Quantifying nutrient re-distribution from nutrient hotspots using camera traps, indirect observation and stable isotopes in a miombo ecosystem, Tanzania

Abstract

Nutrient hotspots strongly attract mammalian herbivores in nutrient-poor habitats such as savanna systems. However, little is known about their seasonal importance for mammalian herbivore species, particularly grazers. In addition, no study has fully quantified the potential re-distribution of nutrients into the surroundings of these hotspots. We assessed nutrient hotspot (i.e., grazing lawns and termite mounds) use by herbivores in a Miombo ecosystem of the Issa valley, Tanzania, using dung counts, camera traps and stable isotope analyses over a one year period, from May 2016 to October 2017. We conducted dung counts along four transects each radiating away from ten termite mounds and six grazing lawns as well as in 16 control sites 100 m away from each nutrient hotspot. In addition, we sprayed grasses around five termite mounds with urea and traced the isotopic signature back in grazing herbivore dung. Grazer dung deposition was twice as high in hotspot areas vs control sites. A total of 32 camera stations recorded 244 wildlife encounters, with mammalian herbivores using hotspot areas four times more frequently compared to control plots. Stable isotope analyses highlighted that dung deposited by mammalian grazers around hotspots likely originated from grasses within or close to hotspot areas, indicating that grazers are responsible for maintaining nutrient stability of these hotspots. We, therefore, emphasize the importance of grazing mammal species for the long-term persistence of hotspots and, thus, their contribution to the maintenance of a heterogeneous landscape within the Miombo ecosystem.