What do the carnivores in a grassland ecosystem represent?

The carnivores in a grassland ecosystem represent secondary and tertiary consumers. 

Carnivores in a grassland ecosystem include consumers like snakes, foxes, lions, hyenas, hawks, etc. 

Small carnivores (secondary consumers) like foxes, hyenas, etc eat herbivores (primary consumers) and subsequently become food for bigger carnivores (tertiary consumers) like lions or tigers.