Nutritional mutualisms of Nepenthes and Roridula

Traps of several carnivorous plantspecies display characteristics commonly associated with attraction of pollinating insects. These may include a combination of color, scent, and a nectarreward for visitation (Chapter 12). This apparent similarity between carnivorousorgans and arthropod-pollinated flowers led some authors to suggest that pitchers were examples of mimicry(e.g., Wiens 1978, Pasteur 1982). Juniperet al. (1989) devoted a chapter to this question, and concluded that convergent evolutionof attractive traits, rather than mimicry, was responsible for the observed “floral” characteristics of pitcher traps. Moran (1996) reached a similar conclusion based on field studies of Nepenthes rafflesianain Borneo. Juniperet al. (1989) developed their argument beyond merely refuting the idea of mimicry. Rather, they hypothesized that some interactions between invertebrates and carnivorous plantspossessing extrafloral nectaries (EFNs in e.g., Sarracenia, Nepenthes, Cephalotus; Chapter 12) constituted not a predator–prey relationship, but a mutualism: an obligate or facultative interaction between species that is beneficial to both (Boucher et al. 1982). Within this broad definition, many mutualistic associations have been identified, including: resource/service (e.g., pollination of flowers by an animal for a nectarreward); service/service (e.g., ants protecting a host plant from herbivory in exchange for nesting space); and resource/resource or resource exchange (e.g., association between mycorrhizal fungi and green plants).Subsequent studies have provided support for the mutualistic hypothesis of Juniperet al. (1989). In this chapter, we review and synthesize the evidence for mutualistic associations between several animal taxa and members of the Nepenthaceae and Roridulaceaethat facilitate nutrient acquisition by the plants via their trapping structures.