High rates of extinction and threat in poorly studied taxa

Mass extinctions in the past have been characterized by abnormally high species extinction rates within almost all taxa. Attempts to estimate relative rates of extinction and threat among modern taxa, such as insects, plants, and vertebrates, are impeded by differences in the quality, of information about each group. Insects and marine groups, for example, have much smaller percentages of known threatened species but also hate many more undescribed species than do plants ol vertebrates. I tested The possibility that all major groups have equally high rates of extinction and thr ear. The first test was a model assuming that differences ill apparent global extinction and thr eat rate are caused by two sampling biases that produce artificially low rates in understudied taxa. (I) a common-species bias in which taxonomists tend to record common (more extinction-resistant) species first and (2) evaluative neglect, which is a tendency to spend relatively less effort evaluating the extinction and threat status of recorded species in understudied taxa. Global extinction and threat data from a number of groups generally follow the pattern predicted by this model. The second test shows that in direct measurements of extinction and threat between taxa in well-studied regions, such as the United States and United Kingdom, the apparent global disparity among taxa is greatly reduced. Indeed, many globally understood taxa, such as insects and other invertebrates, have higher rates of threat than many other taxa, including mammals, in these well-studied areas. These two tests provide quantitative support for previous suggestions that the wide disparity in rates of species extinction and threat among groups represents an artifactual distortion of the actual rates. Specific suggestions for improved estimates of actual threat include (in order of increasing accuracy): use of well-studied proxy taxa such as mammals; comparison of threat data among taxa only in well-studied regions; and, especially important, increased efforts to evaluate the threat of recorded species of understudied taxa.