is, groups of species that work together in a mutual effort toward some deterministic end.
B) Each community has its own predictable life history; left undisturbed, the community will ultimately reach a stable, predetermined endpoint.
C) Organisms and the environment interact to shape the direction that succession will take.
D) Communities are like an organism with various interacting parts; responses to the prevailing conditions by individual species matter little.

Question 19

Suppose that following a lava flow, pine grass (a hypothetical species) is the first species to colonize the area. Chemicals produced by pine grass change the soil chemistry in the environment, but these chemicals promote subsequent colonization by later species. Which model would best explain this scenario of succession?

A) Inhibition
B) Tolerance
C) Facilitation
D) Compensation

Question 20

The tolerance and the inhibition models of primary succession hold different assumptions about the

A) nature of the effects that the early colonizing species have on other early colonizing species.
B) nature of the disturbances and the opportunities they provide.
C) nature of the effects that the early colonizers have on late colonizing species.
D) strength of the disturbances and the extent of their impact on the habitat.

Question 21

According to the _______ model of succession, the early successional species modify the environment so as to facilitate the subsequent colonization of other early colonizing species.

A) facilitation
B) tolerance
C) inhibition
D) None of the above

Question 22

Refer to the figure.
In their work on aspen-fir interactions, Calder and St. Clair claim that aspens are facilitated by the presence of fir trees. From these data, what is the primary evidence for aspen being facilitated by fir?

A) Aspen mortality increases when they are within 0.5 m of a fir tree.
B) Fir mortality is highest when at distances greater than 0.5 m from aspen.
C) Aspen mortality decreases when they are within 0.5 m of a fir tree.
D) Aspen mortality is highest in fir-dominated stands.

Question 23

Suppose that a late succession plant that is surrounded by early succession plants grows at a rate of 0.5 cm per day. If the early succession plants are removed experimentally, the late succession plants are observed to grow at a rate of 0.9 cm per day. This experiment shows that the early succession plants have a _______ effect on the late succession plants, and this observation is most consistent with the _______ model of succession.

A) positive; facilitation
B) positive; inhibition
C) negative; facilitation
D) negative; inhibition

Question 24

In his studies of succession in Glacier Bay, Chapin found that as communities went from early to latter stages of succession, soil moisture _______ and nitrogen _______.

A) increased; increased
B) increased; decreased
C) stayed about the same; increased
D) decreased; increased

Question 25

In their studies of succession in Glacier Bay, Alaska, Chapin and colleagues found that the survival rate of germinated spruce seeds was highest at the _______ stage.

A) pioneer
B) Dryas
C) alder
D) spruce

Question 26

The studies by Chapin and colleagues on Glacier Bay succession provide empirical support for which model(s) of succession?

A) Facilitation only
B) Tolerance only
C) Inhibition only
D) Facilitation, tolerance, and inhibition

Question 27

Refer to the figure.
Chapin et al. conducted their work in Glacier Bay in 1994. If we were to return today to his plots, what could we predict to find in his former ten year-old pioneer communities that had been dominated by low shrubs, herbs, mosses, liverworts, and lichens?

A) Largely the same community, but slightly more diverse
B) Many of the same species, but with some tall shrubs
C) A community dominated by the small shrub Dryas drummondii
D) A community where Sitka spruce (Picea sitchensis) and alders (Alnus sinuata) co-dominate with diverse subcanopy species

Question 28

At which stage of succession is facilitation usually the most significant factor?

A) Early
B) Middle
C) Late
D) Facilitation is equally important in middle and late stages.

Question 29

Refer to the figure.
In Farrell's (1991) work on algal succession, the presence of limpets had what effect on the growth of algae?

A) Limpets facilitate algal succession.
B) Limpets tolerate algal succession.
C) Limpets inhibit algal succession.
D) The role of limpets depends on the presence or absence of Balanus.

Question 30

Which statement about succession in the glaciers of Alaska is false?

A) The observations of Cooper were consistent with Cowles's theory of "space for time substitution."
B) The earliest stage is dominated by alders.
C) The stage dominated by spruce is more mature than the one dominated by alders.
D) There is a general increase in species diversity from the Dryas stage to the alder stage.

Question 31

You are in Glacier Bay. Starting at a location dominated by alders, you would most likely first run into the _______ stage if you travelled toward the glacier's edge and the _______ stage if you travelled away from the glacier's edge.

