![]() 3 A) is at first linear and then climbs steeply starting at about a 60–70% disturbance level, suggesting that there is a tipping point for this one group. Loss curves vary in shape in addition to scale, pointing to real biological differences among groups that have implications for conservation. The term “global diversity” is used here to mean the overall richness estimate obtained by pooling all the local-scale species lists. Increasing the level of disturbance would have strong effects on the global diversity of individual groups ( Fig. However, global-scale Chao 1 and λ 5 estimates are extremely similar, and none of the results depend qualitatively on the choice of methods. Analyses presented in the main body of this text focus on the λ 5 method because it is particularly accurate when counts of individuals are uneven. The second, called the “λ 5” or “lambda-5” extrapolator, has not been reported previously. The first method ( 26), called “Chao 1” when applied to within-sample data and “Chao 2” when applied to among-sample incidence data, is very well-known ( 27). One of these is called “shareholder quorum subsampling” ( 24) or “coverage-based rarefaction” ( 25), and the other is called “multiton subsampling.” The other two methods extrapolate the total number of species by considering counts of those found exactly once or twice. Two are analytical subsampling methods that seek to make samples comparable by drawing them down to the same completeness level based on expected counts of species sampled exactly once. Four different approaches are used in this paper ( Methods). However, the compression problem can be solved using methods of either interpolation or extrapolation. Finally, although important meta-analyses of local data have been carried out, most have used raw species-richness values ( 6, 7, 20), and no study has attempted to compare local and global species richness based on strictly comparable estimates that are controlled for sample-size effects. ![]() 19), most researchers have also tended to focus on trees, mammals, birds, and a few other groups such as dung beetles (e.g., ref. 6– 8, 16– 18, and local-scale analyses reviewed in ref. With a few important exceptions (e.g., refs. These methodologies yield disparate results and have individually come under strong criticism ( 15). Even the underlying estimates of global diversity in certain groups have depended on indirect extrapolation methods of various kinds, such as scaling up from local-scale plot data ( 14) or from richness ratios between taxonomic levels ( 15). ![]() Actual extinctions are well-documented only for vertebrates ( 13). Instead of using sample data, global estimates of potential species extinction have tended to rely either on expert opinion ( 4) or on extrapolations that combine observed species–area relationships with expected or actual deforestation rates (e.g., refs.
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