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Question 5 of 5

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SAT Subject Test

Known numbers of seeds from two species (X and Y) of annual plants are mixed together in different proportions and planted in five small plots of soil in the spring. The plants grow, flower, and produce seeds. It is found that the percentage of seeds of species X and species Y in the harvest is usually different from the proportion that was planted, although the total number of seeds produced is the same as the number of seeds planted. The data are plotted on the graph below.

GRAPH

What do the data indicate about the ecological relationship between species X and species Y?

Select an Answer

X and Y are mutualistic for low percentages of X seeds.

Correct Answer: 
No

X and Y are mutualistic for high percentages of X seeds.

Correct Answer: 
No

X and Y compete when both X and Y seeds are present.

Correct Answer: 
Yes

Y competes successfully against X at all percentages of X and Y seeds.

Correct Answer: 
No

X is a parasite of Y when Y is rare.

Correct Answer: 
No

The graph shows that the survival of either of the two species depends on the relative abundance of each species at the time of seed planting. In a mutualistic relationship both species benefit, but the data do not show that this is true at either low or high percentages of species X, ruling out choices (A) and (B). Species Y does not compete successfully against species X in all mixtures, ruling out choice (D). There is no evidence for parasitism, ruling out choice (E). Competition occurs in all seed mixtures and species X is a stronger competitor in most of the seed mixtures.

Question Difficulty: 
hard