A) pioneer; Dryas
B) pioneer; spruce
C) Dryas; spruce
D) spruce; Dryas

Question 32

Which manipulation(s) did Bertness and Shumway perform in their studies of succession in a New England salt marsh?

A) Adding spruce seeds at various stages of succession
B) Watering certain plots with salt water to alleviate salt stress
C) Selectively removing particular plant species from newly colonized plots
D) Protecting some plots from damage from waves

Question 33

In their manipulative studies of succession in a New England salt marsh, Bertness and Shumway altered salt stress in certain fields by

A) adding salt.
B) introducing microbes that filter out salt.
C) shading the soil's surface.
D) watering the fields with fresh water.

Question 34

Bertness and Shumway's studies of high salt stress conditions in the middle intertidal regions of New England salt marshes led to which conclusion?

A) Juncus drove Distchlis to extinction.
B) Spartina inhibited colonization by Juncus.
C) Distichlis facilitated colonization by Juncus.
D) Distichlis inhibited colonization by Juncus.

Question 35

Sousa's studies of intertidal zones in southern California showed that

A) succession was driven primarily by facilitation.
B) the first species to colonize was the same across patches.
C) the first species to colonize varied across patches.
D) succession was driven primarily by inhibition.

Question 36

Farrell's studies of algal succession on the Oregon coast showed that

A) algal succession is driven primarily by inhibition.
B) Balanus facilitated the growth of algae by protecting them from limpet herbivory.
C) Balanus facilitated the growth of algae by secretion of nitrogenous compounds.
D) Limpets facilitated the growth of algae by providing surfaces on which they could rest.

Question 37

Refer to the figure.
The figure is derived from studies of algal succession in the presence and absence of the barnacle Balanus and limpets. Which condition is represented by the purple line (indicated by the black arrow)?

A) The presence of both limpets and Balanus
B) The presence of limpets and the absence of Balanus
C) The presence of Balanus and the absence of limpets
D) The absence of both limpets and Balanus

Question 38

Alternative stable states most often arise

A) in terrestrial ecosystems.
B) in intertidal zones.
C) when there are strong interactions among species.
D) under the tolerance model of succession.

Question 39

Which principle is best supported by the results of Sutherland's studies in which fish predators were excluded from a marine fouling community?

A) Communities can follow different successional paths and display alternative states.
B) Predation is a relatively unimportant factor in succession in marine communities.
C) In most marine systems, the tolerance model accurately predicts successional outcomes.
D) Facilitation is most important in early succession, whereas inhibition becomes more important in later stages.

Question 40

Connell and Sousa criticized Sutherland's experiments on alternative stable states in fouling communities on the grounds that

A) the experiments were conducted over too much time.
B) fouling communities without predators may not be sustainable in nature.
C) the system clearly demonstrated hysteresis.
D) the predator-exclusion cages were not totally effective.

Question 41

Refer to the figure.
Suppose you are studying succession patterns in two species, species A and species B, both small aquatic organisms that colonize bare surfaces underwater. You replicated Sutherland's experiments in this new system by placing bare tiles underwater in predator-protected areas and areas with predators. You collect data on the percent of cover for each species, as shown in the figure.

- Without predation, which species is a better competitor?

A) Species A is a much better competitor than species B.
B) Species A is a slightly better competitor than species B, but there is a lot of variability.
C) Species B is a much better competitor than species A.
D) Species B is a slightly better competitor than species A, but there is a lot of variability.

Question 42

Refer to the figure.
Suppose you are studying succession patterns in two species, species A and species B, both small aquatic organisms that colonize bare surfaces underwater. You replicated Sutherland's experiments in this new system by placing bare tiles underwater in predator-protected areas and areas with predators. You collect data on the percent of cover for each species, as shown in the figure.

- Based on the data, what would you expect that a newly colonized area in a natural pond would look like?

A) Species A would dominate species B, although species B would still occupy some space.
B) Species A and B would coexist at about equal proportions.
C) Species B would dominate species A, although species A would still occupy some space.
D) The predators in the natural ponds would cause both species A and species B populations to decrease significantly.

Question 43

Which human activity can bring about shifts in communities to alternative stable states?

A) Habitat destruction
B) Introduction of invasive species
C) Overexploitation of native species
D) All of the above

Question 44

Which statement about the amphibians that colonized the area around Mount St. Helens after the eruption is true?

