Question

Based on the results above, you study the settlement patterns of the three species. You establish transects on each of your experimental areas (which are evenly distributed among the upper, middle and lower intertidal zones) and remove all barnacles. Each day, you count the number of colonizers of each species in each transect, then remove them. This allows you to measure colonizing ability (not competition). You do this for 30 days. Based on your results in the table below, and your knowledge of the distribution of these barnacles in the wild (see diagram above) which statement is most likely to be true?
Average settlement rate (individuals/day) in three intertidal zones.

Species
ZONE A B C
Upper Intertidal 30 31 0
Middle Intertidal 30 32 15
Lower Intertidal 28 29 31

a. Species C is the superior competitor in all three intertidal zones.
b. Competition between species A and B explains their distributions in the wild.
c. Physical adaptations to the environment drives the distribution of all three species in the wild.
d. Species A is better adapted to the upper intertidal zone than the middle or lower.

Answer 1

Answer:

c. Physical adaptations to the environment drive the distribution of all three species in the wild.

Explanation:

Options A and B refer to competition between species. The experiment was about the colonizing ability of the three species, and not the interaction among them. So these two options are not correct.

Option D states that species A is better adapted to the upper intertidal zone than the middle or lower. But the table shows that species A is equally adapted to colonize upper and middle intertidal zone, and less adapted to colonize lower zones.

The correct option is C. When these competing species coexist, this is because of niche partitioning or niche differentiation. If there is not any differentiation between them, the dominant species displaces the weak species. In the exposed example,  the three species coexist in the middle and lower zones, which means that they probably have different niches and got adapted to living to their environments. This adaptation to different conditions is what leads to their distribution.    

In the exposed example, species A and B can live in the upper intertidal zone, where species C can not live because they can not tolerate environmental conditions. The three species can live in the middle zone, but still, A and B are more adapted to this area than C. Among A and B, B is the most adapted to living in the upper and middle zones. Species C seems to be very adapted to live in the lower intertidal zone, where species A and B can also live, but are less adapted to this area, probably due to environmental conditions or due to their vulnerability to predation. In this last area, species A is less adapted.