Plant wax alkanes and alcohols as herbivore diet composition markers

The n-alkanes in plant cuticular wax have been used as markers for estimating the species composition of herbivore diets, but the long-chain fatty alcohols (LCOH) of plant wax may also be useful. The objective of this research was to assess if LCOH contributed extra information to differentiate plant species, compared with n-alkanes only. We used 3 data sets consisting of n-alkane and LCOH concentrations of plant species occurring in pastures of New South Wales, Australia. We used Principal Component Analysis (PCA) to summarise the data for n-alkane and LCOH concentrations obtained for the species in these data sets. The first 3 principal components explained 86 to 93% and 75 to 99% of the variance in n-alkane and LCOH concentrations, respectively. Orthogonal Procrustes Rotation (OPR) was then used to compare the results of PCA conducted with n-alkane and LCOH data, with a view to establishing whether LCOH provided discriminatory information in addition to that provided by the n-alkanes. Results of OPR indicated that this was so for all 3 data sets, and suggested that the LCOH would be useful additional markers for discriminating between plant species. We tested this by using Discriminant Analysis and cross-validation procedures in 2 data sets to distinguish between defined species groups of C₃ grasses, C₄ grasses, clovers and Lotus spp. The discrimination between these categories and the proportion of plant species correctly classified into the defined categories was better when using n-alkanes and LCOH together, compared with alkanes alone. Our results indicate that LCOH provided additional information that could be used for distinguishing plant species as part of estimating the species composition of herbivore diets.