Ungulate geophagy maintains termite mound habitat heterogeneity and increases internal mound temperature

Savannas are globally important ecosystems and unique in supporting abundant and diverse populations of wild large mammals. Mound building fungus-farming Macrotermitinae are key determinants of savanna structure and function. Termite colonies are sensitive to shade, and their lifetime reproductive success is substantially reduced in forests compared to open savanna areas. Here we experimentally show how ungulates, predominantly impala modify mound soil and vegetation cover and consequently internal temperature in Macrotermes subhyalinus epigeal nests. There are large differences in soil nutrient concentrations between the eastern and western termite mound sector. Ungulates selectively feed on the eastern side of the mounds, reducing vegetation cover and exposing that sector to the warming morning sun. Soil sodium concentration, an essential nutrient for heterotrophs is high on the eastern open mound sector on termite mounds. Important plant nutrients are accumulated on the western side of mounds, facilitating growth of vegetation that shade mounds from the hot afternoon sun. When excluding large herbivores from mounds by fencing, differences in sodium soil concentrations between the eastern and western side of the mound are no longer evident while other soil concentration differences are less pronounced. Following fencing, trees gradually established on the eastern side and eventually mounds were completely covered by trees. Shading arising from ungulate exclusion reduce internal mound temperature by 1.6 degrees, resulting in sub-optimal conditions for termite colonies. This study reveals unknown relationships between key functional groups in tropical savannas. The abundance of large iconic wild herbivores is declining over large African savanna areas. Reduced ungulate populations could in turn lead to sub-optimal conditions for Macrotermes termites with subsequent adverse consequences for litter decomposition and plant and animal diversity across African savannas.