Simulating randomly selected (unbiased) phenological snapshots from pre-defined populations
For each species, we then generated simulated specimens by: (1) randomly selecting an individual within each population and (2) selecting a random DOY within its individual-level flowering period that emulated the phenological snapshot provided by real herbarium specimens. Specifically, using the distribution of peak flowering dates of each population, we selected an individual at random. From its peak flowering date, we then obtained onset and termination dates by subtracting (for flowering onset) or adding (for flowering termination) half the individual’s flowering duration for that species to the sampled date of peak flowering (Fig. 1b). To simulate a phenological snapshot for that individual, we then randomly selected a DOY between the onset and termination of that individual’s flowering period. As a result, the simulated datum represented a simulated herbarium specimen generated accounting for uncertainty in both the timing of the individual relative to its source population, and in the timing of the collection relative to the onset and termination of that individual’s flowering period. This procedure was repeated across all locations for each simulated species, generating 1000 data points (i.e., simulated specimens or phenological snapshots) per species.