Question

cacti with very few spines tend to be eaten by animals, and cacti with many spines tend to be preferred by parasitic insects. this causes cacti with an average number of spines to be preferred. how would you explain this?
a) this is an example of a stabilizing selection in which the intermediate form of a trait is advantageous compared to the extreme forms of the trait.

b) this is an example of directional selection in which one end of the bell curve is better adapted to its environment than the other end.

c) this is an example of bidirectional selection in which evolutionary pressures from multiple sources encourage an organism to adapt.

d) this is an example of a disruptive selection in which the population of cacti is divided and well defined.

question 6 (5 points)

Explanation:

• Option A: Stabilizing selection favors intermediate traits (average spine number here) as extreme traits (very few or many spines) are disadvantaged (eaten by animals or preferred by parasites). The graph shows the starting population's bell - curve narrowing around the average, matching stabilizing selection.
• Option B: Directional selection shifts the population towards one extreme trait, but here the average is favored, not a shift to an extreme.
• Option C: "Bidirectional selection" is not a standard type of natural selection. The standard types are stabilizing, directional, and disruptive.
• Option D: Disruptive selection favors extreme traits and splits the population, but here the average is favored, not the extremes.

Answer:

A) This is an example of a stabilizing selection in which the intermediate form of a trait is advantageous compared to the extreme forms of the trait.