Morris Timothy, Letnic Mike
Centre for Ecosystem Science, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales 2052, Australia.
Centre for Ecosystem Science, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales 2052, Australia
Proc Biol Sci. 2017 May 17;284(1854). doi: 10.1098/rspb.2017.0111.
It is widely assumed that organisms at low trophic levels, particularly microbes and plants, are essential to basic services in ecosystems, such as nutrient cycling. In theory, apex predators' effects on ecosystems could extend to nutrient cycling and the soil nutrient pool by influencing the intensity and spatial organization of herbivory. Here, we take advantage of a long-term manipulation of dingo abundance across Australia's dingo-proof fence in the Strzelecki Desert to investigate the effects that removal of an apex predator has on herbivore abundance, vegetation and the soil nutrient pool. Results showed that kangaroos were more abundant where dingoes were rare, and effects of kangaroo exclusion on vegetation, and total carbon, total nitrogen and available phosphorus in the soil were marked where dingoes were rare, but negligible where dingoes were common. By showing that a trophic cascade resulting from an apex predator's lethal effects on herbivores extends to the soil nutrient pool, we demonstrate a hitherto unappreciated pathway via which predators can influence nutrient dynamics. A key implication of our study is the vast spatial scale across which apex predators' effects on herbivore populations operate and, in turn, effects on the soil nutrient pool and ecosystem productivity could become manifest.
人们普遍认为，处于低营养级的生物，尤其是微生物和植物，对于生态系统的基本服务（如养分循环）至关重要。从理论上讲，顶级食肉动物对生态系统的影响可能会通过影响食草作用的强度和空间组织，进而扩展到养分循环和土壤养分库。在此，我们利用对澳大利亚斯特雷泽莱茨沙漠中穿越防野狗围栏的野狗数量进行的长期操控，来研究去除顶级食肉动物对食草动物数量、植被和土壤养分库的影响。结果表明，在野狗稀少的地方袋鼠数量更多，并且在野狗稀少的地方，排除袋鼠对植被以及土壤中的总碳、总氮和有效磷的影响显著，但在野狗常见的地方则可忽略不计。通过表明顶级食肉动物对食草动物的致死效应所引发的营养级联反应会延伸至土壤养分库，我们证明了一条此前未被重视的途径，即食肉动物可通过此途径影响养分动态。我们研究的一个关键意义在于，顶级食肉动物对食草动物种群产生影响的空间尺度极为广阔，进而对土壤养分库和生态系统生产力产生的影响可能会显现出来。
