Because of an Acorn by Lola M. Schaefer and Adam Schaefer illustrated by Frann Preston-Gannon*

Very simple text reveals how all parts of the ecosystems depend on each other to thrive.  The focused ecosystem in this book is the white oak forest of the Cumberland Plateau.
The illustrations definitely enhance the "story" and give greater meaning to the words.
Strategy: cause/effect
*Highly recommend.
-Borrowed from the library.