With a solid understanding of biology, it's time for the long view - how the living things interact with and influence each other and their environments.
Life is powerful, and in order to understand how living systems work, you first have to understand how they originated, developed and diversified over the past 4.5 billion years of Earth's history.
Population ecology is the study of groups within a species that interact mostly with each other, and it examines how they live together in one geographic area to understand why these populations are different in one time and place than they are in another. How is that in any way useful to anyone ever?
If being alive on Earth were a contest, humans would win it hands down. We're like the Michael Phelps of being alive, but with 250,000 times more gold medals.
Interactions between species are what define ecological communities, and community ecology studies these interactions anywhere they take place. Although inter-species interactions are mostly competitive, competition is pretty dangerous, so a lot of interactions are actually about side-stepping direct competition and instead finding ways to divvy up resources to let species get along.