A) The frog Rana cascadae was the most important animal ecosystem engineer in the community.
B) Frogs and salamanders started to colonize the area within the first few years of the eruption.
C) By the year 2000, the species diversity of amphibians had reached pre-eruption levels.
D) Both a and b

Question 45

In the succession that followed the eruption of Mount St. Helens, which organism played an important role as an ecosystem engineer?

A) The toad Bufo boreas
B) The frog Rana cascadae
C) The pocket gopher Thomomys talpoides
D) The salamander Ambystoma gracile

Question 46

Plants with bacterial symbionts that fix _______ are often important players in _______ stages of succession.

A) nitrogen; early
B) phosphorus; late
C) sulfur; early
D) phosphorus; early

Question 47

Which statement about plants with nitrogen-fixing bacteria is true?

A) They often play major roles in early succession.
B) They are often at a competitive disadvantage in late succession due to the energetic costs involved in maintaining their bacterial symbionts.
C) Only a few types of nitrogen-fixing bacteria are associated with plants.
D) Both a and b

Question 48

Refer to the figure.
Figure 1
You are studying succession in an area affected by a volcanic eruption. Figure 1 shows the amount of volcanic activity over time, from no activity to high activity. Time periods with no activity indicate that the volcano is inactive and no disturbance is occurring; time periods with high activity indicate that the volcano is active and there are high levels of disturbance.Answer the following questions:
a) How would you describe the frequency of eruptions in terms of ecological timescales? Are eruptions common or rare in this area compared to the lifespan of organisms?
b) Using the frequency of eruptions, create a graph (this will be referred to as Figure 2) that shows where this type of event would be located on the plot of the spectrum of disturbance. Make the x-axis frequency (from low to high), and the y-axis intensity (from low to high).
c) Based on the frequency and intensity of the eruptions, what type of successional response would you predict for this area?

Question 49

Refer to the figures.
Figure 1
Figure 3
You are studying two islands (Figure 3) that have recently experienced volcanic activity. Both were formerly forested with palm trees. On island 1, a heat wave resulting from the volcanic eruption leads to the destruction of all the above-ground vegetation (middle figure). On island 2, a lava flow resulting from the volcanic eruption (right figure) completely covers the island.Answer the following questions:
a) How have the resources, environmental conditions, and species communities likely changed on the two islands as a result of the volcanic eruption?
b) Assume that the frequency of eruptions on the islands follows the pattern shown in Figure 1. Using data from Figures 1 and 3, create a graph (this will be referred to as Figure 4) using the frequency of eruptions to show where island 1 and island 2 would be located on the spectrum of disturbance. The x-axis should be frequency and the y-axis should be intensity.
c) Based on the frequency and intensity of the eruptions you plotted in Figure 4, what type of successional response would you predict for each island?

Question 50

Refer to the figures.
Figure 5
Figure 6
Figure 7
You are studying the impacts of a volcanic eruption that produces a lava flow that covers part of a grassland (Figure 5). You begin taking samples as soon as the area is safe to work in-about one year after the main eruption has ended. You set up a transect (beginning at "Transect start" in Figure 5), and then collect data on how several abiotic and biotic factors vary across it (Figures 6 and 7).

-Answer the following questions:
a) According to the data in Figure 6, what was the effect of the eruption on the percent of organic material in the soil along the transect?
b) Based on Figure 5, predict how the eruption would have changed the amount of UV reaching ground level along the transect. Graph your prediction (this will be referred to as Figure 8).
c) Based on the available resources, what type of succession would you expect along the transect? In both the blast zone and lava flow areas, how extreme are the conditions faced by the colonizer species? How would you expect the extent of extreme conditions to limit the species that could potentially colonize the areas?

Question 51

Refer to the figures.
Figure 5
Figure 6
Figure 7
You are studying the impacts of a volcanic eruption that produces a lava flow that covers part of a grassland (Figure 5). You begin taking samples as soon as the area is safe to work in-about one year after the main eruption has ended. You set up a transect (beginning at "Transect start" in Figure 5), and then collect data on how several abiotic and biotic factors vary across it (Figures 6 and 7).

-As part of your long-term research, you look into the succession patterns along the transect. Would a space for time substitution allow you to predict succession patterns in the lava flow area based on succession you observe in the blast zone? Why or why not? How is this situation similar or different from other situations that use space for time substitutions?

