I saw footage when some squirrels (or monkeys) ware picking up something tasty out of the shallow water. They had to be careful because there might have been predators in the water.

If individual spotted predator they yelled and whole pack ran to the trees.

But occasionally weaker individuals yelled even when there was no predator to drive away stronger individuals to get some food himself.

So they altruistically warned each other but there was free-rider in who occasionally abused the altruistic system for personal gain. He couldn't do that too much because other individuals would notice and kick his butt. So altruism and free-riding in nature can be in balance and still give obvious advantage in cooperation.