Communities with a high level of bacterial diversity are found in many habitats including soil and aquatic environments. Recent studies indicate this diversity is crucial to the functioning of these communities. The same studies have also found that phage abundance plays a critical role in the maintenance of the bacterial diversity within these communities. Are phages a density-dependent or a density-independent regulating factor?

Question

A.  density-dependent
B.  density-independent


Clarify question:
What is the key concept addressed by the question?

What type of thinking is required?
 
Gather Content:
What do you already know about density-dependent versus density-independent factors affecting a community? What other information is related to the question? 
 
Choose Answer:
Given what you now know, what information is most likely to produce the correct answer?
 
Reflection on Process:
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
 

Answer 1

A.  density-dependent

Clarify question:
What is the key concept addressed by the question?
This question requires an understanding of environmental pressures and whether the presence of phages is a density-dependent or density-independent factor the help to regulate the bacterial community.

What type of thinking is required?
This is an evaluate question; you need to evaluate the impact of phages on the diversity of the bacterial community.
 
Gather Content:
What do you already know about density-dependent versus density-independent factors affecting a community? What other information is related to the question? 
Phages are viruses which parasitize bacterial cells. In this situation, the parasites keep any one species of bacteria from becoming dominant which maintains diversity within the community. The effect of the phages on any particular species of bacteria can vary with size of the population of the particular bacteria. At a low population size, the virus will spread slowly and have a small effect on the bacteria. If the population of bacteria is particularly high, the virus (phage) can spread quickly through the population and have a huge effect.
 
Choose Answer:
Given what you now know, what information is most likely to produce the correct answer?
Phages are parasites and parasites move between members of a species faster when population numbers are high. This makes them density-dependent regulators. Parasites play an important role in maintaining bacterial community diversity because they prevent any one species of bacteria from becoming dominant.
 
Reflection on Process:
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
To answer this question you had to ignore certain information in the question to focus on the issue of density-dependent versus density-independent control of populations. The fact that phages help to maintain bacterial diversity is important, but the question if the phage infection is density-dependent or density-independent relates more to whether the size of the bacterial population affect phage infections. Larger populations of bacteria allow phage infections to spread faster, making phages a density-dependent factor.