To cite SPECIES in publications use:

Wang J (2011). “SPECIES: An R Package for Species Richness Estimation.” Journal of Statistical Software, 40(9), 1–15. https://www.jstatsoft.org/index.php/jss/article/view/v040i09.

Corresponding BibTeX entry:

  @Article{,
    title = {{SPECIES}: An {R} Package for Species Richness
      Estimation},
    author = {Ji-Ping Wang},
    journal = {Journal of Statistical Software},
    year = {2011},
    volume = {40},
    number = {9},
    pages = {1--15},
    url =
      {https://www.jstatsoft.org/index.php/jss/article/view/v040i09},
  }