Taxonomic selectivity in amphibians: ignorance, geography or biology?

Many taxa, including amphibians, have been shown to have a taxonomically non-random distribution of threatened species. There are three possible non-exclusive reasons for this selectivity: non-random knowledge of species conservation status, clades endemic to different regions experiencing different intensities of threatening process and the effects of clade-specific biological attributes on the susceptibility of species to these processes. This paper tests the sufficiency of the first two explanations using extinction risk evaluations from the 2004 Global Amphibian Assessment. Our results indicate that they cannot alone account for the degree of non-randomness in extinction risk among amphibian families. The overall distribution of threatened amphibians remained taxonomically non-random when species of unknown conservation status were omitted, and significant selectivity was detected not only at a global geographic scale but also in country- and site-specific data sets. Furthermore, the same families tend to be over- or underthreatened within different countries. Together, these results suggest that biological differences among amphibian families play an important role in determining species' susceptibility to anthropogenic threatening processes.