Data from: Termite mounds differ in their importance for herbivores across savanna types, seasons and spatial scales

Herbivores do not forage uniformly across landscapes, but select for patches of higher nutrition and lower predation risk. Macrotermes mounds contain higher concentrations of soil nutrients and support grasses of higher nutritional value than the surrounding savanna matrix, attracting mammalian grazers that preferentially forage on termite mound vegetation. However, little is known about the spatial extent of such termite influence on grazing patterns and how it might differ in time and space. We measured grazing intensity in three African savanna types differing in rainfall and foliar nutrients and predicted that the functional importance of mounds for grazing herbivores would increase as the difference in foliar nutrient levels between mound and savanna matrix grasses increases and the mounds become more attractive. We expected this to occur in nutrient-poor areas and during the dry season when savanna matrix grass nutrient levels are lower. Tuft use and grass N and P content were measured along transects away from termite mounds, enabling calculation of the spatial extent of termite influence on mammalian grazing. Using termite mound densities estimated from airborne light detection and ranging (LiDAR), we further upscaled field-based results to determine the percentage of the landscape influenced by termite activity. Grasses in close proximity to termite mounds were preferentially grazed at all sites and in both seasons, but the strength of mound influence varied between savanna types and seasons. In the wet season, mounds had a relatively larger effect on grazers at the landscape scale in the nutrient-poor, wetter savanna, whereas in the dry season the pattern was reversed with more of the landscape influenced at the nutrient-rich, driest site. Our results reveal that termite mounds enhance the value of savanna landscapes for herbivores, but that their functional importance varies across savanna types and seasons.

草食动物并不会在整个景观中均匀觅食，而是会优先选择营养含量更高、被捕食风险更低的区域进行采食。大白蚁（Macrotermes）丘的土壤养分浓度高于周边的稀树草原基质，且其上生长的草本植物营养价值更为出众，因此会吸引哺乳动物植食动物优先在蚁丘植被上觅食。然而，目前学界对于这类白蚁活动对放牧模式的空间影响范围，以及这种影响在时间与空间维度上的差异仍知之甚少。我们在三种降雨条件与叶片养分水平各异的非洲稀树草原生境中测量了放牧强度，并提出假设：蚁丘与稀树草原基质草本的叶片养分水平差异越大，蚁丘的吸引力越强，其对放牧草食动物的功能重要性也就越高。我们预期这种情况会出现在养分贫瘠的区域，以及稀树草原基质草本养分水平更低的旱季。我们沿着远离白蚁丘的样带记录了草丛的采食情况，并测量了草本植物的氮（N）、磷（P）含量，借此计算出白蚁活动对哺乳动物放牧行为产生影响的空间范围。借助机载激光雷达（Light Detection and Ranging，LiDAR）估算的白蚁丘密度，我们进一步将野外观测结果进行尺度上推，以确定受白蚁活动影响的景观占比。在所有样地与两个季节中，靠近白蚁丘的草本植物均被优先采食，但蚁丘影响的强度在不同稀树草原生境与季节间存在差异。在雨季，蚁丘在养分贫瘠且较为湿润的稀树草原生境中，对景观尺度上的放牧者产生的相对影响更大；而在旱季，情况则恰好相反，在养分富足且最为干旱的样地中，受影响的景观占比更高。我们的研究结果表明，白蚁丘能够提升稀树草原景观对草食动物的承载价值，但其功能重要性会随稀树草原生境类型与季节的不同而发生变化。