Complex sentence: Birds are unaffected by the natural chemicals contained in the berries (see below), and eat them, scattering the seeds, though they are also found adventitiously in commercial seed (e.g., vegetable seed packets).
Split into simpler sentences: Birds are unaffected by the natural chemicals contained in the berries (see below), and eat them, dispersing the seeds. Seed are also found in commercial seed (e.g., vegetable seed packets).