Final answer:
The relationship between the bull's horn acacia tree and the ants is mutualism, where both parties benefit from shelter, food, and protection.
Step-by-step explanation:
The mutual relationship between the bull’s horn acacia tree and the ants that live in its thorns is an example of mutualism. In this interaction, the acacia tree supplies the ants with food in the form of nectar and shelter within its thorns, while the ants defend the tree from herbivores and other potential threats, thus benefiting both species involved. This remarkable example of coevolution between a plant and an animal species showcases how complex and advantageous such biotic interactions can be in nature.