Islands often contain distinctive ecological conditions that can lead to unusual evolutionary trajectories such as dwarf mammoths and giant rats. In new research, scientists from the German Centre for Integrative Biodiversity Research and colleagues looked across living and extinct species from islands to determine whether these evolutionary oddities were more threatened and found that both dwarf and giant species were more at risk for extinction.
Although they cover less than 7% of the planet’s surface, islands are hotspots of biodiversity.
Due to their isolation, they often contain species that have led unique evolutionary trajectories resulting in peculiar features, including unusually large or small body sizes.
For example, islands have hosted dwarf mammoths and giant rodents.
However, islands are also known hotspots of extinction — particularly human-mediated extinction — with species that exhibit extreme body size shifts seemingly at greater risk.
“On the one hand, phyletic giants might provide bigger reward for hunting,” said lead author Dr. Roberto Rozzi, a former postdoctoral researcher at the German Centre for Integrative Biodiversity Research and now curator of paleontology at the ZNS of Martin Luther University Halle-Wittenberg.
“On the other hand, dwarfed species seem to have less deterrence power, facilitating hunting or predation by introduced predators.”
To better understand the relationship between body size evolution and susceptibility to extinction, Dr. Rozzi and co-authors evaluated data on extinct and living island dwarf and giant mammal species and their risk and rate of extinction through time, both before and after human arrival.
They combined data on extinction risk, body mass, and body size change for 1,231 living and 350 extinct species of insular mammals from islands and paleoislands worldwide spanning the last 23 million years.
They found that extinctions and extinction risk were highest among island dwarf and giant…
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