Termite Prey Specialization in the Pitcher Plant Nepenthes albomarginata—Evidence from Stable Isotope Analysis

Old World pitcher plants (Nepenthes spp., Nepenthaceae) trap and digest invertebrate prey to derive nutrients, primarily nitrogen (N). In the majority of lowland Nepenthes species studied to date, ants (Hymenoptera, Formicidae) are numerically the dominant prey taxon. Nepenthes albomarginata is unusual in showing an apparent bias towards the capture of termites (Isoptera). We tested the hypothesis that N. albomarginata derives N from termite capture, by comparison of foliar stable N isotope abundance (δ15N) with a sympatric species (N. rafflesiana), whose verified major prey group is ants. N. albomarginata showed significantly lower δ15N values than N. rafflesiana, reflecting the lower δ15N value of termite tissue relative to that of ants, and suggesting a degree of prey segregation between the two Nepenthes species. Using mixing models, we estimated that termites (Hospitalitermes sp.) contribute 53.8±7.3% of the total foliar N in N. albomarginata, and that ants (Crematogaster sp.) contribute 68.1±2.4% of the total foliar N in N. rafflesiana. We also investigated the carbon stable isotope abundance (δ13C) in both species.N. albomarginata showed higher δ13C values and a lower estimated intercellular partial pressure of CO2(Ci) than N. rafflesiana, indicating either higher water use efficiency (due to water stress) or greater photosynthetic capacity.