Habitat modification alters the structure of tropical host–parasitoid food webs (original) (raw)

Nature volume 445, pages 202–205 (2007) Cite this article

Abstract

Global conversion of natural habitats to agriculture has led to marked changes in species diversity and composition1. However, it is less clear how habitat modification affects interactions among species2. Networks of feeding interactions (food webs) describe the underlying structure of ecological communities, and might be crucially linked to their stability and function3,4,5,6,7. Here, we analyse 48 quantitative food webs8,9 for cavity-nesting bees, wasps and their parasitoids across five tropical habitat types. We found marked changes in food-web structure10,11 across the modification gradient, despite little variation in species richness. The evenness of interaction frequencies declined with habitat modification, with most energy flowing along one or a few pathways in intensively managed agricultural habitats. In modified habitats there was a higher ratio of parasitoid to host species and increased parasitism rates, with implications for the important ecosystem services, such as pollination and biological control, that are performed by host bees and wasps12. The most abundant parasitoid species was more specialized in modified habitats, with reduced attack rates on alternative hosts. Conventional community descriptors failed to discriminate adequately among habitats, indicating that perturbation of the structure and function of ecological communities might be overlooked in studies that do not document and quantify species interactions. Altered interaction structure therefore represents an insidious and functionally important hidden effect of habitat modification by humans.

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Figure 1: Quantitative host–parasitoid food webs along a gradient of increasing habitat modification (top to bottom).

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Figure 2: The effects of habitat modification on rates of parasitism (mean ± s.e.m.) and six quantitative food web metrics (see Supplementary Methods 1): linkage density (LD), generality, vulnerability, evenness, connectance and compartment diversity.

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Acknowledgements

We thank J. Bascompte, M. B. Bonsall, M. M. Bos, H. C. J. Godfray, B. A. Hawkins, R. J. Morris, C. B. Müller and T. Roslin for discussions or comments, and J. Casquete, J. Pico, G. Sacoto, C. Valarezo, C. Calderon, A. Choez, J. Lino, R. Olschewski, G. H. J. de Koning and B. Pico for assistance with field or laboratory work and coordination. H. C. J. Godfray provided software and advice for drawing food webs and calculating compartmentalization. This research was funded by the Federal Ministry for Research and Education (BMBF) Germany, and a Royal Society University Research Fellowship to O.T.L.

Author Contributions J.M.T. was responsible for writing, field data collection, research planning and analysis; T.T. for research planning, site selection and funding application; and O.T.L. for writing, analysis and preparation of food webs (Fig. 1). All authors discussed the results and edited the manuscript.

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  1. Jason M. Tylianakis
    Present address: School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, 8020, New Zealand

Authors and Affiliations

  1. Agroecology, Georg August University, Waldweg 26, Goettingen, D-37073, Germany
    Jason M. Tylianakis & Teja Tscharntke
  2. Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK
    Owen T. Lewis

Authors

  1. Jason M. Tylianakis
  2. Teja Tscharntke
  3. Owen T. Lewis

Corresponding author

Correspondence toJason M. Tylianakis.

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Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests.

Supplementary information

Supplementary Information (download PDF )

This file contains Supplementary Methods 1-3 detailing calculation of food web statistics, and analyses of evenness and parasitism; Supplementary Figure 1 showing qualitative food web values across habitats; and Supplementary Tables 1-4 presenting results of supporting analyses and details of host and parasitoid codes used in Fig. 1. (PDF 563 kb)

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Tylianakis, J., Tscharntke, T. & Lewis, O. Habitat modification alters the structure of tropical host–parasitoid food webs.Nature 445, 202–205 (2007). https://doi.org/10.1038/nature05429

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Editorial Summary

A tangled web

Global change has the potential to influence species interactions, but the consequences for ecosystem function and stability are hard to predict. Quantitative food webs provide a powerful tool to probe such questions, but to date they have been used mainly to describe individual communities. A study of 48 plots in the Choco-Manabi region of Ecuador, where large-scale agriculture threatens biodiversity, now confirms that human habitat modification can dramatically affect networks of feeding interactions among species in host–parasitoid food webs. The switch from tropical rainforest to intensive agriculture has negative consequences for bees and wasps, which are important for pollination and biological pest control.