Theoretical and accumulating empirical evidence both suggest that functional redundancy among species may limit the strength of trophic cascades (the indirect effects of predators on non-adjacent trophic levels). However, very little is known about functional redundancy impacts on trophic cascades in detritus-based food webs, especially in tropical soil ecosystems.
Prof. YANG Xiaodong and his team of Xishuangbanna Tropical Botanical Garden (XTBG) manipulated the densities of Macrothele yunnanica, a web-building spider species dominant with regard to biomass and density in the tropical forest floor of Xishuangbanna, southwest China. They attempted to illustrate direct effects of M. yunnanica density on different Collembola species in a tropical forest floor and the trophic cascade effects of M. yunnanica on litter decomposition rates. They also wanted to see the role of functional redundancy within Collembola group in mediating cascading effects of M. Yunnanica.
The experiment including three spider density treatments was conducted for one year in fenced plots (1 × 1 m) in Xishuangbanna tropical secondary forest. One was spiders excluded where all spiders were removed from those plots. The other two were six spiders (natural density) and ten spiders (high density) where six or ten adult  M.yunnanica spiders were maintained in the plots respectively.
The researchers found that the annual mean decomposition rate (K value) across the three spider treatments was not significantly different, indicating that spider treatments had no cascading effects on decomposition. Although community composition changed throughout the course of the experiment, litter decomposition was not affected by those changes. 
The study showed that although spider treatments changed Collembola community composition, those changes did not cascade into changes in litter decomposition in litter bags with coarse mesh (2 mm), which was consistent with functional redundancy. The results supported the hypothesis that functional redundancy among Collembola species may weaken the strength of spider-initiated cascading effects. Consequently, changes in Collembola diversity occupying the same trophic level may not significantly alter ecosystem function in tropical forest-floor ecosystems.
The study entitled “Functional redundancy dampens the trophic cascade effect of a web-building spider in a tropical forest floor” has been published online in Soil Biology and Biotechnology.

Contact
YANG Xiaodong, Principal Investigator
Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China
Tel: 86-691-8713236
E-mail: yangxd@xtbg.ac.cn