Nutritional mutualisms of Nepenthes and Roridula

Traps of several carnivorous plant species display characteristics commonly associated with attraction of pollinating insects. These may include a combination of color, scent, and a nectar reward for visitation (Chapter 12). This apparent similarity between carnivorous organs and arthropod-pollinated flowers led some authors to suggest that pitchers were examples of mimicry (e.g., Wiens 1978, Pasteur 1982). Juniper et al. (1989) devoted a chapter to this question, and concluded that convergent evolution of 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 rafflesiana in Borneo. Juniper et al. (1989) developed their argument beyond merely refuting the idea of mimicry. Rather, they hypothesized that some interactions between invertebrates and carnivorous plants possessing 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 nectar reward); 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 Juniper et al. (1989). In this chapter, we review and synthesize the evidence for mutualistic associations between several animal taxa and members of the Nepenthaceae and Roridulaceae that facilitate nutrient acquisition by the plants via their trapping structures