Final answer:
The studies by Power and colleagues demonstrated that species interactions can vary depending on the environmental context, and highlighted the importance of trophic facilitation and sampling effort in determining species diversity estimates.
Step-by-step explanation:
The studies by Power and colleagues of northern California river ecosystems demonstrated that the strengths of species interactions can vary depending on the environmental context. They also showed the importance of trophic facilitation, where different species improve environmental conditions for each other. Additionally, they found that species diversity estimates can vary depending on the sampling effort.