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

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 <i>Trinervitermes trinervoides</i> (Isoptera: Termitidae) mounds in the Karoo (South Africa) within an exclosure and continuously-grazed plot from a &gt;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.

地表白蚁（Epigeal termites）通过觅食与筑丘活动改变生态系统尺度的生态过程，其影响强度与白蚁种群密度呈正相关。尽管学界已对自然生境中影响白蚁丘密度的诸多因素开展了大量研究，但白蚁对家畜放牧的响应机制仍未得到足够关注。本研究依托一项开展超75年的放牧定位实验，对比了南非卡鲁（Karoo）地区围栏禁牧区与长期连续放牧样地内三点叉白蚁（*Trinervitermes trinervoides*，等翅目：白蚁科）的蚁丘特征与密度。具体而言，本研究旨在明确长期家畜放牧是否会对以下4项指标产生影响：(1) 白蚁丘的密度、体积、基面积与粒径大小；(2) 蚁丘的占用情况与筑丘年龄；(3) 植被特征；(4) 土壤理化性质。研究结果显示，长期放牧使蚁丘密度提升了一倍。与此同时，平均蚁丘粒径有所减小，但最大蚁丘的尺寸与蚁丘粒径分布范围均有所扩大，且年轻活跃蚁丘的占比与数量均出现上升。不过，上述变化并未改变景观尺度下蚁丘的总基面积与总体积。长期放牧未对植被特征产生显著影响，但会导致土壤中的磷、镁与钙元素发生耗竭。本研究推测，家畜放牧可通过凋落物破碎与粪便产出为白蚁提供额外的觅食资源，进而促进蚁丘的新建与种群密度提升，同时也能使部分蚁丘达到更大的最大尺寸。