To cite funrar in publications use the reference article or the second
reference specifying the package version number

  Matthias Grenié, Pierre Denelle, Caroline M. Tucker, François Munoz,
  Cyrille Violle (2017). “funrar: An R package to characterize
  functional rarity.” _Diversity and Distributions_.
  doi:10.1111/ddi.12629 <https://doi.org/10.1111/ddi.12629>,
  <https://onlinelibrary.wiley.com/doi/10.1111/ddi.12629>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {funrar: {An} {R} package to characterize functional rarity},
    journal = {Diversity and Distributions},
    author = {{Matthias Grenié} and {Pierre Denelle} and {Caroline M. Tucker} and {François Munoz} and {Cyrille Violle}},
    year = {2017},
    url = {https://onlinelibrary.wiley.com/doi/10.1111/ddi.12629},
    doi = {10.1111/ddi.12629},
  }

  Matthias Grenié, Pierre Denelle, Caroline M. Tucker, François Munoz,
  Cyrille Violle (2017). _funrar: An R package to characterize
  functional rarity_. R package version 1.5.0,
  <https://cran.r-project.org/package=funrar>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {funrar: {An} {R} package to characterize functional rarity},
    author = {{Matthias Grenié} and {Pierre Denelle} and {Caroline M. Tucker} and {François Munoz} and {Cyrille Violle}},
    year = {2017},
    note = {R package version 1.5.0},
    url = {https://cran.r-project.org/package=funrar},
  }