One recent finding that shows how much we still got to learn about ecosystems and relationship between species: the decline in whales population (due to us hunting them) caused a decline in krill population as well, triggering a butterfly effect in all the ecosystem.
Since although every whale eats literally several tons of krill every day, they also provide the fertilizer for phytoplancton, which feeds the whole ecosystem, including krill.
Turns out whales have a very special role, which I guess it was already easy to imagine before, but it’s bigger than what scientists believed until these findings were made. They now describe whales (in a bit dramatic yet easy to understand way) as “mobile processing plants”. Given the size of those things maybe not so dramatic.