I suggest checking out A Primer of Ecology by Nicholas Gotelli. It's not meant for high school students, but it has a lot of problems that an advanced high school calculus student could probably handle or you could adapt to bring to their level.
I'd check out Gotelli's Primer: https://www.amazon.com/Primer-Ecology-Nicholas-J-Gotelli/dp/0878933182 . This is useful as an overview of the concept of modeling populations dynamics and landscape diversity. Then, if you want to start heading off into the deep end, look up papers on the topics of co-occurrence networks and zeta diversity.