From what I could gather in my short time here, Karma exists on Lemmy as well, it's just not a public stat and that's great because it completely eliminates the reason for karma whoring.
Sure you could try to add up all the upvotes and deduct your downvotes, but why bother? People trying to raise their karma (or those weirdos who were trying to farm downvotes) were always annoying at best and conversation killers at worst.