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Species of predaceous beetle (top: Agonum impressum) and large (middle: Pheretima aspergillum) and small earthworms (bottom: Aporrectodea nocturna) used to quantify the direct effects of predation on earthworm density and behavior, and indirect effects of predation on soil properties and above-ground plant biomass.

Zhao, C., Griffin, J., Wu, X. & Sun, S. (2013) Predatory beetles facilitate plant growth by driving earthworms to lower soil layers. Journal of Animal Ecology, 82, 749758.

Theory suggests that predators in detritus-based food webs should negatively influence plants, through direct effects on plant-facilitating detritivores. In a three-level food web of predaceous beetles, earthworms and plants, Zhao et al. (2013) report evidence to the contrary. They found that predators drove positive indirect effects on both plant-facilitating soil properties and above-ground plant biomass and that these positive effects were driven by predator-mediated vertical shifts in detritivore habitat use. Their study reinforces the importance of trait-mediated indirect interactions across both ‘green’ and ‘brown’ trophic cascades and emphasizes that understanding the spatial dimension of trophic cascade mechanisms remains a critical research priority.