Bottom-up effects of aboveground biota, invasive species and drought on soil animal communities

  • Marco Ilardi

Student thesis: Doctoral ThesisDoctor of Philosophy


Soil ecosystems are facing the threat of a growing human population and the consequent global changes. Soil food webs are being exposed to unprecedented levels of disturbance, with the potential to disrupt the regulating interactions between soil biota components, and the role these components play in maintaining the stability of terrestrial ecosystems.

This thesis investigates the response of soil animal communities to disturbances, focusing on perturbations originating above-ground and exerting their primary impact on the resources entering the system, with reverberating effects throughout the soil decomposer food web (bottom-up perturbation).

The perturbations were applied through experimental manipulations, in order to investigate the disturbance in a controlled manner and detect the effects on soil microarthropods and nematodes. Changes in their abundance, taxonomic assemblage and/or trophic response indicate the extent of the disturbance effect and the roles these animals play as regulators of the whole soil food web. Specifically, this research investigated the response of microarthropods and nematodes to nutrients input alterations.

The first two experiments focused on soil microarthropods, which were exposed to resource input manipulation in the form of carrion decomposition (and the associated role of carrion beetles), and an invasive leaf litter shredder (lawn shrimp) at varying leaf litter densities. The impact of extreme drought on nematodes and microarthropods was examined in a field experiment, pairing drought simulation with grassland association manipulation.

Multiple responses were observed across the experiments, ranging from changes in community assemblage to shifts in the trophic structure. In particular, fungal feeding microarthropods (Collembola and various Oribatid mite species) and fungivorous nematodes increased in abundance, leading to the formulation of a novel hypothesis: bottom-up perturbations alter the balance of energy channels in the soil food web by increasing the ratio between fungi and bacteria, thereby altering the regulating role that soil animals exert on these channels.
Date of AwardJul 2020
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsNorthern Ireland Department for the Economy
SupervisorTancredi Caruso (Supervisor), Mark Emmerson (Supervisor) & Jaimie Thomas Allan Dick (Supervisor)

Cite this