It is possible to produce a model that predicts both the total loss ofspecies as well as the current rates ofspecies extinction based on the distribution ofnarrow endemic species and estimated rates of deforestation. Twenty-one taxa covering 17 orchid genera were selected and their distributions in terms of recorded localities were determined. These taxa covered 1,421 species of which 539 (37.9%) were narrow endemics found in only one restricted locality. An additional 268 (18.8%) and 163 (11.5%) species were reported from only two and three localities, respectively. Values for species occurring at more than three localities were not considered. The estimated global forest conversion rate used was 0.7% per year, with 45% of tropical forested lands having been cleared at the present time. Using 25,000 as the total global number oforchid species one can estimate that 5,477 (21.9%) ofthe orchid species have been lost at the present time, and ofthe remaining species, approximately 55 will be lost eachyearifcurrentforest conversion rates continue. Madagascar may be an ideal case to test this model. The island's orchid flora is relatively well known and thought to contain about 1,000 species. Analysis of eight taxa showed that 62% were reported from only one locality, 17% from two localities and 7% from three. Using the recent estimate of the 66% total loss (Green & Sussman, 1990) for eastern rainforests for the entire island, the model predicts that 503 species are already extinct. Using the more common estimate of90% forest loss, nearly threequarters (747 species) ofthe island's orchid species should now be extinct.
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