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，初级生产力由间歇性降雨驱动。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），这类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、短持续时长的事件，可带来大量资源供给。在哺乳动物类群中，小型哺乳动物往往在种群数量与行为层面最快响应这类脉冲事件。小型哺乳动物对维持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丰度与多样性的影响，本研究以喀拉哈里沙漠（Kalahari Desert）为模式系统。我们在南非北开普省的艾琳狩猎农场（Erin Game Farm）与米尔朔潘畜牧农场（Miershooppan Livestock Farm），分别于长期干旱期（2019年3月）与极端湿润期（2021年3月）开展两次调查，并对比了两次调查的小型哺乳动物数据。

本研究结合相机陷阱调查、步行样线调查与活体诱捕样线调查，记录了啮齿类与中型食肉动物（meso-carnivore）的多样性与丰度。干旱期调查结果显示，两种土地利用类型下的哺乳动物丰度与多样性均较为相近。但在湿润期，两种土地利用类型的物种多样性与丰度均出现可观测的提升；其中畜牧农场的活体诱捕样线中，啮齿类的丰度与多样性提升更为显著。这一意外结果或与两个样地的土地利用历史差异相关，但仍需进一步研究验证该假说。

本研究结果有助于理解土地利用如何与资源脉冲效应相互作用，以及后续啮齿类与中型食肉动物的响应机制，可为干旱景观的管理提供关键参考信息。

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，起始时间为2021年3月25日，结束于2021年4月3日。

活体诱捕采用规格为7.6 cm × 8.9 cm × 22.9 cm的谢尔曼折叠铝制诱捕笼（Sherman Folding Aluminium traps），以10 m的间距沿南北方向布设，形成总长100 m的样线。此外，在每条样线的两端各放置1个规格为75 cm × 30 cm × 30 cm的标准人道诱捕笼（Standard Humane Cage Trap，SHC Trap），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晨间步行样线调查，由当地‡科曼尼桑族追踪者参与。调查团队每日在不同点位出发，从起始坐标向北行进1.25 km，再向右行进500 m，随后向南行进1.25 km，最终形成总长3 km的样线。调查人员会记录观测到的足迹、粪便与视觉目击个体。

本研究同时遵循SnapShot Safari协议开展了相机陷阱调查。