Final answer:
Ants on acacia trees provide protection from herbivores and pathogens as part of a symbiotic relationship where the trees offer ants shelter and nutritious food rewards.
Step-by-step explanation:
The presence of ants on acacia trees leads to improved plant performance including protection from herbivores and possibly enhanced growth and reproduction. This type of relationship is known as 'protection rackets', where the acacia tree provides food and shelter to ant species such as Pseudomyrmex spp, and in return, the ants defend the tree from herbivores and potential plant pathogens. Acacia trees supply complex food rewards like Beltian bodies, which contain valuable lipids and proteins, and also offer nesting spots in their large thorns, all of which are more costly for the plant to produce. The mutually beneficial relationship extends to aphid-ant interactions, where ants protect aphids in exchange for honeydew, a sugary byproduct of aphid feeding.