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   Location:Home > Research > Research Progress
Spiders have important trophic cascade effects on forest-floor food webs in Xishuangbanna
Author: Liu Shengjie
ArticleSource: XTBG
Update time: 2014-11-14
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In tropical forest floors, spiders are major predators with high diversity. Macrothele yunnanica(Macrothele, Hexathelidae) is a dominant spider with regard to biomass and density in the tropical forest floor of Xishuangbanna, southwest China . The presence of M. yunnanica may influence the activity and density of prey species. Previous studies found that increasing spider predation decreased densities of Entomobrya, and thus inhibited litter decomposition. Few studies have investigated the effect of web-building spider predation on the soil fauna community in tropical forests.

 Prof. YANG Xiaodong and his colleagues of Xishuangbanna Tropical Botanical Garden (XTBG) manipulated densities of the dominant web-building spider M. yunnanica in a tropical secondary forest floor. They wanted to understand the effects of M. yunnanica density on soil fauna in tropical forest floor and the potential trophic cascade effects of M. yunnanica on rate of leaf litter decomposition. Moreover, the further trophic cascade effects of M. yunnanica on microbial biomass carbon and nitrogen were studied.

   The researchers established thirty plots (1 × 1 m) with 60-cm high external fences in the tropical secondary forest in XTBG. Then they randomly assigned those plots to one of three spider density treatments which included zero spider: where all spiders were removed from these plots; six spiders (natural density): where 6 adult Myunnanica spiders were maintained in the plots and this density is similar with its mean density in this study site; Ten spiders: where 10 adult Myunnanica spiders were kept in the plots. 

To evaluate rate of litter disappearance, the researchers employed the litter bag technique. To determine the initial density of soil fauna in the plots, they collected litter samples from each plot before the spiders were added. To estimate soil microbial biomass carbon and nitrogen, they randomly collected three soil cores (50 mm diameter, 100 mm depth) from each plot at the beginning and end of experiment.

In the study, the researchers demonstrated that predators have important trophic cascade effects on forest-floor food webs. Increased spider abundance most likely enhanced the sign of spider-initiated trophic cascades by decreasing the density of related soil fauna in the tropical secondary forest in Xishuangbanna. While high predator density reduced both macrofaunal (Coleoptera) and mesofaunal (Entomobrya) activity densities, the trophic cascade was only recorded in fine mesh. But changes in spider densities had no cascading effects on microbial biomass.

Trophic interactions in detritus-based food webs can influence ecosystem functioning such as litter decomposition. In consequence, understanding the cascading effects is critical to predicting the dynamic of detritus-based food webs in tropical forest-floor ecosystems.

 The study entitled “Trophic cascade of a web-building spider decreases litter decomposition in a tropical forest floor” has been published online in European Journal of Soil Biology.

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Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences. Menglun, Mengla, Yunnan 666303, China
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