Long-term livestock grazing increases the recruitment success of epigeal termites: insights from a >75-year grazing experiment in the Karoo, South Africa

Abstract

Epigeal termites alter ecosystem-level processes through foraging and mound building. These effects are proportional to density. Whilst much is known about the factors influencing mound density in natural settings, how termites respond to livestock grazing has been overlooked. We compared the characteristics and density of Trinervitermes trinervoides (Isoptera: Termitidae) mounds in the Karoo (South Africa) within an exclosure and continuously-grazed plot from a >75-year grazing experiment. Specifically, we asked whether long-term livestock grazing impacted (1) termite mound density, volume, basal area and size, (2) mound occupancy and age, (3) vegetation characteristics and (4) soil properties. Long-term grazing increased mound density two-fold. This was coupled with a decrease in mean mound size, an increase in the size of the largest mounds and range of mound sizes, and an increase in the proportion and numbers of young, active mounds. However, these changes did not alter landscape-scale mound basal area or volume. Vegetation was unaffected by long-term grazing but it did cause soil phosphorus, magnesium and calcium depletion. We suggest that livestock grazing provides additional forage resources for termites through litter breakup and dung production, leading to greater mound recruitment and thus densities, whilst allowing mounds to achieve greater maximum size.

Keywords: coexistence, ecosystem function, soil nutrients, Trinervitermes trinervoides, vegetation dynamics