The effects of feeding selectivity on the estimation of diet composition using the n-alkane technique

A limitation to using n-alkanes in plants as faecal markers for estimating diet composition in herbivores is the small number of dietary components that it is possible to determine. One approach to overcoming this is to group species on the basis of their n-alkane concentrations and to consider these groups as dietary components. Feeding selectivity within a group, however, may change the proportion of a particular species in the group ingested and hence its n-alkane contribution to the diet ingested. This could potentially affect estimates of the composition of the diet. Simulations (380) of feeding selectivity within a group of herbage species were undertaken to assess the effects of selectivity on estimates of diet composition. The dataset was from a study whose aim was to estimate the proportions of the herbage component, composed of nineteen species, and of four individual browse species in the diet of red deer grazing a montado ecosystem in S. Portugal in the summer. Simulations were undertaken of total avoidance of each species in the group of herbage species, and selection of each species at 0.5, 1.5, 2.0 and 3.0 of its actual proportion within the group. Feeding selectivity had no effect on 0.36 of the outcomes of the simulations. Over 0.90 of the simulations were within +/-0.05 of the values calculated assuming no selection within the group of herbage species. It is concluded that, in the particular case studied, the effect of selection within a group on the estimates of other dietary components was relatively small and that the group of herbage species could be analysed as a single dietary component.