A researcher wants to study the effect of habitat fragmentation on bird species richness in a tropical rainforest. The species richness of the same rainforest before fragmentation is known. The best study design to ensure valid and reliable results would be to:

• Correct answer
  A

  compare bird species richness in multiple patches of varying sizes of the entire tropical rainforest.
• B

  count the number of bird species in a single large patch of the tropical rainforest.
• C

  compare bird species richness of the fragmented tropical rainforest with that of a fragmented temperate forest.
• D

  compare the total number of individuals of any bird species in the fragmented and unfragmented tropical rainforest.

Hence, the correct answer is option: 'A'.