15.9–15.15: Species interactions influence the structure of communities.

Interacting species in a community coevolve in a variety of ways, some antagonistic and others mutually beneficial.

Question 15.28

Nitrogen enters the food chain:

  • a) primarily through soil-dwelling bacteria that “fix” nitrogen by attaching it to other atoms.
  • b) from the atmosphere when “fixed” by the photosynthetic machinery of plants.
  • c) when rocks dissolved by rainwater become soil, which is then utilized for plant growth.
  • d) through soil erosion followed by runoff into streams and ponds.
  • e) through methane, produced by herbivores as a by-product of the breakdown of plant material.

Question 15.29

Which of the following statements about an organism’s niche is incorrect?

  • a) It encompasses the space the organism requires.
  • b) It includes the type and amount of food the organism consumes.
  • c) It is not always fully exploited.
  • d) It may be occupied by two species, as long as they are not competitors.
  • e) It reflects the ways in which the organism utilizes the resources of its environment.

Question 15.30

The “ghost of competition past” refers to the fact that:

  • a) competition often leads to character displacement, which remains even after direct competition is reduced.
  • b) competition cannot be seen in nature.
  • c) competition inevitably leads to extinction of one of the competitors.
  • d) competition inevitably leads to extinction of both competitors.
  • e) the fossil record is a record of competitive interactions.

Question 15.31

Chemical defenses are more common among plants than animals because:

  • a) plants cannot move to escape predators and so must develop other deterrents.
  • b) the cell wall can contain the chemicals more effectively than a simple plasma membrane.
  • c) mechanical defenses against predators can evolve only in animals.
  • d) parasite loads are significantly higher in plants than in animals.
  • e) All of the above are correct.

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