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Pitcher plant facilitates prey capture in a sympatric congener


Carnivorous plants avoid below-ground competition for nitrogen by utilizing an alternative nitrogen resource—invertebrate prey, but it remains unclear if sympatric carnivorous plants compete for prey resources. The aim of this study was to investigate if exploitative prey-resource competition occurs between the two sympatric pitcher plant species, Nepenthes rafflesiana and N. gracilis in Singapore. We first investigated if prey-resource partitioning occurs between these two species, and then investigated niche shift in N. gracilis by examining its pitcher contents along an in situ gradient of N. rafflesiana interspecific competition. Our results showed clear evidence of resource partitioning between the two species, but contrary to the expectation of competition, proximity to N. rafflesiana pitchers correlated with higher total prey numbers in N. gracilis pitchers. Our multivariate model of prey assemblages further suggested that N. rafflesiana facilitates N. gracilis prey capture, especially in several ant taxa that are trapped by both species. Concurrently, we found strong evidence for intraspecific competition between N. gracilis pitchers, suggesting that prey resources are exhaustible by pitcher-predation. Our results show that resource partitioning can be associated with facilitative interactions, instead of competition as is usually assumed. Facilitation is more typically expected between phylogenetically distant species, but divergences in resource acquisition strategies can permit facilitation between congeners.

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We thank the following individuals for their advice and/or assistance with prey identification: Tan Ming Kai, for the Orthoptera; Ang Yuchen, for the Diptera; John Ascher and Chui Shao Xiong, for the Aculeata; Lee Yueying and Rachel Lim, for the Araneae; Shingo Hosoishi, Seiki Yamane and Eunice Soh, for the Formicidae; Christina Painting and James Koh, for the Opiliones and Anuj Jain and Gan Cheong Weei, for the Lepidoptera. We are grateful also to Stacey Liang and Ester Suen for their assistance in sample collection; and Francis Hui, for technical advice concerning the R package ‘boral’. We thank also Lai Hao Ran and Roman Carrasco for their constructive comments on the manuscript.

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Correspondence to Weng Ngai Lam.

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The authors declare that they have no conflict of interest.

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Communicated by Anna R. Armitage.

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Lam, W.N., Wang, W.Y., Cheong, L.F. et al. Pitcher plant facilitates prey capture in a sympatric congener. Plant Ecol 219, 299–311 (2018).

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  • Nepenthes
  • Resource partitioning
  • Niche shift
  • Niche segregation
  • Facilitation
  • Competition