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Estimating species numbers by extrapolation : a cautionary note

Ulrich W.

Polish Journal of Ecology

2001

Vol. 49, nr 3

299-305

This paper evaluates the accuracy any estimator of species may achieve if only a limited fraction (up to 3/4) of the species number in the community has been sampled. From the impossibility to infer the relative abundance distribution (RAD) the rare and not sampled species follow it is shown that it is only possible to give a lower and an upper boundary of the species number. The lower boundary may be inferred either from a fit of a log-normal type RAD or by a graphical method. In the latter case, the lower boundary is S[min]=(ln(d[min]-2icpt) / slope with d[min] being the minimal possible relative density in the community and icpt and slope being the intercept and the slope of the geometric series fitted through the linear part of the log-normal distribution. The upper boundary is found through an extrapolation of this geometric series up to d[min][S[max]=(ln(d[min])-icpt)/slope]. For any estimator to work d[min] has to be known.

The Hymenoptera of a dry meadow on limestone : species composition, abundance and biomass

Ulrich W.

Polish Journal of Ecology

1999

Vol. 47, no 1

29-47

In 1986 and 1988 the hymenopterous fauna of a semixerophytic meadow on limestone near Gottingen (FRG) was studied using ground-photo-eclectors. A total of 4982 speciments belonging to 475 different species were collected. Extrapolations from double-log functions revealed that there may be as many as 1330 parasitoid species present per year. 455 of the 475 species were parasitoids. 155 of them attack dipterans. 48 lepidopterans, 36 beetles, 23 wasps, 22 plant hoppers and 13 aphids, 47 of the species are egg-parasitoids and parasitoids of miners, ectophytophages count for 44 of the wasp species. The abundance of the wasp fauna was rather high (1120+-53 ind. m^-2 a^-1 (1986) and335 +-42 ind. m^-2 a^-1 (1988). Most abundant were the parasitoids of miners, gall-makers and the eggparasitoids. Compared with the high abundance the biomass was low. In 1986 the wasps weighed a total of 194 +-24 mgDW m^-2 a^-1 and in 1988 only 69+-20 mgDW m^-2 a^-1. The parasitoids of ectophytophagous lepidopter ans and coleopterans counted for more than half of the whole biomass.

Estimating species numbers by extrapolation. II, Estimating the adequate sample size

Ulrich W.

Polish Journal of Ecology

1999

Vol. 47, no 3

293-305

On the basis of large model assemblages estimators are developed to predict the sample size necessary to sample a given fraction of the total species number. The classical method that takes the point of leveling off of the species accumulation curves proved to be less efficient than the use of the second order jackknife in determining the sample size necessary to collect exactly half of the species number (N[O.5]). The present paper studies eight newly developed estimators for N[O.5] and shows that estimators based on a Michaelis-Menten formula and a negative exponential model give even better results with minimal sampling effort. The quality of all estimators was not correlated with simple measures of community structure.