Differences in adult survival drive divergent demographic responses to a decade of field warming on the Tibetan Plateau

O_LIA central question in biodiversity conservation is whether species will maintain viable population dynamics under future climate change. Assessing species extinction risk under climate warming requires demographic studies integrating vital rate responses to long-term warming throughout species life cycle. However, studies of this nature are rare. C_LIO_LIHere, we examine the demographic responses of two co-occurring herbaceous plants, Elymus nutans Griseb. and Helictotrichon tibeticum (Roshev.) Holub, after a decade (2011-2020) of in situ active warming by 2{degrees}C in the grasslands of the Tibetan Plateau. We parameterise Integral Projection Models (IPMs) to project the population dynamics under ambient and long-term warming conditions, and examine the key vital rates responsible for any potential differences in population growth rates. C_LIO_LIWarming has contrasting effects on the two functionally similar co-occurring species: warming promotes the population growth rate of H. tibeticum, but intensifies the population decline of E. nutans. Our elasticity analyses show that survival is the most important vital rate for population viability in both species under both ambient and warmed conditions. Furthermore, our retrospective Life Table Response Experiment (LTRE) analysis reveals that the contrasting fates of the two species under warming mainly arise from the different responses of adult survival, which is significantly promoted in H. tibeticum but slightly reduced in E. nutans. Individual shrinkage occurred 1.6-fold more frequently under warming than ambient conditions for both species, and made considerable negative contributions to their population growth rates in warmed plots. However, such negative effects are offset in H. tibeticum (but not E. nutans) by the positive contribution to population growth rate of the associated increased survival. C_LIO_LISynthesis. Our study illustrates that the responses to climate warming may vary considerably between similar co-occurring species, and species with a demographically compensatory strategy may avoid population collapse. Additionally, caution is needed when generalizing findings among functionally similar species, and that conservation measures should be tailored at the species level. C_LI