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How Tibetan red deer ( Cervus elaphus wallichii ) acclimates to high altitude environment during the withered grass period is one of the challenges in maintaining their nutrient intake. It is an important basis to study the nutritional ecology of wild large ungulates in alpine ecosystems by investigating the changes in plant communities with altitude during the withered grass period and how these changes affect the food composition of Tibetan red deer. In this study, we selected the Tibetan red deer in Sangri County, Shannan region of Tibet as the research subject. We carried out field surveys on the altitude, plant communities, and feeding traces of the Tibetan red deer in March of 2021 and 2022 during the withered grass period on the Tibetan Plateau. Detrended correspondence analysis and canonical correspondence analysis were used to study altitudinal variations in plant communities and the regularity of food composition. The results showed that during the period of withered grass, Tibetan red deer ate primarily Salix daltoniana , Rosa macrophylla var. glandulifera and Dasiphora parvifolia . S . daltoniana accounted for more than 50% of the food composition, as the main food resources for red deer in withered grass period. In the low altitude area (4100-4300 m), plant community included Caragana versicolor , R . macrophylla and Berberis temolaica , and Tibetan red deer mainly ate R . macrophylla , C . versicolor and Artemisia wellbyi . In higher altitude area (4300-4600 m), plant community consisted of Rhododendron nivale , Rhododendron fragariiflorum , and Sibiraea angustata , and Tibetan red deer mainly fed on S . daltoniana , Salix obscura , and Carex littledalei . At different altitudes, the dominant plant species were the main food of Tibetan red deer. It is suggested that the changes of plant community composition with altitude directly affected food composition of Tibetan red deer, indicating different food composition patterns with altitude gradients.

Tibetan red deer (Cervus wallichii) is an endemic species to China, which was once considered extinct in the wild. As there are several other wild ungulates and domestic animals with similar feeding habits within its habitat range, it's thus essential to study interspecific competition and co-existence between Tibetan red deer and other cohabiting ungulates in the highly unique environment of Qinghai-Tibet Plateau. Using microscopic analysis on fresh fecal samples collected in Sangri Tibetan Red Deer Nature Reserve from August to September in 2013 and 2014, the trophic niche width and overlap index were calculated on the basis of diet composition of C. wallichii, Cervus albirostris, Procapra picticaudata, Bos mutus and Capra hircas in green grass period. We analyzed and compared the overlap and differentiation of feeding habits between Tibetan red deer and other wild ungulates and domestic animals. The results showed that C. wallichii fed on similar edible plants with other species, but differed in proportion of different dietary components, with the main edible plants of C. wallichii being mostly the secondary edible plants to other species. Leontopodium pusillum was the common main edible plant for C. wallichii (percentage in animal recipes was 11.2%) and B. mutus (10.2%), Salix xizangensis was the common main edible plant of C. wallichii (9.6%) and C. albirostris (11.4%). At plant family level, Leguminosae was the common main edible plant family for C. wallichii (21.4%) and P. picticaudata (42.5%). Cyperaceae was the common main edible plant family for C. albirostris (49.2%), B. mutus (33.4%) and C. hircas (50.3%). Compositae was main edible plant family for C. wallichii (29.6%), as well as the secondary edible plant family for C. albirostris (7.6%), P. picticaudata (11.6%), B. mutus (17.3%) and C. hircas (14.1%). As the secondary edible plant family for C. wallichii (7.1%), Gramineae took up a lower proportion than that of the other ungulates (C. albirostris (13.6%), P. picticaudata (12.3%), B. mutus (11.5%) and C. hircas (16.0%)). Food overlap indices between C. wallichii and the other ungulates were all higher than 0.5, and the highest with B. mutus (0.65). The food diversity index (1.32), evenness index (0.37) and niche width index (15.79) of C. wallichii were all at high values. Compared with the results from 2007 to 2008, dietary composition of Tibetan red deer changed greatly as the proportion of Leguminosae increased while that of Cyperaceae decreased, resulting in improvement of food quality. In addition, there was greater competition of food resources between C. wallichii and domestic animals, which would further affect the distribution range and living space of C. wallichii.