Faculty of Mathematics and Natural Sciences - Biogeography

Humans matter in food webs

Understanding whether top-down or bottom-up drivers are more important in controlling food webs is a long-standing research question in ecology. Most research to date has focused on assessing this question in natural ecosystems. A new paper published in the Philosophical Transactions of the Royal Society B and led by Ine Dorresteijn shows that in transformed landscapes, humans have an important top-down effect, influencing species across trophic levels. Given that most ecosystems across the global are influenced by land use, the study highlights the need to explicitly embed humans within trophic cascade theory.

Incorporating anthropogenic effects into trophic ecology: predator–prey interactions in a human-dominated landscape


Ine Dorresteijn | Jannik Schultner | Dale G. Nimmo | Joern Fischer |
Jan Hanspach | Tobias Kuemmerle | Laura Kehoe | Euan G. Ritchie

 

Apex predators perform important functions that regulate ecosystems worldwide. However, little is known about how ecosystem regulation by predators is influenced by human activities. In particular, how important are top-down effects of predators relative to direct and indirect human-mediated bottom-up and top-down processes? Combining data on species’ occurrence from camera traps and hunting records, we aimed to quantify the relative effects of topdown and bottom-up processes in shaping predator and prey distributions in a human-dominated landscape in Transylvania, Romania. By global standards this system is diverse, including apex predators (brown bear and wolf), mesopredators (red fox) and large herbivores (roe and red deer). Humans and free-ranging dogs represent additional predators in the system. Using structural equation modelling, we found that apex predators suppress lower trophic levels, especially herbivores. However, direct and indirect topdown effects of humans affected the ecosystem more strongly, influencing species at all trophic levels. Our study highlights the need to explicitly embed humans and their influences within trophic cascade theory. This will greatly expand our understanding of species interactions in human-modified landscapes, which compose the majority of the Earth’s terrestrial surface.

 

Link to the manuscript: DOI:

Citation: Dorresteijn, I., Schultner, J., Ritchie, E. G., Nimmo, D., Hanspach, J., Kuemmerle, T., Kehoe, L., & Fischer, J. (2015): Incorporating human influence into trophic ecology: predator-prey interactions in a human-dominated landscape. Philosophical Transactions of the Royal Society B, in press.