Population dynamics
We selected the four populations in Pujin pasture (Figure S1) to identify the current and historical distribution patterns of individual cushions in their communities, by taking a landscape conception and approach (Pickett & Cadenasso, 1995). See Text S4 for the details.
To characterize the current population structures, we determined the age structure and density of each population. Since it is impossible to determine the real age of this slowly-growing cushion species, we used the size of individuals as a proxy for age (Molau, 1997; Benedict, 1989; Chen et al., 2020a). See Text S5 for the details.
To characterize population productivity, each population’s flower production was assessed in early July 2021, when A. polytrichoides plants were blooming. The flowering ratio (i.e. , flowering area/total cushion surface area) of each individual was assessed and recorded. The same process was applied to determine fruit production in late September when fruits had matured. The fruits are very small (ca. 3-4 mm) and each contains nearly three seeds on average (2.87 ± 0.14, mean ± s.e.), so rather than laboriously collecting and dissecting fruits we simply used fruit production as a proxy of population production in this study. We initially followed a previously published protocol (Zhang et al., 2020) to assess the flowering/fruiting ratio of 50 randomly chosen individuals in each population, then by experience visually assessed the reproductive production of the remaining individuals due to time constraints. See Text S6 for the details.