Symbiosis
In the Central American Acacia sphaerocephala, Acacia cornigera, and Acacia collinsii (collectively known as the bullthorn acacias), the large thorn-like stipules are hollow and afford shelter for several species of Pseudomyrmex ants, which feed on a secretion of sap on the leaf-stalk and small, lipid-rich food-bodies at the tips of the leaflets called Beltian bodies. In return, the ants add protection to the plant against herbivores. Some species of ants will also fight off competing plants around the acacia, cutting off the offending plant's leaves with their jaws and ultimately killing it. Other associated ant species appear to do nothing to benefit their hosts.
Similar mutualisms with ants occur on Acacia trees in Africa, such as the Whistling Thorn acacia. The acacias provide shelter for ants in the hollow stipules and nectar in extrafloral nectaries for their symbiotic ants such as Crematogaster mimosae. In turn, the ants protect the plant by attacking large mammalian herbivores and stem-boring beetles that damage the plant.
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