Oak trees and squirrels is an interesting one. Red oak specifically, acorns only gestate after winter, squirrels store red oak acorns and when they eat them, tend only to eat the top of them since that part contains less tannins. The lower part of the acorn contains the actual germ. So squirrels will often gather and safely store acorns for the winter, then spread them to new location during the summer while allowing them to germinate.