Species → Whistling-thorn ant
Whistling-thorn ant
Crematogaster mimosae
What if it disappeared?
Impact ModerateIf the whistling-thorn acacia's mutualist ant loses its dominant position to a non-protective rival ant, the trees it occupied suffer twice the mortality and more attacks from boring beetles — this is already observed where experimental exclusion of large herbivores (elephant, giraffe) reduces, over ten years, the nectar and swollen-thorn housing the acacia offers its protector ant, making it more vulnerable to this rival.
DocumentedDetail
Palmer, T.M., Stanton, M.L., Young, T.P., Goheen, J.R., Pringle, R.M. & Karban, R. (2008). Breakdown of an ant-plant mutualism follows the loss of large herbivores from an African savanna. Science, 319(5860), 192–195.
The whistling-thorn acacia "pays" its protector ant in nectar and housing hollowed out in its swollen thorns, in exchange for active defense against herbivores. Without browsing pressure, the tree reduces this investment — but the mutualist ant, which depends on this reward to thrive, is then displaced by an opportunistic ant that does not defend the tree as effectively against its real threats (boring beetles). It was the Kenya Long-term Exclosure Experiment that made it possible to isolate this effect over ten years.
If this same mutualism breakdown occurs wherever populations of large herbivores like the elephant genuinely decline (and not just under controlled experimental exclusion), the loss of the protector ant could amplify acacia mortality beyond what the loss of browsing alone would explain — but this remains to be confirmed outside the original experimental site.
ExtrapolatedDetail
Extrapolation à partir de Palmer et al. 2008, combinée aux données de déclin réel de l'éléphant de savane (voir la fiche éléphant de savane).
Palmer et al.'s experiment artificially controls herbivore presence on a plot; it does not measure whether the same pattern occurs in areas where elephants are declining for real-world reasons (poaching, habitat loss) rather than through experimental exclusion.
What's missing to confirm it: A replication of the exclusion experiment at other whistling-thorn savanna sites, along with monitoring over timescales longer than ten years, would confirm whether this mutualism breakdown generalizes wherever large herbivores are genuinely declining.
Documentation
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Palmer et al. (2008) — Breakdown of an ant-plant mutualism follows the loss of large herbivores from an African savanna, Science
Accessed August 7, 2026
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AntWiki — Crematogaster mimosae, répartition et écologie
Accessed August 7, 2026
Last verified: August 14, 2026