Ecological correlates of threatened endemic island rodents

Some of the ecological correlates of threatened endemic island rodents across 31 main islands/archipelagos worldwide are studied. Overall, there were 83 entirely endemic genera and 197 endemic species, with the number of both endemic genera and species positively correlating with (log) island size. Twenty-seven rodent genera, and 49 species, endemic to islands, are threatened with extinction, with the Oriental region housing the highest numbers of endemic threatened taxa. There was a significant positive relationship between (log) island size and number of threatened endemic species. The number of endemic species per island was also significantly positively correlated with the number of threatened species per island. A logit model revealed that the probability of the presence of at least one threatened endemic species was 0% for islands below 1560 km², and 80% for islands sized about 3120 km². The mean body weight of endemic threatened taxa increased significantly with increases of (log) island size (r=0.144, n=12, p=0.0096), and was particularly high in the Caribbean islands. Our study indirectly supported the notion that species linked to habitat fragments (=islands of remnant habitat) are more prone to extinction than species able to traverse suboptimal habitats (=seas of unsuitable habitat). Our results also demonstrated that the number of threatened endemic species per island was dependent on the total number of endemic species in each island, thus showing that tropical islands may be more prone to include assemblages of threatened endemic rodent species than temperate islands. Endemic species inhabiting islands of about 1500 km²are of immediate conservation concern because of their high probability of becoming extinct in the years to come, given that their counterparts from even smaller islands are already extinct since decades or hundreds of years ago.