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.