Altitudinal gradients of grassland carbon and nitrogen isotope composition are recorded in the hair of grazers

• Published in: Global ecology and biogeography 2007-09, Vol.16 (5), p.583-592
• Main Authors: Männel, Tobias Tassilo, Auerswald, Karl, Schnyder, Hans
• Format: Article
• Language: English
• Subjects: Alps; Altitude; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Biological and medical sciences; Bos taurus; Capra hircus; cattle; Diet; Fundamental and applied biological sciences. Psychology; General aspects; General aspects. Techniques; Generalities; Goats; Grasses; Hair; isotope ecology; Isotopes; Ovis aries; Pastures; Ruminantia; Sheep; stable isotopes; Synecology; trophic shift; Vegetation; δ13C; δ15N
• ISSN: 1466-822X; 1466-8238; 1466-822X
• DOI: 10.1111/j.1466-8238.2007.00322.x

The hair of grazers provides an isotopic record of environmental and nutritional signals. Here, we assess the effect of altitude on the carbon and nitrogen isotope composition of the hair of ruminant grazers and its relation to grassland vegetation, to evaluate the use of hair isotope data for ecosystem reconstruction, animal nutritional ecology and biogeochemical studies in montane environments. European Alps. We sampled grassland vegetation (pure C₃) and the hair of ruminants along an altitudinal gradient (400-2500 m), and analysed their isotope composition (δ¹³C and δ¹⁵N). Results were compared with published effects of altitude on ¹³C in C₃ plants at the species level and on ¹⁵N at the community level. The study was complemented with a comparison of diet and hair isotope composition in ruminants held in confinement. δ¹³C of hair increased (c. 1.1[per thousand] km⁻¹) and δ¹⁵N decreased (c. 1.1[per thousand] km⁻¹) with altitude. The same changes occurred in local grassland vegetation, and in regional to global grassland data sets. Offsets between hair and vegetation ¹³C or ¹⁵N ('diet-hair shift') were independent of altitude. Sheep (Ovis aries) and cattle (Bos taurus) exhibited a ¹³C shift near +3[per thousand], but that of goats (Capra hircus) was larger (+4.2[per thousand]) in alpine environments and in confinement. The diet-hair shift for ¹⁵N was more variable (+2.1 to +3.6[per thousand]). Grazer hair provides a faithful spatially and temporally integrated record of grassland isotope composition, useful for ecosystem and environment reconstruction. The effect of altitude on hair ¹⁵N is important for studies of trophic relationships: an altitude shift of 2000 m produced the same effect in hair ¹⁵N as would a shift from an animal tissue-based to a plant-based diet. The similarity of altitude effects on δ¹³C of individual plant species, vegetation and hair indicates that the effect of altitude on species-level 'intrinsic water use efficiency' scales up linearly to the community and landscape level.