Species richness in an assemblage is frequently used as a measure of biological diversity. However, observed species richness is strongly dependent on sample size. If more samples are collected, then more species are observed. Non-parametric species richness estimators, such as the jackknife 1 and 2 and the Chao 1 and 2, are indicated in the literature as potential solutions to the problem of dependence of observed species richness on sampling effort. These methods are intended to estimate the total species richness in an area or assemblage with small sampling effort. Non-parametric estimators are based on the number of species observed, and the number of rare species in a sample, i.e., that occurred in one and/or two sampling units, or with one and/or two individuals. High estimates are produced when samples contain large proportions of rare species. Using a range of real datasets, I show that estimates produced by non-parametric methods are generally dependent on observed species richness. An implicit assumption of these non-parametric techniques is that the rare species curve should present high values at small sample sizes and decreasing values as sampling effort is increased. This assumption was observed in only one out of eight datasets presented. Instead, the rare species curve generally flattens off around a constant value as sampling effort increases. I conclude that non-parametric estimators are not reliable to estimate species richness in an assemblage when the rare species curve does not show a decreasing trend. Comments are made on the possibilities of using non-parametric estimators in the comparison of species assemblages.
Brown, K.S.Jr. and A.V.L. Freitas. 2000. Atlantic forest butterflies: indicators for landscape conservation. Biotropica 32:934-956.
'Atlantic forest butterflies: indicators for landscape conservation ' () 32 Biotropica : 934 -956 .
Burnham, K.P. and W.S. Overton. 1978. Estimation of the size of a closed population when capture probabilities vary among animals. Biometrika 65:625-633.
'Estimation of the size of a closed population when capture probabilities vary among animals ' () 65 Biometrika : 625 -633 .
Bini, L.M., S.M. Thomaz and D.C. Souza. 2001. Species richness and β-diversity of aquatic macrophytes in the Upper Paraná River floodplain. Arch Hydrobiol. 151:511-525.
'Species richness and β-diversity of aquatic macrophytes in the Upper Paraná River floodplain ' () 151 Arch Hydrobiol : 511 -525 .
Butler, B.J. and R.L. Chazdon. 1998. Species richness, spatial variation, and abundance of the soil seed bank of a secondary tropical rain forest. Biotropica 30:214-222.
'Species richness, spatial variation, and abundance of the soil seed bank of a secondary tropical rain forest ' () 30 Biotropica : 214 -222 .
Chao, A. 1984. Nonparametric estimation of the number of classes in a population.Scand. J. Stat. 11:265-270.
'Nonparametric estimation of the number of classes in a population ' () 11 Scand. J. Stat : 265 -270 .
Chao, A. 1987. Estimating the population size for capture-recapture data with unequal catchability. Biometrics 43:783-791.
'Estimating the population size for capture-recapture data with unequal catchability ' () 43 Biometrics : 783 -791 .
Chazdon, R.L., R.K. Colwell, J.S. Denslow and M.R. Guariguata. 1998. Statistical methods for estimating species richness of woody regeneration in primary and secondary rain forest of northeastern Costa Rica. In: F. Dallmeier and J. A. Comiskey (eds.), Forest Biodiversity Research, Monitoring and Modeling: Conceptual Background and Old World Case Studies. Parthenon Publishing, Paris, pp. 285-309.
Statistical methods for estimating species richness of woody regeneration in primary and secondary rain forest of northeastern Costa Rica. , () 285 -309 .
Chiarucci, A., N.J. Enright, G.L.W. Perry, B.P. Miller and B.B. Lamont. 2003. Performance of nonparametric species richness estimators in a high diversity plant community. Div. Distrib. 9: 283-295.
'Performance of nonparametric species richness estimators in a high diversity plant community ' () Div. Distrib. : 283 -295 .
Longino, J.T., J. Coddington and R.K. Colwell. 2002. The ant fauna of a tropical rain forest: estimating species richness three different ways. Ecology 83:689-702.
'The ant fauna of a tropical rain forest: estimating species richness three different ways ' () 83 Ecology : 689 -702 .
