A comparison of species diversity estimators

Although having been much criticized, diversity indices are still widely us ed in animal and plant ecology to evaluate, survey, and conserve ecosystems . It is possible to quantify biodiversity by using estimators for which sta tistical characteristics and performance are, as yet, poorly defined. In th e present study, four of the most frequently used diversity indices were co mpared: the Shannon index, the Simpson index, the Camargo eveness index, an d the Pielou regularity index. Comparisons were performed by simulating the Zipf-Mandelbrot parametric model and estimating three statistics of these indices, i.e., the relative bias, the coefficient of variation, and the rel ative root-mean-squared error. Analysis of variance was used to determine w hich of the factors contributed most to the observed variation in the four diversity estimators: abundance distribution model or sample size. The resu lts have revealed that the Camargo eveness index tends to demonstrate a hig h bias and a large relative root-mean-squared error whereas the Simpson ind ex is least biased and the Shannon index shows a smaller relative root-mean -squared error, regardless of the abundance distribution model used and eve n when sample size is small. Shannon and Pielou estimators are sensitive to changes in species abundance pattern and present a nonnegligible bias for small sample sizes (<1000 individuals).