The series of a scan need not be species: a scan of getMeanWeight() has a
single series that no model has ever heard of. So the selection is made
against the series the scan actually holds rather than through
valid_species_arg(), which would reject anything that is not a species in
the model.
select_scan_series(available, species)A logical vector selecting the rows to keep.
The Species column of the scan.
The series asked for, as names, as whole-number indices into the series of the scan, or as a logical vector with one entry per series. Must select at least one.