Question 52

Refer to the figure.
Figure 9
You are studying disturbance and succession patterns, focusing on data you collect in area 1, area 2, and area 3. Part A of the figure shows how the community type changed across each year sampled, and part B shows how the abiotic conditions changed across study years (no specific condition specified or units listed).

-Answer the following questions:
a) According to the data in in Figure 9, when did the disturbance occur?
b) Which years would provide baseline data for these communities? Why is baseline data important?
c) How many years did it take the abiotic conditions to return to levels similar to their original conditions?
d) How many years did it take for the biotic communities in areas 1, 2, and 3 to return to their original conditions?

Question 53

Refer to the figure.
Figure 9
You are studying disturbance and succession patterns, focusing on data you collect in area 1, area 2, and area 3. Part A of the figure shows how the community type changed across each year sampled, and part B shows how the abiotic conditions changed across study years (no specific condition specified or units listed).

- According to the data in Figure 9, which area had the most stable community type in comparison to the changes in the abiotic conditions? Justify your answer.

Question 54

Refer to the figure.
Figure 9
You are studying disturbance and succession patterns, focusing on data you collect in area 1, area 2, and area 3. Part A of the figure shows how the community type changed across each year sampled, and part B shows how the abiotic conditions changed across study years (no specific condition specified or units listed).

- Evaluate the successional paths for all three areas to answer the following questions:
a) What is hysteresis?
b) Which area shows evidence for this condition? Explain your answer.

Question 55

Refer to the tables and the figure.
Figure 10
You are studying succession and colonization at two sites, site 1 and site 2. You sample the abundance of two species at the sites and determine their percent cover at each site and time period. Your data are shown in Tables 1 and 2 and are graphed in Figure 10.Answer the following questions:
a) Based on percent cover of species 1 and species 2 at each site, determine the percent of space that is both occupied and unoccupied at each site for each time period. Enter the data into Tables 1 and 2 to create two new tables (these will be referred to as Tables 3 and 4).
b) Using the data in Tables 1 and 2, add lines to the graphs in Figure 10 to plot how the percent of unoccupied space changed over time at both sites (this will be referred to as Figure 11).
c) Using the data in Figure 10, create a table (this will be referred to as Table 5) with summary data on each site. Answer each question for each site.
• How much biomass was present at time 0?
• Which species was the earlier colonist?
• What type of succession occurred early in the study period?
• Which species is dominant at time 8?
• When is the total amount of available area fully utilized by the species at each site?

Question 56

Refer to the figure.
Figure 10
You are studying succession and colonization at two sites, site 1 and site 2. You sample the abundance of two species at the sites and determine their percent cover at each site and time period. Based on the data in Figure 10, does either site show evidence for facilitation? Why or why not?

Question 57

Refer to the figure.
Figure 10
You are studying succession and colonization at two sites, site 1 and site 2. You sample the abundance of two species at the sites and determine their percent cover at each site and time period. Use the data in Figure 10 and your knowledge of the different successional paths that communities can follow to answer the following questions:
a) Are the patterns of changes in abundance of species 1 and 2 consistent across the two sites?
b) Based on the consistency of abundances of species 1 and 2 across the sites, how would you describe the successional patterns observed at sites 1 and 2? What might be driving this pattern?

Question 58

Refer to the tables and the figure.
Figure 11
You are studying succession and colonization at two sites, site 1 and site 2. You sample the abundance of two species at the sites and determine their percent cover at each site and time period.Answer the following questions:
a) When are the sites most vulnerable to colonization by an invasive species? Justify your answer.
b) By time 8, which site is least vulnerable to colonization by an invasive species? Why?

Question 59

A mudslide kills a large fraction of a population of a flower species. The reduction in this flower population allows for an increase in the population size of a fern that competes with the flower. This is an example of

A) stress.
B) primary succession.
C) disturbance.
D) facilitation.

Question 60

What type of disturbance regime is most likely to result in gradual changes in community composition?

A) Intense, infrequent disturbance
B) Intense, frequent disturbance
C) Weak, infrequence disturbance
D) Weak, frequent disturbance

Question 61

A region that is experiencing very frequent disturbances of intermediate intensity will most likely exhibit _______. If the intensity of these disturbances increases noticeably, the region will most likely exhibit _______.

