Abstract:Interspecies competition is the main factor determining the trophic niche width of sympatric species on both ecological and evolutionary levels. In August 2004, a microscopic analysis of feces was made to analyze the diet compositions of Pantholops hodgsoni, Procapra picticaudata and Equus kiang under free-living circumstances between Chuma River and Wudaoliang in the Kekexili National Nature Reserve. The trophic niche widths and overlaps of these herbivorous ungulates were calculated based on the diet compositions, and the results showed that these three ungulates had similar foods, but the proportions of their diet compositions were different. Gramineous plants were the main food sources for P. hodgsoni, P. picticaudata and E. kiang, accounting for 58.7%, 44.57% and 92.28% of the diet, respectively. The trophic niche widths of P. hodgsoni, P. picticaudata and E. kianthese were 0.878, 0.735 and 0.695, and the niche overlaps of P. hodgsoni and E. kiang, P. hodgsoni and P.picticaudata, and E. kiang and P. picticaudata were 0.869, 0.985 and 0.785, respectively, which suggested that there was a potential intense competition among them, especially for P. hodgsoni and P. picticaudata. The relations between competition and coexistence among P. hodgsoni, P. picticaudata and E. kiang were discussed from the viewpoints of their ecological characteristics and trophic ecology.