Since most meerkats “mobs” have only a single dominant pair reproducing, they have eating (or growing) contests to establish who is the next dominant female in the hierarchy. – WTF Fun Facts
Source: https://www.mnn.com/earth-matters/animals/blogs/meerkats-settle-rivalries-eating-contests
In a group of clownfish, there is only one female who is at the top of a strict hierarchy. Only two clownfish in a group reproduce through external fertilization. They are also hermaphrodites, so when the female dies, the largest and most dominant male becomes a female. – WTF Fun Facts
Source: https://en.wikipedia.org/wiki/Amphiprioninae