1. Community Ecology

2. Two-species interactions are classified by the impact each species has on the other. Thus, a competitive interaction is one where the populations of each species are hurt by the presence of the other species, usually because each species uses the same resources. Niche partitioning enables species to coexist by
avoiding direct competition.
encouraging mutualistic interactions.
enabling prey to hide from predators.
creating new resources.
allowing abiotic factors, such as climate or nutrient availability, to influence the community.
Answer: a

3. Two-species interactions are classified by the impact each species has on the other. Thus, a competitive interaction is one where the populations of each species are hurt by the presence of the other species, usually because each species uses the same resources. Niche partitioning enables species to coexist by
avoiding direct competition.
encouraging mutualistic interactions.
enabling prey to hide from predators.
creating new resources.
allowing abiotic factors, such as climate or nutrient availability, to influence the community.

4. Which of the following best describes resource partitioning?
Two species can coevolve to share identical niches.
Competitive exclusion results in the success of the superior species.
A climax community is reached when no new niches are available.
Slight variations in niche allow similar species to coexist.
Differential resource utilization results in the decrease in community species diversity.
Answer: d 4

5. Which of the following best describes resource partitioning?
Two species can coevolve to share identical niches.
Competitive exclusion results in the success of the superior species.
A climax community is reached when no new niches are available.
Slight variations in niche allow similar species to coexist.
Differential resource utilization results in the decrease in community species diversity. 5

6. What is one difference between the fundamental niche and the realized niche?
The realized niche is larger.
The fundamental niche is determined by competitors
The realized niche is determined by abiotic resources.
Individuals will be found only in the realized niche.
The difference is called the occupied niche.
Answer: d 6

7. What is one difference between the fundamental niche and the realized niche?
The realized niche is larger.
The fundamental niche is determined by competitors
The realized niche is determined by abiotic resources.
Individuals will be found only in the realized niche.
The difference is called the occupied niche. 7

8. character displacement. temporal niche partitioning.
The common spiny mouse (Acomys cahirinus) and the golden spiny mouse (A. russatus) can occupy essentially the same ecological niche. They accomplish this by
character displacement.
temporal niche partitioning.
eating different foods.
mating at different times of the year.
each occupying their functional niche.
Answer: b 8

9. character displacement. temporal niche partitioning.
The common spiny mouse (Acomys cahirinus) and the golden spiny mouse (A. russatus) can occupy essentially the same ecological niche. They accomplish this by
character displacement.
temporal niche partitioning.
eating different foods.
mating at different times of the year.
each occupying their functional niche. 9

10. An obligate mutualism is an interaction in which at least one species cannot survive without the presence of the other species; a facultative mutualism is an interaction that benefits both species but is not required by either species. One reason facultative mutualism is more common is that
in an obligate mutualism, if the partner becomes extinct, the obligate mutualist will also become extinct.
in a facultative mutualism, if the partner becomes extinct, the obligate mutualist will also become extinct.
in an obligate mutualism, the obligate mutualist is obliged to support its partner.
in a facultative mutualism, neither partner can depend on the other partner.
facultative mutualisms require longer periods of time to evolve.
Answer: a 10

11. An obligate mutualism is an interaction in which at least one species cannot survive without the presence of the other species; a facultative mutualism is an interaction that benefits both species but is not required by either species. One reason facultative mutualism is more common is that
in an obligate mutualism, if the partner becomes extinct, the obligate mutualist will also become extinct.
in a facultative mutualism, if the partner becomes extinct, the obligate mutualist will also become extinct.
in an obligate mutualism, the obligate mutualist is obliged to support its partner.
in a facultative mutualism, neither partner can depend on the other partner.
facultative mutualisms require longer periods of time to evolve. 11

12. This graph shows the effect of soil pH on microbial diversity
This graph shows the effect of soil pH on microbial diversity. One conclusion you should draw from this figure is
the higher the soil pH, the higher the microbial diversity.
the lower the soil pH, the higher the microbial diversity.
microbes eat pH.
the scientists couldn’t find any acidic or basic soils.
there appears to be an optimal pH value for maximizing microbial diversity.
Answer: e 12

13. This graph shows the effect of soil pH on microbial diversity
This graph shows the effect of soil pH on microbial diversity. One conclusion you should draw from this figure is
the higher the soil pH, the higher the microbial diversity.
the lower the soil pH, the higher the microbial diversity.
microbes eat pH.
the scientists couldn’t find any acidic or basic soils.
there appears to be an optimal pH value for maximizing microbial diversity. 13

14. Look at the following figure, which shows a partial Chesapeake Bay food web. If sea nettles disappeared,
there would be fewer fish eggs.
there would be more striped bass.
there would be fewer zooplankton.
striped bass would have less food to eat.
sea nettles would reinvade from the ocean.
Answer: b 14

15. Look at the following figure, which shows a partial Chesapeake Bay food web. If sea nettles disappeared,
there would be fewer fish eggs.
there would be more striped bass.
there would be fewer zooplankton.
striped bass would have less food to eat.
sea nettles would reinvade from the ocean. 15

16. In rocky intertidal communities of western North America, Robert Paine removed Pisaster, an uncommon starfish, and measured species diversity. He found species diversity dropped dramatically when Pisaster was not present. From this, we can conclude that
uncommon species are more vital to the community than common species.
predators are more vital to the community than prey.
Pisaster likely consumed the dominant competitors.
Robert Paine’s experiment was poorly designed.
removing one species always hurts the community.
Answer: c 16

