Estación Experimental de Zonas Áridas, Functional and Evolutionary Ecology, Consejo Superior de Investigaciones Científicas (CSIC), Almería, Spain.
Research Unit of Biodiversity (UO/CSIC/PA), Oviedo University, Mieres, Spain.
J Anim Ecol. 2020 Feb;89(2):334-346. doi: 10.1111/1365-2656.13101. Epub 2019 Sep 26.
Shifts in densities of apex predators may indirectly affect fundamental ecosystem processes, such as decomposition, by altering patterns of cascading effects propagating through lower trophic levels. These top-down effects may interact with anthropogenic impacts, such as climate change, in largely unknown ways. We investigated how changes in densities of large predatory arthropods in forest leaf-litter communities altered lower trophic levels and litter decomposition. We conducted our experiment in soil communities that had experienced different levels of long-term average precipitation. We hypothesized that altering abundances of apex predators would have stronger effects on soil communities inhabiting dry forests, due to lower secondary productivity and greater resource overexploitation by lower trophic levels compared to wet forests. We experimentally manipulated abundances of the largest arthropod predators (apex predators) in field mesocosms replicated in the leaf-litter community of Iberian beech forests that differed in long-term mean annual precipitation by 25% (three dry forests with MAP < 1,250 mm and four wet forests with MAP > 1,400 mm). After one year, we assessed abundances of soil fauna in lower trophic levels and indirect impacts on leaf-litter decomposition using litter of understorey hazel, Corylus avellana. Reducing densities of large predators had a consistently negative effect on final abundances of the different trophic groups and several taxa within each group. Moreover, large predatory arthropods strongly impacted litter decomposition, and their effect interacted with the long-term annual rainfall experienced by the soil community. In the dry forests, a 50% reduction in the densities of apex predators was associated with a 50% reduction in decomposition. In wet forests, the same reduction in densities of apex soil predators did not alter the rate of litter decomposition. Our results suggest that predators may facilitate lower trophic levels by indirectly reducing competition and resource overexploitation, cascading effects that may be more pronounced in drier forests where conditions have selected for greater competitive ability and more rapid resource utilization. These findings thus provide insights into the functioning of soil invertebrate communities and their role in decomposition, as well as potential consequences of soil community responses to climate change.
顶级掠食者密度的变化可能会通过改变低级营养级的级联效应模式，间接影响基本的生态系统过程，如分解。这些自上而下的影响可能以未知的方式与人为影响（如气候变化）相互作用。我们研究了森林叶层群落中大型捕食性节肢动物密度的变化如何改变低级营养级和凋落物分解。我们在经历不同长期平均降水量的土壤群落中进行了实验。我们假设，由于与湿林相比，低营养级的次级生产力较低，资源过度开发更为严重，因此改变顶级掠食者的丰度对干林土壤群落的影响会更大。我们在不同长期平均年降水量（25%）的伊比利亚山毛榉森林叶层群落中，通过田间中尺度实验操纵最大节肢动物捕食者（顶级捕食者）的丰度。三个干林的长期平均年降水量<1,250mm，四个湿林的长期平均年降水量>1,400mm。一年后，我们使用下层榛树（ Corylus avellana ）凋落物评估了较低营养级的土壤动物丰度和对凋落物分解的间接影响。减少大型捕食者的密度对不同营养级和每个营养级内的几个分类群的最终丰度都有一致的负面影响。此外，大型捕食性节肢动物对凋落物分解有强烈的影响，而且它们的作用与土壤群落经历的长期年降雨量相互作用。在干林中，减少 50%的顶级捕食者密度与分解减少 50%相关。在湿林中，顶级土壤捕食者密度减少相同幅度并不会改变凋落物分解的速率。我们的结果表明，捕食者可能通过间接减少竞争和资源过度开发来促进低级营养级，在干旱森林中，这种级联效应可能更为明显，因为在干旱森林中，条件已经选择了更强的竞争能力和更快速的资源利用。这些发现为了解土壤无脊椎动物群落的功能及其在分解中的作用，以及土壤群落对气候变化的反应的潜在后果提供了线索。
