Data for manuscript: Beyond mutualism disruption: cascading consequences of big-headed ant invasion on critical forage for African megafauna

Invasive species are disrupting mutualisms, with numerous consequences. Over large areas of East Africa, <i>Vachellia drepanolobium</i> hosts ants that defend the trees against browsing, stabilizing tree cover. Using a large-scale herbivore exclusion experiment over four years, we investigated how the invasive ant <i>Pheidole megacephala</i>, by displacing native ants, affected trees, grasses and nitrogen dynamics in the presence and absence of megabrowsers (elephants, giraffes). Over four years, tree numbers declined by 30% in invaded areas exposed to megabrowsers. Invaded trees produced 50% more new stem growth, but browse production per hectare still declined by 30%. In invaded areas, both trees and grasses showed higher reliance on nitrogen derived from the soil, rather than fixed from the atmosphere, and elevated leaf nitrogen levels, suggesting potential reorganization of nutrient flows. These consequences of invasion threaten the forage supply for large mammalian browsers, but less so grazers, in this region of high conservation importance.