Answer: ecological niche
Explanation:
An ecological niche can be define as the functional role that an organism plays in an ecosystem during the coarse of it's life. Like, the type of food chosen for eating, type of habitat chosen, season for breeding, predator- prey relationship, harm and benefit it provides to other species and others.
The acacia tree provides a habitat and protection to the ants these are the functional roles the acacia tree plays in an ecosystem. Therefore, this defines the ecological niche of the acacia tree in an ecosystem.
