Understanding the factors that control species distributions has long been of in

Question

Understanding the factors that control species distributions has long been of interest to ecologists. On rocky shores, the upper borders of species distributions are generally assumed to be set by physical factors while lower borders are set by biotic interactions such as predation and competition. Researchers studied the survival of barnacles in the intertidal zone as a function of predators (adult crab, juvenile crab, no crab) and barnacle density (WN, with neighbors, or S, solitary (no neighbors)). Consider the following figure:

1) What is/are the independent variable(s)?       

a) predators

b) barnacle density

c) predators and barnacle density

d) barnacle survival

2) What is/are the dependent variable(s)

a) predators

b) density

c) predators and barnacle density

d) barnacle survival

3) How many different treatment combinations are there in this experimental design?

a) two

b) three

c) six

d) twelve

4) Which treatment would you consider to be the “control”?

a) solitary (no neighbors)

b) no crab

c) solitary, no crab

d) no barnacle     

5) Which treatment appears to have had the greatest impact on barnacle survival?

a) solitary, no crab

b) solitary, adult crab

c) with neighbors, adult crab

d) cannot be determined

6) Not considering competition, what effect did predators have on barnacle survival?    

a) positive

b) negative

c) none

d) depends on the predator

7) Not considering predation, what effect did competitors have on barnacle survival?

a) positive

b) negative

c) none

d) depends on the competitor

8) Based on these results, what factor(s) control barnacle distributions in the rocky intertidal zone?

a) predation

b) competition

c) predation and competition

d) temperature

Explanation / Answer

2. barnacle survival

6. depends on the predator

7. negative

8. predation

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