A length axis needs an allometric weight-length relationship for every line
on the plot. The species take theirs from their species parameters and the
resource takes its from resource_params(), where it defaults to the
equivalent spherical diameter (see resource_length_params()). Anything else
— the "Total" row, for instance — has none, and is reported as NA so that
the caller can leave it out.
plot_length_params(species, params)A data frame with columns a and b, one row for each element of
species, holding NA where no relationship is known.
A vector of the species names in the plotting data.
A MizerParams object providing the weight-length parameters.