. Bonn zoological bulletin. Zoology. Estimating herpetofaunal species richness 5. Fig. 2. A: Heosemys spinosa (Gray, 1831); B: Kaloula pulchra Gray, 1831; C: Naja sumatrana (Mtiller, 1890); D: Tropidolae- mus wagleri (Boie, 1827). 2005). Four models were fitted to the rarefaction curve. The first corresponds with a negative exponential model (Colwell & Coddington 1994; Flather 1996; Van Rooijen 2009). It is based on the assumption that the number of new species found per search day is proportional to the number of as yet undiscovered species, in mathematical terms: dYldt = c {A-Y) where A
. Bonn zoological bulletin. Zoology. Estimating herpetofaunal species richness 5. Fig. 2. A: Heosemys spinosa (Gray, 1831); B: Kaloula pulchra Gray, 1831; C: Naja sumatrana (Mtiller, 1890); D: Tropidolae- mus wagleri (Boie, 1827). 2005). Four models were fitted to the rarefaction curve. The first corresponds with a negative exponential model (Colwell & Coddington 1994; Flather 1996; Van Rooijen 2009). It is based on the assumption that the number of new species found per search day is proportional to the number of as yet undiscovered species, in mathematical terms: dYldt = c {A-Y) where A is the total number of species present in the area under investigation, Y is the to- tal number of species found and c is a constant. This equa- tion can be represented as a negative exponential function ( Van Rooijen 2009): Y=A (\-erct). The basic assump- tion underlying the negative exponential model (hence- forth NE) may be overly simplistic given that abundance patterns are usually strongly skewed ( Lloyd et al. 1968; Coddington et al. 1996; Limpert et al. 2001; Longi- no et al. 2002; Thompson et al. 2003). In order to model more complex species accumulation processes, the NE can be refined in various ways by adding one (d) or two pa- rameters (d and p), resulting in the Chapman-Richards model (henceforth CR), 3- and 4-parameter Weibull cu- mulative distribution functions (henceforth 3pW and 4pW): Y A{\-e-«) (CR), Y=A(l-e<c')d) (3pW), Y = A (\-e-M'-p))d) (4pW) The four models were fitted to the sample-based rarefac- tion curve using nonlinear regression analysis ( Noru- sis and SPSS 1994) with SPSS (release 14 February 1996; SPSS Inc.). Extrapolation using different models for the species ac- cumulation process can provide different asymptotes and thus predict different values of species richness ( Col- well & Coddington 1994; Flather 1996). Therefore, care has to be taken to select the most appropriate model in or- der to minimize bias. In this stud
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