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Birds help plants: a meta-analysis of top-down trophic cascades caused by avian predators

Abstract

The tritrophic interactions between plants, herbivores and avian predators are complex and prone to trophic cascades. We conducted a meta-analysis of original articles that have studied birds as predators of invertebrate herbivores, to compare top-down trophic cascades with different plant responses from different environments and climatic areas. Our search found 29 suitable articles, with a total of 81 separate experimental study set-ups. The meta-analysis revealed that plants benefited from the presence of birds. A significant reduction was observed in the level of leaf damage and plant mortality. The presence of birds also positively affected the amount of plant biomass, whereas effects on plant growth were negligible. There were no differences in the effects between agricultural and natural environments. Similarly, plants performed better in all climatic areas (tropical, temperate and boreal) when birds were present. Moreover, both mature plants and saplings gained benefits from the presence of birds. Our results show that birds cause top-down trophic cascades and thus they play an integral role in ecosystems.

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Acknowledgements

We would like to thank Pälvi Salo for help and advice. Thanks are also due to Christiaan Both, Leena Lindström, Lauri Oksanen, Cagan Sekercioglu, three anonymous reviewers and the graduate student seminar at the section of ecology (University of Turku), for giving valuable comments. Kevin O’Brien checked the English. The study was financially supported by the Jenny and Antti Wihuri Foundation (grant to E.M.), Academy of Finland (decision numbers 111195 and 129143 to T.K.) and the Emil Aaltonen Foundation (grant to T.L.).

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Correspondence to Elina Mäntylä.

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Communicated by Chris Whelan.

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Electronic Supplemental Material 1

A normal quantile plot with 95 % confidence interval lines for examining publication bias of the studies used in the overall effect meta-analysis (N = 44) (JPEG 6221 kb)

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A funnel plot showing the relationship between the effect size (lnR) and sample size of the original studies (N = 44). N is the combined sample size of treatment and control plots. The two outliers are the two studies of algae as plants (Wootton 1992, 1995) (JPEG 434 kb)

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Mäntylä, E., Klemola, T. & Laaksonen, T. Birds help plants: a meta-analysis of top-down trophic cascades caused by avian predators. Oecologia 165, 143–151 (2011). https://doi.org/10.1007/s00442-010-1774-2

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Keywords

  • Herbivory
  • Indirect effects
  • Meta-analysis
  • Predation
  • Trophic interactions