What is the main advantage for animals that are at the end of a very short food chain?

There are many of them so that means more are spared.

More energy gained

Explanation:

If the food chain is shorter then more energy is left behind for the last consumer. So lesser prey needs to be hunted and more digestible food material is found. But if it is a long food chain the last consumers receive an extremely small amount of energy from each prey and more of inedible waste such as bones and shin will be found