Termite prey specialization in the pitcher plant Nepenthes albomarginata -Evidence from stable isotope analysis

Old World pitcher plants (Nepenthes spp., Nepenthaceae) trap and digest inv ertebrate prey to derive nutrients, primarily nitrogen (N). In the majority of lowland Nepenthes species studied to date, ants (Hymenoptera, Formicida e) are numerically the dominant prey taxon. Nepenthes albomarginata is unus ual in showing an apparent bias towards the capture of termites (Isoptera). We tested the hypothesis that N. albomarginata derives N from termite capt ure, by comparison of foliar stable N isotope abundance (delta N-15) with a sympatric species (N. rafflesiana), whose verified major prey group is ant s. N. albomarginata showed significantly lower delta N-15 values than N. ra fflesiana, reflecting the lower delta N-15 value of termite tissue relative to that of ants, and suggesting a degree of prey segregation between the t wo Nepenthes species. Using mixing models, we estimated that termites (Hosp italitermes sp.) contribute 53.8 +/- 7.3 % of the total foliar N in A. albo marginata, and that ants (Crematogaster sp.) contribute 68.1 +/- 2.4 % of t he total foliar N in N. rafflesiana. We also investigated the carbon stable isotope abundance (delta C-13) in both species. N. albomarginata showed hi gher delta C-13 values and a lower estimated intercellular partial pressure of CO2 (C-i) than N. rafflesiana, indicating either higher water use effic iency (due to water stress) or greater photosynthetic capacity. (C) 2001 An nals of Botany Company.