Question

scenario 1:
a population of fish becomes trapped in a lake separated from the ocean. over generations,
they can no longer survive in salt water.
→ explain what type of isolation occurred and why.

Explanation:

Geographic isolation occurs when a physical barrier (here, the separation of the lake from the ocean) divides a population. The fish in the lake are physically separated from the ocean - dwelling fish. Over generations, this separation leads to genetic divergence. Since the lake - trapped fish adapt to the freshwater environment (and lose the ability to survive in saltwater), the physical separation (geographic barrier) is the key factor.

Answer:

Geographic isolation occurred. A physical barrier (the separation of the lake from the ocean) prevented gene flow between the fish population in the lake and the ocean - dwelling fish. Over time, the lake - fish adapted to the freshwater environment (and lost salt - water survival ability) due to this physical separation.