Climate change impacts on population growth across a species’ range differ due to nonlinear responses of populations to climate and variation in rates of climate change

987 in our study) dying after reproducing. Median size of reproducing plans is 3.04 cm3, mini- mum size of reproducing plants is 0.32. To assess D. alaskana’s response to climate change, we conducted a demographic study in populations spanning most of the range [17]. We then regressed vital rates against the climate conditions observed during our study. We used these regressions to construct population-spe- cific climate-driven integral projection models (IPMs). We used projections of future climate from Global Climate Models (GCMs) to predict changes in population growth rate in each population. Finally, we used a decomposition approach to quantify the relative importance of different aspects of climate in eliciting climate change responses. We describe each step in more detail below. To quantify response of D. alaskana to climate, we conducted demographic censuses in five populations (Fig 2) over one annual transition per population. In 2016, we marked and mapped 56 and 196 individuals in 2 populations (C and S in Fig 2), measuring size (sum of basal area x height of all rosettes; S1 Appendix) and number of fruits of each individual. We returned in 2017 to score survival and measure size and number of fruits. In 2017–2018, we Fig 2. Range of Douglasia alaskana and location of study. Map of southcentral Alaska in grey, with the approximate range of D. alaskana indicated by the black polygon [17]. Populations used in this work are indicated by dots, and the labels of populations correspond to those of other figures. The

E2 and E1 populations are offset from one another to allow readability. https://doi.org/10.1371/journal.pone.0247290.g002 PLOS ONE Nonlinear responses of population growth rate to climate change PLOS ONE | https://doi.org/10.1371/journal.pone.0247290 March 3, 2021 4 / 20