1. Department of Zoology, University of Florida, Gainesville, Florida 32611, USA
2. Department of Biology, Washington University, St Louis, Missouri 63130, USA

Correspondence to: Tiffany M. Knight^1,2 Correspondence and requests for materials should be addressed to T.M.K. (Email: tknight@biology2.wustl.edu).

Predation can be intense, creating strong direct and indirect effects throughout food webs^{1, 2, 3, 4}. In addition, ecologists increasingly recognize that fluxes of organisms across ecosystem boundaries can have major consequences for community dynamics^{5, 6}. Species with complex life histories often shift habitats during their life cycles⁷ and provide potent conduits coupling ecosystems^{5, 6}. Thus, local interactions that affect predator abundance in one ecosystem (for example a larval habitat) may have reverberating effects in another (for example an adult habitat). Here we show that fish indirectly facilitate terrestrial plant reproduction through cascading trophic interactions across ecosystem boundaries. Fish reduce larval dragonfly abundances in ponds, leading to fewer adult dragonflies nearby. Adult dragonflies consume insect pollinators and alter their foraging behaviour. As a result, plants near ponds with fish receive more pollinator visits and are less pollen limited than plants near fish-free ponds. Our results confirm that strong species interactions can reverberate across ecosystems, and emphasize the importance of landscape-level processes in driving local species interactions.

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