Question 1:
The main, or central, idea of the passage is:
Thanks to conservation efforts, Florida manatee populations have increased.
Question 2:
The detail in bold develops the main idea by:
It suggests that the rebound in manatee populations is solely due to natural factors rather than human intervention.
(Note: In this case, none of the provided responses correctly align with the information in the passage. The correct option would emphasize the role of conservation efforts in the rebound of manatee populations, but given the provided choices, the last option is misleading. The appropriate response should reflect that the increase is attributed to human-led conservation efforts.)