Magurran, A.E. 1988. Ecological Diversity and its Measurement. Croom Helm, London.
Ecological Diversity and its Measurement , ().
Magurran, A.E. and P.A. Henderson. 2003. Explaining the excess of rare species in natural species abundance distributions. Nature 422:714-716.
'Explaining the excess of rare species in natural species abundance distributions ' () 422 Nature : 714 -716 .
Coddington, J.A., C.E. Griswold, D.S. Dávila, E. Peńaranda and S.F. Larcher. 1991. Designing and testing sampling protocols to estimate biodiversity in tropical ecosystems. In: E. C. Dudley (ed.), The Unity of Evolutionary Biology: Proceedings of the Fourth International Congress of Systematics and Evolutionary Biology. Dioscorides Press, Portland, pp. 44-60.
Designing and testing sampling protocols to estimate biodiversity in tropical ecosystems. , () 44 -60 .
Colwell, R. K. 1997. Estimates: Statistical estimation of species richness and shared species from samples. Version 5. User's Guide and application published at: http://viceroy.eeb. uconn.edu/estimates
Estimates: Statistical estimation of species richness and shared species from samples. Version 5. , ().
Colwell, R.K. and J.A. Coddington. 1994. Estimating terrestrial biodiversity through extrapolation. Philos. Trans. R. Soc. Land. B 345:101-118.
'Estimating terrestrial biodiversity through extrapolation ' () 345 Philos. Trans. R. Soc. Land. B : 101 -118 .
Condit, R., S.P. Hubbell, J.V. Lafrankie, R. Sukumar, N. Manokaran, R.B. Foster and P.S. Ashton. 1996. Species-area and species-individual relationships for tropical trees: a comparison of three 50-ha plots. J. Ecol. 84:549-562.
'Species-area and species-individual relationships for tropical trees: a comparison of three 50-ha plots ' () 84 J. Ecol. : 549 -562 .
Fisher, R.A., A.S. Corbet and C.B. Williams. 1943. The relation between the number of species and the number of individuals in a random sample of an animal population. J. Anim. Ecol. 12:42-58.
'The relation between the number of species and the number of individuals in a random sample of an animal population ' () 12 J. Anim. Ecol. : 42 -58 .
Fisher, B.L. 1999a. Ant diversity patterns along an elevational gradient in the Réserve Naturelle Integrate d'Andohahela, Madagascar. Fieldiana Zoology (n.s.) 94:129-147.
'Ant diversity patterns along an elevational gradient in the Réserve Naturelle Integrate d'Andohahela, Madagascar ' () 94 Fieldiana Zoology : 129 -147 .
Fisher, B.L. 1999b. Improving inventory efficiency: a case study of leaf-litter ant diversity in Madagascar. Ecol. Appl. 9:714-731.
'Improving inventory efficiency: a case study of leaf-litter ant diversity in Madagascar ' () Ecol. Appl : 714 -731 .
Gotelli, N.J. and R.K. Colwell. 2001. Quantifying biodiversity: procedures and pitfalls in the measurement and comparison of species richness. Ecol. Lett. 4:379-391.
'Quantifying biodiversity: procedures and pitfalls in the measurement and comparison of species richness ' () Ecol. Lett : 379 -391 .
Grassle, J.F. and N.J. Maciolek. 1992. Deep-sea species richness: regional and local diversity estimates from quantitative bottom samples. Am. Nat. 139:313-341.
'Deep-sea species richness: regional and local diversity estimates from quantitative bottom samples ' () 139 Am. Nat. : 313 -341 .
Hellmann, J.J. and G.W. Fowler. 1999. Bias, precision, and accuracy of four measures of species richness. Ecol. Appl. 9:824-834.
'Bias, precision, and accuracy of four measures of species richness ' () Ecol. Appl : 824 -834 .
Keating, K.A. and J.F. Quinn. 1998. Estimating species richness: the Michaelis-Menten model revisited. Oikos 81:411-416.
'Estimating species richness: the Michaelis-Menten model revisited ' () Oikos : 411 -416 .
