To find out, the team scoured a fossil database for marine invertebrates that inhabited the world's oceans from 500 million years ago to the present a dataset that included 6500 genera of sea urchins, sand dollars, corals, snails, clams, oysters, scallops, brachiopods and other animals.
When the researchers looked for links between extinction rate and measures of rarity, they found that the key predictor of extinction risk for ocean animals was small geographic range size.
Habitat breadth played a secondary role, whereas population size had little effect. The result: Ocean animals that both had small geographic ranges and tolerated a narrow suite of habitats were six times more likely to go extinct than common animals were.
"Environmental changes are unlikely to affect all areas equally, or all individuals at the same time in the same way. If something terrible happens to some part of a species' range, then at least some populations will still survive," Harnik explained.
Life in the sea was once thought to be less prone to extinction than life on land. But with global warming, overfishing, and ocean acidification pushing sea life to its limits, growing evidence suggests otherwise.
"The findings don't mean that when populations dwindle we shouldn't worry about them," Harnik said.
"But the take home message is that reductions in range size such as when a species' habitat is destroyed or degraded could mean a big increase in long-term extinction risk, even if population sizes in the remaining portions of the species' range are still relatively large."
The results will be published this week in the journal Proceedings of the Royal Society B.
|Contact: Robin Ann Smith|
National Evolutionary Synthesis Center (NESCent)