Data from: Indirect effects of habitat disturbance on invasion: nutritious litter from a grazing resistant plant favors alien over native Collembola

Biological invasions are major threats to biodiversity, with impacts that may be compounded by other forms of environmental change. Observations of high density of the invasive springtail (Collembola), Hypogastrura manubrialis in heavily grazed renosterveld vegetation in the Western Cape, South Africa, raised the question of whether the invasion was favored by changes in plant litter quality associated with habitat disturbance in this vegetation type. To examine the likely mechanisms underlying the high abundance of H. manubrialis, cages with three types of naturally occurring litter with different nutrient content were placed out in the area and collected after different periods of time. Hypogastrura manubrialis was mainly found in the nutrient-rich litter of the yellowbush (Galenia africana), which responds positively to disturbance in the form of overgrazing. This suggests that invasion may have been facilitated by a positive interaction with this grazing resistant plant. By contrast, indigenous Collembola were least abundant in yellowbush litter. Negative correlations between high abundance of H. manubrialis and the abundance and diversity of other species suggest that competitive interactions might underlie low abundance of these other species at the patch level. Group behavior enables H. manubrialis to utilize efficiently this ephemeral, high quality resource, and might improve its competitive ability. The results suggest that interactions among environmental change drivers may lead to unforeseen invasion effects. H. manubrialis is not likely to be very successful in un-grazed renosterveld, but in combination with grazing, favoring the nutrient-rich yellowbush, it may become highly invasive. Field manipulations are required to fully verify these conclusions.生物入侵是生物多样性面临的主要威胁之一，其生态影响可能因其他类型的环境变化而进一步加剧。科研人员在南非西开普省重度放牧的雷诺斯韦尔德植被（renosterveld）中，观测到入侵性弹尾虫（springtail，Collembola）Hypogastrura manubrialis种群密度极高，由此提出疑问：此类入侵是否得益于该植被类型中伴随栖息地扰动产生的植物凋落物品质改变？为探究Hypogastrura manubrialis种群高丰度的潜在机制，研究人员在该区域布设了三种天然凋落物样笼，各凋落物养分含量各不相同，并于不同时段后回收样笼。Hypogastrura manubrialis主要富集于黄灌木（yellowbush，Galenia africana）的富养分凋落物中，而该植物会对过度放牧引发的栖息地扰动呈现正向响应。这表明，此类入侵或通过与这种耐放牧植物的正向互作得以促进扩散。与之形成对照的是，本土弹尾纲物种在黄灌木凋落物中的丰度最低。Hypogastrura manubrialis的高丰度与其他物种的丰度及多样性呈显著负相关，这提示竞争互作或是斑块尺度上其他物种丰度偏低的潜在原因。集群行为使得Hypogastrura manubrialis能够高效利用这类短时存在的优质资源，进而可能提升其竞争优势。研究结果显示，环境变化驱动因子之间的相互作用，可能产生难以预见的入侵效应。Hypogastrura manubrialis在未受放牧的雷诺斯韦尔德植被中未必能取得显著的入侵成功，但在放牧与促进富养分黄灌木生长的双重作用下，其或可成为极具入侵性的物种。仍需开展野外操控实验以充分验证上述结论。