Experimental reduction of plant abundance changes interaction frequency of a tri‐trophic micro‐food web: contrasting responses of generalists and specialists. (6th September 2019) - Xi, Xinqiang
Abstract: Species abundance is vulnerable to climate change and anthropogenic impact. Although numerous studies have examined the food web response to species loss, their response (e.g. in network topology and interaction frequency) to changes in species abundance has received little attention. We experimentally reduced the abundance (by c. 60%) of one host plant species ( Saussurea nigrescens ) in a tri‐trophic micro‐food web consisting of two common Asteraceae species ( S. nigrescens and Anaphalis flavescens ), their pre‐dispersal seed predators (tephritid flies) and the parasitoid wasps that feed on these seed predators. The neutral process hypothesis posits that network topology and interaction frequency are determined by the relative abundances of the participating species. Accordingly, we hypothesized that interaction frequency (indicated by the rate of flies infesting plants and of parasitoid wasps parasitizing flies) would decrease with decreasing abundance of host plant abundance. Consistent with the neutral process hypothesis, abundance reduction significantly decreased the rate of generalist flies infesting the manipulated plant host species, but increased the rate on unmanipulated plant species. In contrast, abundance reduction significantly increased the rate of specialist flies infesting the manipulated species, but it had no demonstrable effect on the specialists on the unmanipulated plant host. Moreover, abundance reduction significantly increased the rate of parasitoid wasps (as a species group) parasitizing flies in the manipulated species, but decreased the rate of the unmanipulated species. These results were not attributable to neutral processes, but can be explained by adaptive foraging theory. In addition, experimental manipulation did not shift the qualitative presence–absence of the linkages in the micro‐food web, and the change in the abundance of both fly and wasp species was smaller than the abundance changes of the manipulated plant species. Synthesis . Our results indicate that both neutral processes and/or adaptive foraging likely contributed to food web stability in responses to changes in species abundance. Because species abundance is vulnerable to abiotic and biotic environmental changes, we suggest more research should be conducted to understand how food webs respond to climate change and anthropogenic disturbance. Abstract : Our results show that generalist and specialist herbivores differ in their interaction frequencies with plants under experimental reduction of species abundance. This suggests that adaptive foraging contributes to the maintenance of food web stability. Foreign Language Abstract: 气候变化与人类活动极易改变物种的多度。大量前期研究检验了食物网如何响应物种的丢失, 但物种多度的改变如何影响食物网的结构与链接强度鲜有报道。 我们在青藏高原东缘的高寒草甸上选择了一个由两种菊科植物 （钝苞雪莲, Saussurea nigrescens 和淡黄香青, Anaphalis flavescens ） 以及取食植物种子的实蝇和实蝇的天敌 （寄生蜂） 所构成的微型食物网作为研究对象。 我们人为降低了钝苞雪莲60%的个体, 以检测植物多度变化对该食物网的影响。 根据中性过程理论的预测, 食物网中链接的发生及其强度取决于相互作用的物种的相对多度。据此, 我们预测, 实蝇寄生植物的频率以及实蝇被小蜂寄生的频率会随植物多度的下降而降低。 我们的研究发现, 与中性过程理论一致, 植物多度的下降显著降低了泛化实蝇对钝苞雪莲的寄生概率, 但提高了它们对淡黄香青的寄生概率。相反, 在减少钝苞雪莲的样地中, 特化实蝇对钝苞雪莲的寄生概率显著提高了。减少钝苞雪莲的密度, 并没有改变特化实蝇对淡黄香青的寄生概率。 钝苞雪莲多度的下降还改变了小蜂对钝苞雪莲花序中实蝇幼虫的寄生概率, 降低了小蜂对淡黄香青花序中实蝇幼虫的寄生概率。这些结果并不符合中性过程的预测, 但符合适应性捕食理论的预测。此外, 实验操作并没有改变食物网中链接的出现与否, 实蝇和寄生蜂多度的变化幅度也要显著小于钝苞雪莲的变化幅度。 这些观测结果表明, 中性过程与适应性取食策略共同影响了食物网的稳定性及其对物种多度变化的响应。考虑到物种多度对生物与非生物环境的变化极为敏感, 我们建议开展更多的研究, 以探明气候变化和人类活动所引起的物种多度变化如何影响食物网的稳定性。