Wind energy because it's natural and some places dont have electricity.
To be honest, since we live on Earth (assuming you do as well), Earth is the easiest planet to study. We don't know much about the other planets because we've never been to any of them. I believe that the second easiest planet to study is either Uranus or Saturn.
Predator and prey populations affect each other because if a predator of one prey kills that one animal than that animal dies and the prey decrease by one and when one predator dies from being killed or just naturally dying, then the predators decrease by one.
I don’t see any labels, but remember that humans are a great example of a k-selected species. High rates of parental care leads to high survivorship of offspring, and thus negates the need to have large amounts of offspring.
R-selected species are quite the opposite. They produce large amounts of offspring at many intervals in an attempt to maximize survivorship, as they don’t have strong parental involvement with their young. Think of insects.
Forssoic science investigate department