How do Snow Partridge ( Lerwa lerwa ) and Tibetan Snowcock ( Tetraogallus tibetanus ) coexist in sympatry under high-elevation conditions on the Qinghai-Tibetan Plateau?

The Qinghai-Tibetan Plateau (QTP) has the highest elevations of all biodiversity hotspots. Difficulties involved in fieldwork at high elevations cause challenges in researching mechanisms facilitating species coexistence. Herein, we investigated Snow Partridge ( Lerwa lerwa ) and Tibetan Snowcock ( Tetraogallus tibetanus ), the only two endemic Galliformes on the QTP, to understand species coexistence patterns and determine how they live in sympatry for the first time. We assembled occurrence data, estimated habitat suitability differences and the underlying factors between two species at different scales using ecological niche models. Niche overlap tests were used to investigate whether niche differences between these species allow for their coexistence. We found that elevation was the most important factor determining habitat suitability for both species. At the meso-scale, two species have similar ecological niches with their suitable habitats lying predominantly along ridge crests. However, ridge crests were more influential for habitat suitability by L . lerwa than for that of T . tibetanus because the latter species ranges further afield than ridge crests. Thus, differences in habitat suitability between these species lead to habitat partitioning, which allows stable coexistence. At the macro-scale, temperature and precipitation were major factors influencing habitat suitability differences between these species. Tetraogallus tibetanus extended into the hinterland of the QTP and occurred at higher elevations, where colder and drier alpine conditions are commonplace. Conversely, L . lerwa occurred along the southeastern margin of the QTP with a lower snow line, an area prone to rainy and humid habitats. Niche overlap analysis showed that habitat suitability differences between these species are not driven by niche differentiation. We concluded that the coexistence of these two pheasants under high-elevation conditions could be an adaption to different alpine conditions.