Camilo Mora, a marine biodiversity expert at the University of Hawaii at Manoa, agrees that the sample is too small to make generalizations. “It’s like using a thermometer to measure the temperature at the beach and expecting that that reflects the temperature of the entire ocean,” he says.
Others expressed more fundamental concerns with applying the IUCN criteria to invertebrates. Last year, Pedro Cardoso, an entomologist at the Finnish Museum of Natural History in Helsinki and his colleagues studied 48 species of arthropods and spiders, and found that most species for which there were sufficient data would be classified as threatened owing to their limited geographic ranges on islands and low dispersal abilities. “With the current thresholds, it’s hard to say something about the status of most invertebrate species,” he says.
Collen responds that the IUCN criteria have been successfully applied to a wide range of species and that it is vital to have a consistent scheme. Even if a species has persisted for millennia on a small island, it just takes one commercial development to wipe it out. “We see that in the extinction record,” he says. “These are ephemeral places.”