Food webs can be conceptualized as being powered by energy derived from living and dead vegetation, respectively. Most food web research has focused on “green food webs” which begin with the consumption of living vegetation by herbivores. However, “brown food webs” which stem from the consumption of senescent vegetation by detritivores are also an important channel of energy transfer. In theory, herbivores have the potential to disrupt brown food webs by consuming plant material before it can senesce and become available for detritivores. Here we investigate the effects that grazing by kangaroos, whose population had irrupted partly due to the absence of an apex predator, has on the brown food web in an arid environment. We compared the cover of living and dead vegetation, the abundances of detritivorous termites and their predators inside one ha herbivore exclosures and nearby control plots. Results show there was more cover of living and dead vegetation inside the exclosures. Similarly, abundances of termites and small vertebrate predators of termites were greater inside the exclosures. Our study provides evidence that consumption of plant material by irruptive herbivores can disrupt the functioning of the brown food web by reducing the flow of energy from plant biomass to termites which in turn translates to reduced abundances of termites and small vertebrates that feed on termites. Our findings have implications for conservation and management because they shed light on a previously unconsidered threat to the functioning of arid ecosystems, disruption of brown food webs by irruptive herbivores.
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The data and the R code used to analyse the data have been made available on a Dryad repository: https://doi.org/10.5061/dryad.gb5mkkwt6.
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This study was funded by Nature Foundation SA and the Australian Research Council (DP180101477, LP210100300). We acknowledge the Adnyamathanha and Wilyakali people as the Traditional Owners of Boolcoomatta. We thank the manager of Boolcoomatta reserve, Kurt Tschirner, for facilitating our stays on the reserve. We also thank Matthew Brun and Emma Snare for help with the data collection. This research was conducted under the scientific permit number M27045-1 provided by Department of Environment and Water of the South Australia Government. Ethics approval (20/145A) was obtained through the Animal Care and Ethics Committee at the University of New South Wales.
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Wijas, B.J., Finlayson, G. & Letnic, M. Herbivores’ Impacts Cascade Through the Brown Food Web in a Dryland. Ecosystems (2022). https://doi.org/10.1007/s10021-022-00810-4
- arid land function
- brown food web
- overabundant herbivore