The primary difference between small, controlled lab experiments and ecosystem-scale experiments is the applicability of the results.
Small, controlled lab experiments typically focus on specific variables under tight control, allowing for precise manipulation and observation of cause-and-effect relationships. However, findings from these experiments may not always translate well to real-world situations due to the simplified conditions.
In contrast, ecosystem-scale experiments incorporate a broader range of variables and interactions as they take place in natural settings, providing insights that are more relevant to complex ecological systems. This can enhance the ecological validity of the results, making them more applicable to real-world scenarios.
While the other options (number of variables, species of interest, and abiotic factors) can also differ between the two types of experiments, the applicability of results is the most significant distinction.