Question

Observations of algal species showed that their diversity was higher in pools where there were grazing snails compared to pools without snails. Which one of the following statements best explains this result?

• A. Snails feed preferentially on the more abundant algal species.
• B. Snails avoid feeding on algal species.
• C. Snails feed only on the less abundant algal species.
• D. Snails feed equally on all the algal species irrespective of algal abundance.

Hint:

In ecology, grazers and predators often {increase diversity} by suppressing dominant competitors. Look for options that describe {preferential removal of abundant species}.

Answer 1

The Correct Option is A

Step 1: Identify the observed ecological pattern. 
Algal species richness is greater in pools that contain grazing snails compared to pools where snails are absent.
This observation indicates that grazing activity is influencing community structure and diversity.

Step 2: Recall the idea of top-down regulation.
Grazers often function as top-down controllers by limiting the abundance of dominant producers.
By suppressing species that would otherwise outcompete others, grazers help maintain a more diverse community.

Step 3: Evaluate option (A).
If snails preferentially consume the most common or dominant algal species, they reduce competitive dominance.
This allows less competitive and rarer species to persist alongside dominant ones.
Such selective grazing is a well-established mechanism for increasing species diversity.
Therefore, option (A) is correct.

Step 4: Evaluate the remaining options.
(B) Snails avoiding algae contradicts the assumption that grazing affects algal composition, so it is incorrect.
(C) Feeding primarily on rare species would further decrease diversity rather than increase it, making it incorrect.
(D) Equal grazing on all species would not specifically suppress dominant species and would be less effective in promoting diversity.

Step 5: Final conclusion.
The higher algal diversity observed in pools with snails is best explained by selective grazing on dominant algal species:

\[ \boxed{(A)} \]