To cite SPECIES in publications use:

Ji-Ping Wang (2011). SPECIES: An R Package for Species Richness Estimation. Journal of Statistical Software, 40(9), 1-15. URL http://www.jstatsoft.org/v40/i09/.

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 = {http://www.jstatsoft.org/v40/i09/},
  }