Answer
By identifying the most likely factors and limiting each one on a different test group, we can do this study.
Work Step by Step
Once the possible variables are identified, the impact of each potential factor can be manipulated on separate test groups and the results can be measured.
Alternately, the factors can be measured throughout the ecosystem in areas with different densities of primary producers. It could be conceivably possible to notice a pattern in one particular factor that is associated with more or less population density of these producers.
