Simulation check and uncertainty in introduction and
naturalisation dates
I used simulation to check the methods described above worked as
expected, using known parameter values to generate artificial data
similar to the real data, fitting the lag time model to the artificial
data and estimating the invasion debt, and assessing how well the
methods recovered the true parameter values using repeated simulations.
Full details are in Appendix S4.
The dates of first introduction and naturalisation in this study are
taken from historical records and are subject to uncertainty, notably
because the true dates might not have been documented or the records
have not been uncovered, resulting in first record dates being more
recent than true dates. While dates can be updated as new records are
discovered, any set of dates will be subject to uncertainty due to the
difficulty of determining precisely when past events occurred. The
question is whether this uncertainty could affect the results reported
in this study. To evaluate this, I used artificial data simulation as
described above but added measurement error to the simulated dates. I
then assessed how well the methods recovered the true parameter values
in the presence of dating errors using repeated simulations. Full
details are in Appendix S5.