Melo, A.S., R.A.S. Pereira, A.J. Santos, G J. Shepherd, G. Machado, H.F. Medeiros and RJ. Sawaya. 2003. Comparing species richness among assemblages using sample units: why not use extrapolation methods to standardize different sample sizes? Oikos 101:398-410.
'Comparing species richness among assemblages using sample units: why not use extrapolation methods to standardize different sample sizes ' () 101 Oikos : 398 -410 .
Oliver, I. and A.J. Beattie. 1996. Invertebrates morphospecies as surrogates for species: a case study. Conserv. Biol. 10:99-109.
'Invertebrates morphospecies as surrogates for species: a case study ' () 10 Conserv. Biol : 99 -109 .
Palmer, M.W. 1990. The estimation of species richness by extrapolation. Ecology 71:1195-1198.
'The estimation of species richness by extrapolation ' () 71 Ecology : 1195 -1198 .
Patil, G.P. and C. Taillie. 2001. Estimation of species richness based on species range. Community Ecol. 2:209-211.
'Estimation of species richness based on species range ' () Community Ecol. : 209 -211 .
Southwood, T.R.E. 1978. Ecological Methods. Chapman and Hall, New York.
Ecological Methods. , ().
Stout, J. and J. Vandermeer. 1975. Comparison of species richness for stream-inhabiting insects in tropical and mid-latitude streams. Am. Nat. 109:263-280.
'Comparison of species richness for stream-inhabiting insects in tropical and mid-latitude streams ' () 109 Am. Nat. : 263 -280 .
Taylor, L.R., R.A. Kempton and I.P. Woiwod. 1976. Diversity statistics and the Log-Series model. J. Anim. Ecol. 45:255-272.
'Diversity statistics and the Log-Series model ' () 45 J. Anim. Ecol. : 255 -272 .
Toti, D.S., F.A. Coyle and J.A. Miller. 2000. A structured inventory of Appalachian grass bald and heath bald spider assemblages and a test species richness estimator performance. J. Arachnol. 28:329-345.
'A structured inventory of Appalachian grass bald and heath bald spider assemblages and a test species richness estimator performance ' () 28 J. Arachnol : 329 -345 .
Wagner, H.H. and O. Wildi. 2002. Realistic simulation of the effects of abundance distribution and spatial heterogeneity on non-parametric estimators of species richness. Ecoscience 9:241-250.
'Realistic simulation of the effects of abundance distribution and spatial heterogeneity on non-parametric estimators of species richness ' () Ecoscience : 241 -250 .
Walther, B.A. and J.-L. Martin. 2001. Species richness estimation of bird communities: how to control for sampling effort? Ibis 143:413-419.
'Species richness estimation of bird communities: how to control for sampling effort ' () 143 Ibis : 413 -419 .
Melo, A.S. and C.G. Froehlich. 2001a. Evaluation of methods for estimating macroinvertebrates species richness using individual stones in tropical streams. Freshwater Biol. 46:711-721.
'Evaluation of methods for estimating macroinvertebrates species richness using individual stones in tropical streams ' () 46 Freshwater Biol : 711 -721 .
Melo, A.S. and C.G. Froehlich. 2001b. Macroinvertebrates in neotropical streams: richness patterns along a catchment and assemblage structure between 2 seasons. J. North Am. Benthol. Soc. 20:1-16.
'Macroinvertebrates in neotropical streams: richness patterns along a catchment and assemblage structure between 2 seasons ' () 20 J. North Am. Benthol. Soc. .
Minshall, G.W., R.C.J. Petersen and C.F. Nimz. 1985. Species richness in streams of different size from the same drainage basin. Am. Nat. 125:16-38.
'Species richness in streams of different size from the same drainage basin ' () 125 Am. Nat. : 16 -38 .
Novotný, V. and Y. Basset. 2000. Rare species in communities of tropical insect herbivores: pondering the mystery of singletons. Oikos 89:564-572.
'Rare species in communities of tropical insect herbivores: pondering the mystery of singletons ' () 89 Oikos : 564 -572 .