A) primary succession; secondary succession
B) primary succession; extinction of all life
C) secondary succession; primary succession
D) secondary succession; extinction of all life

Question 62

A forest community has reestablished itself after an ice storm damaged most, but not all, of the trees in one area. Which type of succession best describes the reestablishment of the community after the storm?

A) Climax
B) Secondary
C) Primary
D) Biotic

Question 63

Which statement concerning Cowles's early work on succession is false?

A) American beach grass was found to act as an ecosystem engineer by trapping sand that provides refuge for other plants.
B) Cowles assumed the principle of "space for time substitution."
C) American beach grass was found to be the dominant plant species in the first stage of succession.
D) Cowles assumed that plant assemblages most distant from the lake's edge were the youngest.

Question 64

Assume that a glacier is melting at a constant rate of 50 meters per year and that site A is 1.6 km closer to the ice edge than site B is. Based on this data and the principle of "space for time substitution," we can assume that the conditions seen at site A in 2011 are the same as those that _______ seen at site B in _______.

A) were; 1979
B) were; 1995
C) were; 2003
D) will be; 2027

Question 65

In a hypothetical example of succession, the early succession plants produce toxins that hinder both the subsequent colonization of other early succession species and colonization by later succession plants. This scenario fits the _______ model of succession.

A) inhibition
B) tolerance
C) facilitation
D) Both a and b

Question 66

Suppose that you are in Glacier Bay, Alaska, and standing at a location that is dominated by Dryas. If you moved toward the edge of the glacier, you would most likely next encounter _______. If you moved in the opposite direction, away from the edge of the glacier, you would most likely next encounter _______.

A) lichens and mosses; spruce
B) lichens and mosses; alders
C) alders; lichens and mosses
D) alders; spruce

Question 67

Suppose late succession plants that are surrounded by early succession plants grow at a rate of 0.7 cm per day. If the early succession plants are removed experimentally, the late succession plants are observed to grow at a rate of 0.6 cm per day. This experiment shows that the early succession plants have a _______ effect on the late succession plants, and this observation is most consistent with the _______ model of succession.

A) positive; facilitation
B) positive; tolerance
C) positive; inhibition
D) negative; facilitation

Question 68

Which statement about Bertness and Shumway's studies of succession in a New England salt marsh is true?

A) The researchers manipulated the environment by removing seed predators in some of the plots.
B) These studies provide support for the facilitation model as the predominant explanation for succession in salt marshes under a wide range of conditions.
C) These studies provide support for the inhibition model as the predominant explanation for succession in salt marshes under a wide range of conditions.
D) The studies showed that the trajectory of succession in these salt marshes can be altered by changing the salinity of the soil.

Question 69

Sousa's studies of southern California boulders showed that algal succession is driven predominately by

A) facilitation.
B) tolerance.
C) inhibition.
D) inhibition under low salt conditions and facilitation under high salt conditions.

Question 70

Farrell's studies of intertidal communities along the Oregon coast demonstrated that

A) larger species of barnacles could facilitate growth of algal communities by providing them protection from limpets, but smaller barnacles could not.
B) smaller species of barnacles could facilitate growth of algal communities by providing them protection from limpets, but larger barnacles could not.
C) succession of barnacles is driven primarily by the facilitation model.
D) species of barnacles did not impede limpets from grazing on newly settled macroalgal sporelings.

Question 71

Sutherland's experiments showed that the capacity of the tunicate Styela to dominate communities depends primarily on

A) the ambient temperature.
B) the degree of salinity stress.
C) the presence or absence of fish predators.
D) simple random chance.

Question 72

The inability of a system to shift back to the original community state, even after the original conditions have been restored, is called

A) the photic state.
B) hysteresis.
C) an ecological valley.
D) the climax stage.

Question 73

The regime shift from kelp forests to urchin barrens along the west coast of the United States illustrates how human actions have caused communities to shift to alternate states. This particular shift was caused because of a decline in sea otters, most likely due to hunting. Why would the reintroduction or protection of sea otters not return the system to its original state?

A) Hysteresis suggests that some regime shifts are incredibly difficult to reverse.
B) Sea otters are not the only predator on sea urchins.
C) The increase of orcas (a predator of sea otters) will continue to suppress otter populations.
D) Urchin barrens are the climax community for coastal ecosystems.