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

Abstract

AbstractA 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.Here, we examine the demographic responses of two co-occurring herbaceous plants,Elymus nutansGriseb. andHelictotrichon tibeticum(Roshev.) Holub, after a decade (2011-2020) ofin situactive warming by 2°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.Warming has contrasting effects on the two functionally similar co-occurring species: warming promotes the population growth rate ofH. tibeticum, but intensifies the population decline ofE. 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 inH. tibeticumbut slightly reduced inE. 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 inH. tibeticum(but notE. nutans) by the positive contribution to population growth rate of the associated increased survival.Synthesis. 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.