Extrafloral nectaries mediate the arboreal beetle community (Coleoptera) in a Neotropical rainforest

ABSTRACT

Nectaries are structures that secrete a sugary solution and can occur on vegetative and/or reproductive parts of plants. The significance of floral nectaries to reward vertebrate and arthropod pollinators is well supported. The role of extrafloral nectaries (EFNs) is more ambiguous, though research has been skewed to the ant-plant mutualism. Many other insects feed at EFNs, but these interactions are vastly understudied. This study addresses the hypothesis that EFNs may influence the occurrence and structure of Neotropical canopy beetle communities. Seven canopy trees (four families) exhibiting EFNs and their associated beetles were studied over a one-year period in southern Venezuela. In total, 6818 adult beetles identified to 868 species were recorded on 25 investigated canopy tree species (#47 individuals). Of the 868 beetle species, 150 species (517 individuals; 17.3% species) from 20 families were observed drinking from foliar EFNs on seven EFN-bearing tree species. Dietary dependence on EF nectar varied, with 95 beetle species utilising this nectar within a broader diet and 55 species found feeding exclusively on EFNs. This study demonstrates unequivocally that EF nectar is a frequently utilised food resource of many beetle adults and beetles have been a significantly underestimated visitor group. A more detailed study was conducted on six individual canopy trees of two species of Chrysobalanaceae, Licania hebantha Mart. ex Hook. f. and Moquilea subarachnophylla (Cuatrec.) Sothers and Prance. In total, 115 individual adults of 64 beetle species were collected on nectar secreted on newly-sprouted leaves. These beetle assemblages were dominated by species utilising EF nectar and were associated with distinct phenological phases of the host trees. Altogether, the beetle survey found support for the hypothesis that EFNs influence the occurrence and structure of beetle communities. These beetle-EFN relationships have implications for spatial arrangement, community assembly and evolution of both host plants and beetles. Like ant-EFN mutualism, EFN-bearing trees and beetles may also form mutualism. It is possible that the plants offer easier access to a nutritious resource that may deflect herbivory of vegetative parts.

KEYWORDS:

• Amazonia
• biodiversity
• canopy
• crane
• nectarivory
• plant-insect interactions

Acknowledgements

We thank cordially taxonomic experts named under Material and Methods for identifying beetles. We are grateful to Jens Wesenberg for superior assistance in all botanical matters. Brigitte Marazzi and Cynthia A. Sothers supported our manuscript with discussing the identifications of some tree species. Brigitte Marazzi generously provided Figure 1(b). We thank Martin Heil, Margarete de Macedo, Brigitte Marazzi and Maximilian Weigend for their valuable comments on the manuscript. The Austrian Academy of Sciences and colleagues are gratefully acknowledged for their support and permission to join the Surumoni project. The fieldwork of SK was supported, in part, by a travel grant from the ESF Tropical Canopy Programme and a grant from the Stiftung der Deutschen Wirtschaft.

Disclosure statement

No potential conflict of interest was reported by the authors.

Geolocation information

The study site is located in the upper Orinoco region state of Amazonas, Venezuela: 3°10ʹN, 65°40ʹW.

Additional information

Funding

This work was supported by the ESF Tropical Canopy Programme [travel grant]; and the Stiftung der Deutschen Wirtschaft [3-year fulltime scholarship]; European Science Foundation [Tropical Canopy Programme].