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 ecological pattern.
Algal diversity is higher in pools with grazing snails than in pools without snails.
This suggests that grazing is playing a role in maintaining or enhancing species diversity.
Step 2: Recall the concept of top-down control.
Grazers can act as top-down regulators by reducing the dominance of competitively superior species.
When dominant species are suppressed, less competitive species can persist, increasing overall diversity.
Step 3: Analyze option (A).
If snails feed preferentially on the more abundant (dominant) algal species,
they prevent competitive exclusion and allow rarer species to coexist.
This mechanism is well-known to increase species diversity.
Hence, (A) is correct.
Step 4: Analyze other options.
(B) Snails avoiding algae contradicts the premise of grazing effects. Incorrect.
(C) Feeding only on rare species would further reduce diversity. Incorrect.
(D) Equal feeding on all species would not specifically reduce dominance and is less effective at maintaining high diversity. Incorrect.
Step 5: Conclusion.
Higher algal diversity in the presence of snails is best explained by selective grazing on dominant species: \[ \boxed{(A)} \]