Impact of an invasive alien ant, Wasmannia auropunctata Roger., on a specialised plant-ant mutualism, Barteria fistulosa Mast. and Tetraponera aethiops F. Smith., in a Gabon forest

In tropical West Africa, the ant Tetraponera aethiops obligately inhabits the domatia of Barteria fistulosa trees, aggressively defending the trees from herbivory and pruning off lianas. We compared the occurrence of ants and lianas on B. fistulosa trees in areas of Gabon, where the invasive little fire ant, Wasmannia auropunctata, was absent (uninfested area) and present (infested area). We found that T. aethiops occurred significantly more often in larger B. fistulosa trees, and that occurrence rates were much higher in the uninfested area versus the infested area: on < 1 m trees: 17% vs. 0%; 1-5 m trees: 58% vs. 3%; > 5 m trees: 90% vs. 10%). In contrast, lianas occurred significantly less often in the uninfested area versus the infested area: on < 1 m trees: 0% vs. 100%; 1-5 m trees: 0% vs. 77%; > 5 m trees: 10% vs. 63%). In the infested area, W. auropunctata occurred significantly less often in larger B. fistulosa trees (on < 1 m trees: 100%; 1-5 m trees: 97%; > 5 m trees: 90%). Here T. aethiops and W. auropunctata coexisted on few trees (on < 1 m trees: 0%; 1-5 m trees: 1%; > 5 m trees: 4%). The negative consequences for the trees are already evident, and the situation for native ants is likely to decline further in future because they will not be able to generate the large (relatively resistant) colonies found on large trees.