Figure Legends
Figure 1 . Sampling of Phyllotis vaccarum across an elevational gradient in the Altiplano and Puna de Atacama of northern Chile, Regiόn de Antofagasta. (a) Map of seven collection localities on the flanks of Volcán Lullaillaco and the surrounding Altiplano. (b) Elevational profile of sampling transect, with sampling localities 1 to 7 shown in ascending order of elevation, from 2370 m (site 1) to 6739 m (the summit of Volcán Lullaillaco, site 7). (c) Northwest face of Volcán Llullaillaco (24°43.21′S, 68°32.22′W). Photo was taken from a point several km northwest of the site 3 on the transect. Photo: J.F. Storz.
Figure 2 . Schematic figure of the dissected portions of the gastrointestinal tract of the mouse from the summit of Volcán Llullaillaco. Contents of the upper digestive tract (stomach) were analyzed via metagenomics and DNA metabarcoding. Contents of the lower digestive tract (separated into the cecum and 12 consecutive segments from the outlet of the cecum to the rectum) were analyzed via DNA metabarcoding.
Figure 3 . Taxonomic composition of reads identified through metabarcoding for the stomach, cecum and 12 consecutive portions of the lower GI from the outlet of the cecum to the rectum. (A) Proportion of sequence reads per taxon for the marker trn and (B) proportion of total reads for the same marker with Erythroxylaceae excluded. (C) Proportion of sequence reads per taxon for the marker ITS2 and (D) proportion of total reads for the same marker with Erythroxylaceae excluded. (E) Proportion of sequence reads per taxon for the marker23S   and (F) proportion of total reads for the same marker with Erythroxylaceae excluded.
Figure 4 . Taxonomic composition of Ascomycota (A) and Basidiomycota (B) at the Order and Family levels.
Figure 5. Variation in stable isotopes in livers of Phyllotis vaccarum sampled from different elevational zones: (A) δ13C, (B) δ15N, and (C) δ34S. (D) Results of multivariate CAP ordination based on Euclidean distances calculated from combined δ13C, δ15N and δ34S values.
Figure 6. Variation in plant δ13C (A) and δ15N (B) across different elevational zones. Values taken from Díaz et al. (2016). Note the elevational shift in δ13C values showing dominance of C4plants at lower elevations, a mix of C3, C4 and CAM plants at mid-elevations and a shift to C3 plants at higher elevations. Plant δ15N values were similar at lower and mid-elevations but were relatively 15N depleted at higher elevations. These data were used to define isotopic baselines for estimates of trophic position of P . vaccarum .