Abstract
Positive species interactions tend to be context dependent. However, it is difficult to predict how benefit in a mutualism changes in response to changing contexts. Nepenthes pitcher plants trap animal prey using leaf pitfall traps known as pitchers. Many specialized inquiline organisms inhibit these pitchers, and are known to facilitate the digestion of prey carcasses in them. Nepenthes gracilis traps diverse arthropod prey taxa, which are likely to differ greatly in the ease with which they may be digested, independently of inquilines, by plant enzymes. In this study, we used in vitro experiments to compare the nutritional benefit provided by phorid (scuttle fly) and culicid (mosquito) dipteran larvae to their host, N. gracilis, and to each other. The effects of phorids on N. gracilis nutrient sequestration were very variable, being positive for large prey which have low digestibility, but negative for small prey which are highly digestible. However, the effect of culicids on N. gracilis and the effects of culicids and phorids on each other were not significantly altered by prey type. These results show that a digestive mutualism is highly dependent on the digestibility of the resource—a context dependency that conforms well to the predictions of the stress–gradient hypothesis in facilitation research. Our findings have significant implications for many other digestive mutualisms, and also suggest that greater insights may be gained from the synthesis of concepts between the fields of mutualism and facilitation research.
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Acknowledgements
We thank Sherry Hung for advice with statistical analysis, as well as Antonia Monteiro and Liew Chye Fong for the provision of various items of laboratory equipment that were essential to the conduct of the study.
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FWSL, WNL, and HTWT composed the study design. FWSL and WNL collected specimens. FWSL conducted the experiments, collected the data, and performed the analysis. WNL wrote the first manuscript draft and all other authors contributed to revisions, approved the final version of the manuscript, and agreed to be held accountable for all aspects of the work presented here
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We intend to deposit data associated with this manuscript in Figshare. Data accessibility Data associated with this article is available at https://doi.org/10.6084/m9.figshare.7064486.v2
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Communicated by Joel Sachs.
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Leong, F.W.S., Lam, W.N. & Tan, H.T.W. A dipteran larva–pitcher plant digestive mutualism is dependent on prey resource digestibility. Oecologia 188, 813–820 (2018). https://doi.org/10.1007/s00442-018-4258-4
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DOI: https://doi.org/10.1007/s00442-018-4258-4