USING COMPILED SPECIES LISTS TO MAKE BIODIVERSITY COMPARISONS AMONG REGIONS - A TEST-CASE USING OREGON BUTTERFLIES

We explore two methods that correct for differential sampling effort w hen estimating the true number of species in a region based on samples such as those typically recorded in museum or conservation databases. The two methods are. (1) a phenomenological model that relies on a sa turating sampling curve; and (2) a model based on a lognormal distribu tion of species abundances. We test these methods using a database for the butterflies of Oregon and find that the distribution of high-dive rsity areas, using the estimated or ''asymptotic'', diversities, is st rikingly different from the geographic pattern one would deduce if the raw data were used, without correcting for differential sampling effo rt. Further, we show that differences in accuracy exist between the tw o estimation procedures, and that these differences are aggravated at small sample sizes; we argue that estimates based on the lognormal dis tribution should be preferred because they can offer substantial impro vement over analyses based solely on the raw data, generally without r isking overestimation. Lastly, using both the database and estimated v alues of butterfly diversity, we show that the distribution of endange red and numerically rare butterflies rarely coincides with ''hotspots' ' or centers of biodiversity. Thus, protecting regions of Oregon rich in overall butterfly diversity will not normally protect the bulk of r are ol endangered butterfly species. (C) 1997 Elsevier Science Ltd.