Short-term, low-level nitrogen deposition dampens a trophic cascade between bears and plants

Human activities have substantially increased atmospheric nitrogen (N) deposition in ecosystems worldwide, often leading to higher plant quality for herbivores and greater herbivory. Predators frequently suppress herbivores and indirectly benefit plants via ‘trophic cascades’, and the strength of these interactions can also depend on N availability. However, the evidence for N deposition effects on cascades primarily comes from studies of high-level N deposition. Most terrestrial ecosystems currently receive elevated, but low-level N deposition, and it is unclear whether this subtle N enrichment has any effect on cascades. Here, I asked whether low-level N deposition alters a trophic cascade from black bears to plants in Colorado. In this ecological network, bears indirectly benefit plants by consuming ants and suppressing positive effects of ants on herbivores. Using a three year N enrichment experiment, I assessed changes in this cascade by measuring plant and arthropod responses to s...