Trophic cascades across ecosystems


Predation can be intense, creating strong direct and indirect effects throughout food webs1,2,3,4. In addition, ecologists increasingly recognize that fluxes of organisms across ecosystem boundaries can have major consequences for community dynamics5,6. Species with complex life histories often shift habitats during their life cycles7 and provide potent conduits coupling ecosystems5,6. 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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Figure 1: Interaction web showing the pathway by which fish facilitate plant reproduction.
Figure 2: Surveyed dragonfly abundances in and near fish-containing and fish-free ponds.
Figure 3: Pollinator visitation rates to Hypericum fasciculatum.
Figure 4: Results from pollen supplementation experiments.
Figure 5: Effects of dragonflies on pollinators.


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We thank T.-L. Ashman, M. Barfield, J. Drake, L. Harmon, J. Knouft, J. Steets, J. M. Chase's lab group and the C. W. Osenberg, B. Bolker and C. St Mary lab group for discussion and comments, T. Kim for field assistance, and S. Coates for logistical support. Funding was provided by The University of Florida Foundation and Washington University in St Louis. Additional support to T.M.K. was through a fellowship from the National Center for Ecological Analysis and Synthesis during the preparation of this manuscript.

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Correspondence to Tiffany M. Knight.

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Supplementary information

Supplementary Methods

Details of additional methods used to determine that there were no environmental or structural differences among pond types and a complementary experiment with another plant show similar trans-ecosystem cascades. (DOC 6735 kb)

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Knight, T., McCoy, M., Chase, J. et al. Trophic cascades across ecosystems. Nature 437, 880–883 (2005).

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