Now you see me, now you don't: Land use and rainfall pulses interact to determine patterns in small mammal diversity in the Kalahari, South Africa

In arid landscapes, primary productivity is prompted by episodic rainfall. The biological productivity response, in arid systems, to a rainfall event is known as a pulse event that results in an instantaneous change in ecological parameters. These pulse events are high-intensity, short-lived events that result in an abundance of resources. Of the mammals, small mammals are often the quickest to respond to these pulse events numerically and behaviourally. Small mammals are vital to overall ecosystem health and have long been recognised as indicators of environmental change. To test the effect of pulse events on small mammal abundance and diversity, we used the Kalahari Desert as a model system. We compared small mammal data from two surveys during a prolonged drought period (March 2019) and after an extremely wet period (March 2021), at Erin Game Farm and Miershooppan Livestock Farm in the Northern Cape, South Africa. We used a combination of camera trap surveys, walking transects, and live trapping transects to record rodent and meso-carnivore diversity and abundance. Both mammal abundance and diversity were relatively equal between land uses during the drought period survey. However, although there was an observable increase in species diversity and abundance in the wet period, for both land uses, the increase in rodent abundance and diversity in the live trap lines, on the livestock farm were much more prominent. This unexpected result could be attributed to differences in land-use history of the two sites, but further investigation is needed to test this hypothesis. The results of this study provide an understanding of how land use may interact with the effect of the irruption of resources, and subsequent rodent and meso-carnivore response, thus providing vital information for the management of arid landscapes.
The first small mammal survey occurred during a period of drought in 2019, from 08 March 2019 to 19 March 2019. The second survey occurred during a period of high rainfall, starting on 25 March 2021, and ended 03 April 2021. Live traps were placed in lines consisting of ten 7.6 cm x 8.9 cm x 22.9 cm Sherman Folding Aluminium traps. The traps were placed approximately 10 m apart from one another in a South to North direction; thereby making 100 m line transects. In addition, on each end of these transects, we placed one 75 cm x 30 cm x 30 cm Standard Humane Cage (SHC) Trap on either end of the transect for the trapping of meso-carnivores. In addition to the traps, the small mammal survey included the daily walking of morning transects with local ‡Khomani San trackers. The observers and trackers were dropped at a different point each day, and walked 1.25 km up from the starting coordinate, 500 m to the right and 1.25 km down thereby resulting in 3 km long transects. Tracks, scat/dung, and visual sightings were observed and recorded. We also performed a camera trap survey with camera traps following the SnapShot Safari protocol.

在干旱景观中，初级生产力（primary productivity）由间歇性降雨触发。在干旱生态系统中，生物生产力对降雨事件的响应被称为脉冲事件（pulse event），该事件会导致生态参数发生瞬时变化。此类脉冲事件属于高强度、短持续时间的事件，可带来资源的大量富集。在哺乳动物类群中，小型哺乳动物通常在种群数量与行为模式上最快响应此类脉冲事件。小型哺乳动物对生态系统整体健康至关重要，且长期以来被视为环境变化的指示物种。为探究脉冲事件对小型哺乳动物种群数量与多样性的影响，本研究以喀拉哈里沙漠（Kalahari Desert）为研究模式系统。我们于南非北开普省的艾琳狩猎农场（Erin Game Farm）与米尔肖潘畜牧场（Miershooppan Livestock Farm）开展了两次调查，分别对应长期干旱期（2019年3月）与极端湿润期（2021年3月），并对比了两次调查获取的小型哺乳动物数据。本研究结合相机陷阱调查（camera trap survey）、步道样线调查与活体诱捕样线调查，记录啮齿类动物与中型食肉动物（meso-carnivore）的多样性及种群数量。在干旱期调查中，两种土地利用类型下的哺乳动物种群数量与多样性均较为接近。不过，尽管两种土地利用类型在湿润期的物种多样性与种群数量均有可观测的提升，但畜牧场的活体诱捕样线中啮齿类种群数量与多样性的增幅更为显著。这一意外结果可能与两个研究点的土地利用历史差异有关，但仍需进一步研究验证该假说。本研究结果阐明了土地利用如何与资源脉冲效应及后续啮齿类、中型食肉动物的响应产生交互作用，可为干旱景观的管理提供关键参考依据。
首次小型哺乳动物调查于2019年干旱期开展，时间为2019年3月8日至2019年3月19日。第二次调查于强降雨期开展，时间为2021年3月25日至2021年4月3日。活体诱捕笼采用谢尔曼折叠铝制诱捕笼（Sherman Folding Aluminium traps），以10个为一组布设诱捕线，单只诱捕笼尺寸为7.6 cm×8.9 cm×22.9 cm。诱捕笼沿南北方向布设，间距约10米，由此形成总长100米的样线。此外，我们在每条样线的两端各布设1个75 cm×30 cm×30 cm的标准人道笼式诱捕器（Standard Humane Cage, SHC），用于捕获中型食肉动物。除诱捕作业外，本次小型哺乳动物调查还包含每日清晨与当地‡科霍马尼·桑族追踪者一同开展的步道样线调查。调查人员与追踪者每日从不同起点出发，先沿起始坐标向北行进1.25公里，再向右横向行进500米，随后向南行进1.25公里，最终形成总长3公里的样线。调查过程中需记录足迹、粪便以及目视观测到的个体。此外，本研究还按照SnapShot Safari规程开展了相机陷阱（camera trap）调查。