17. In rocky intertidal communities of western North America, Robert Paine removed Pisaster, an uncommon starfish, and measured species diversity. He found species diversity dropped dramatically when Pisaster was not present. From this, we can conclude that
uncommon species are more vital to the community than common species.
predators are more vital to the community than prey.
Pisaster likely consumed the dominant competitors.
Robert Paine’s experiment was poorly designed.
removing one species always hurts the community. 17

18. Disturbance is an important component of succession because it
a) removes keystone species.
b) changes the biome from one kind to another.
c) introduces invasive species.
d) is associated with humans.
e) tends to promote earlier successional stages.
Answer: e 18

19. Disturbance is an important component of succession because it
a) removes keystone species.
b) changes the biome from one kind to another.
c) introduces invasive species.
d) is associated with humans.
e) tends to promote earlier successional stages. 19

20. Which of the following explains mutualism?
− / −
+ / −
+ / +
Answer: c
Mutualism is a relationship where both organisms benefit from the relationship. 20

21. Which of the following explains mutualism?
− / −
+ / −
+ / + 21

22. Scientific Skills Exercises
In the first part of an experiment, researchers collected 12 black snakes (Pseudechis porphyriacus) from areas where cane toads had existed for 40–60 years and another 12 from areas free of cane toads. They offered the snakes either a freshly killed native frog (Limnodynastes peronii, a species the snakes commonly eat) or a freshly killed cane toad from which the toxin gland had been removed (making the toad nonpoisonous).

23. The data are shown below, and a bar graph of the data is shown on the next slide.

25. What do the data suggest about the effects of cane toads on the predatory behavior of black snakes in areas where the toads have been present for 40–60 years?
a) Black snakes will not prey on cane toads in areas where cane toads have been present for 40–60 years.
b) Black snakes will prey on cane toads in areas where cane toads have been present for 40–60 years, but not when offered a native frog instead.
c) Black snakes in areas where cane toads have been present for 40–60 years are just as likely to prey on cane toads as on native frogs.
Answer: a

26. What do the data suggest about the effects of cane toads on the predatory behavior of black snakes in areas where the toads have been present for 40–60 years?
a) Black snakes will not prey on cane toads in areas where cane toads have been present for 40–60 years.
b) Black snakes will prey on cane toads in areas where cane toads have been present for 40–60 years, but not when offered a native frog instead.
c) Black snakes in areas where cane toads have been present for 40–60 years are just as likely to prey on cane toads as on native frogs.

27. What do the data suggest about the predatory behavior of black snakes in areas where cane toads are not currently found
a) In those areas, black snakes will not prey on cane toads.
b) In those areas, black snakes are equally likely to prey on native frogs and cane toads.
c) In those areas, black snakes will prey on cane toads, but they are more likely to prey on native frogs.
Answer: c

28. What do the data suggest about the predatory behavior of black snakes in areas where cane toads are not currently found
a) In those areas, black snakes will not prey on cane toads.
b) In those areas, black snakes are equally likely to prey on native frogs and cane toads.
c) In those areas, black snakes will prey on cane toads, but they are more likely to prey on native frogs.

29. Suppose an enzyme that deactivates the cane toad toxin evolves in black snakes living in areas with cane toads. If the researchers repeated this experiment, predict how the results would change for areas where cane toads have been present for 40–60 years.
a) A much higher percentage of black snakes in those areas would eat the cane toads offered to them.
b) The results would not change significantly.
c) A much lower percentage of black snakes in those areas would eat the cane toads offered to them.
d) A much higher percentage of black snakes in those areas would eat the cane toads offered to them, and a lower percentage would eat the native frogs offered to them.
Answer: a

30. Suppose an enzyme that deactivates the cane toad toxin evolves in black snakes living in areas with cane toads. If the researchers repeated this experiment, predict how the results would change for areas where cane toads have been present for 40–60 years.
a) A much higher percentage of black snakes in those areas would eat the cane toads offered to them.
b) The results would not change significantly.
c) A much lower percentage of black snakes in those areas would eat the cane toads offered to them.
d) A much higher percentage of black snakes in those areas would eat the cane toads offered to them, and a lower percentage would eat the native frogs offered to them.

31. Based on the scatter plot, what conclusion would you draw about whether exposure to cane toads is having a selective effect on black snakes in this study?
a) Exposure to cane toads does not appear to have a selective effect on black snake populations.
b) Exposure to cane toads appears to be selecting for black snakes that are less affected by the toxin.
c) Exposure to cane toads appears to be selecting for black snakes that are more affected by the toxin.
d) Exposure to cane toads appears to be selecting for black snakes that are faster swimmers.
Answer: b

32. Based on the scatter plot, what conclusion would you draw about whether exposure to cane toads is having a selective effect on black snakes in this study?
a) Exposure to cane toads does not appear to have a selective effect on black snake populations.
b) Exposure to cane toads appears to be selecting for black snakes that are less affected by the toxin.
c) Exposure to cane toads appears to be selecting for black snakes that are more affected by the toxin.
d) Exposure to cane toads appears to be selecting for black snakes that are faster swimmers.