Using n-alkanes to estimate diet composition of herbivores: a novel mathematical approach

Abstract

N-alkanes are long-chain saturated hydrocarbons occurring in plant cuticles that can be used as chemical markers for estimating the diet composition of herbivores. An important constraint of using n-alkanes to estimate diet composition with currently employed mathematical procedures is that the number of markers must be equal or larger than the number of diet components. This is a considerable limitation when dealing with free-ranging herbivores feeding on complex plant communities. We present a novel approach for the estimation of diet composition using n-alkanes which applies equally to cases where the number of markers is lower, equal or greater than the number of plant species in the diet. The model uses linear programming to estimate the minimum and maximum proportions of each plant in the diet, and avoids the need for grouping species in order to reduce the number of estimated dietary components. We illustrate the model with two data sets of n-alkane content of plants and faeces obtained from a sheep grazing experiment conducted in Australia and a red deer study in Portugal. Our results are consistent with previous studies on those data sets and provide additional information on the proportions of individual species in the diet. Results show that sheep included in the diet high proportions of white clover (from 0.25 to 0.37), and relatively high proportions of grasses (e.g. brome from 0.14 to 0.26) but tended to avoid Lotus spp. (always less than 0.04 of the diet). For red deer we found high proportions of legumes (e.g. Trifolium angustifolium and Vicia sativa reaching maximum proportions of 0.42 and 0.30 of the diet, respectively) with grasses being less important and Cistus ladanifer, a browse, also having relevance (from 0.21 to 0.42 of the diet).

Assessing foraging strategies of herbivores in Mediterranean oak woodlands: a review of key issues and selected methodologies

“…Apart from the different mathematical approaches (Dove 1992;Mayes et al 1994;Dove and Moore 1995;Martins et al 2002a;Barcia et al 2007) which can be used to overcome that limitation, other possible strategies include (i) to combine the discriminatory powers of the n-alkane method with other methods for estimating diet composition; (ii) to decrease the number of plant components to be discriminated by grouping species; (iii) to increase the number of markers in use (Mayes and Dove 2000). For example, microhistology has been used to identify the botanical composition of extrusa from oesophagical fistulated sheep feeding on grassland and shrublands (Salt et al 1994).…”

Evaluation of n-alkanes and their carbon isotope enrichments (δ13C) as diet composition markers

“…A number of mathematical algorithms and approaches including least squares optimisation procedures (Dove and Mayes, 2005) and linear programming (Barcia et al, 2007) have been developed and used for this purpose. Regarding the application of isotopic enrichment, Bugalho et al (2008) demonstrated that the linear programming model of Barcia et al (2007) can be effectively used to estimate the contribution of different sources to a mixture by relating the isotopic composition of carbon (d 13 C) and sulphur (d 34 S) in the sources and mixture. In relation to the present findings, it should also be possible to adopt a suitable mathematical model to use both the n-alkane profiles and their carbon isotopic compositions (d 13 C) as inputs in the calculation of diet compositions.…”

Dietary Selection by Domestic Grazing Ruminants in Temperate Pastures: Current State of Knowledge, Methodologies, and Future Direction

“…In more diverse swards there are usually more plant species available for consumption than there are alkanes to discriminate them. In this case different approaches can be taken: 1) decrease the number of dietary components by grouping species in the diet (e.g., grasses, legumes, and browse) or pooling species with similar n-alkanes profiles for statistical analyses; 2) combining the use of alkanes with other techniques such as microhistological examination of esophageal extrusa (Salt et al 1994) to estimate dietary components; 3) using other mathematical approaches in the use of n-alkanes as markers (Barcia et al 2007); or 4) using additional diet composition markers in plant wax: alkenes (unsaturated aliphatic hydrocarbons), long-chain alcohols (Bughalo et al 2004;Fraser et al 2006), and long chain fatty acids (Ali et al 2004(Ali et al , 2005. These components also have different concentrations in the different plant species and plant parts and can be obtained together with alkanes as part of the same analytical procedure (Dove and Mayes 2006).…”