Final answer:
The initial step to investigate the reliance of yellow perch on opossum shrimp is isolating yellow perch from the pond, which allows scientists to control the environment and accurately assess the fish's diet in the absence of this specific prey.
Step-by-step explanation:
The initial step in an investigation to determine the reliance of yellow perch on opossum shrimp as a food source is isolating yellow perch from the pond. This step, indicated as option b, is essential as it establishes a controlled environment to observe the yellow perch's diet in the absence of opossum shrimp. Before analyzing energy transfers, studying trophic level interactions, or determining the population of opossum shrimp, isolating the yellow perch ensures that subsequent observations and conclusions are accurate reflections of the dependency relationship.
Once isolated, the yellow perch can be observed to see if they seek out alternative food sources or exhibit signs of nutritional deficiency. This suggests how vital opossum shrimp are to their diet. From this initial step, scientists can then proceed to analyze the resulting data to understand energy transfers, trophic level interactions, and the broader implications for the ecosystem in question.