Final answer:
The paramecium population, which reproduces asexually, would be at a disadvantage in changing environmental conditions due to the lack of genetic variation compared to the sexually reproducing fish population.
Step-by-step explanation:
The question concerns the potential disadvantages of asexual reproduction compared to sexual reproduction, particularly in the context of changing environmental conditions in a lake ecosystem where paramecium and fish populations live. When the environmental conditions change, the disadvantage that paramecium, which reproduce asexually, would have over fish, which reproduce sexually, is that paramecium would have less genetic variation in their population. As paramecium reproduce by asexual methods, they produce offspring that are clones of themselves, meaning that the genetic differences in the paramecium population are minimal. This lack of genetic variation can be detrimental in changing environments, as it results in a reduced ability of the population to adapt because all individuals are nearly identical genetically and may not possess or develop beneficial mutations quickly.