Plants produce bitter alkaloids as an anti-feedant defense mechanism against herbivores.

“So plants produce chemical defense all the time. Right? The alkyoids are by the way bitter compounds by nature. So most of the time they're anti-feedant to make sure that the passing by uh deer, giraffe, whatever is not going to eat all the leaves off of that tree. They're going to have a couple and realize this is nasty. I don't want to do this. I'm going to move on to the next plant.”