Mutualism disruption by an invasive ant reduces carbon fixation for a
foundational East African ant-plant
Invasive ants shape assemblages and interactions of native species, but
their effect on fundamental ecological processes is poorly understood.
In East Africa, Pheidole megacephala ants have invaded monodominant
stands of the ant-tree Acacia drepanolobium, extirpating native ant
defenders and rendering trees vulnerable to canopy damage by vertebrate
herbivores. We used experiments and observations to quantify direct and
interactive effects of invasive ants and large herbivores on A.
drepanolobium photosynthesis over a 2-year period. Trees that had been
invaded for ≥ 5 years exhibited 69% lower whole-tree photosynthesis
during key growing seasons, resulting from interaction between invasive
ants and vertebrate herbivores that caused leaf- and canopy-level
photosynthesis declines. We also surveyed trees shortly before and after
invasion, finding that recent invasion induced only minor changes in
leaf physiology. Our results from individual trees likely scale up,
highlighting the potential of invasive species to alter ecosystem-level
carbon fixation and other biogeochemical cycles.