Fossil Record Helps Determine Extermination Risk In Marine Animals
October 24, 2012

Fossil Record Helps Determine Extermination Risk In Marine Animals

Brett Smith for - Your Universe Online

Conservationists have warned for years that rare species have the highest risk of becoming endangered or extinct, but the word “rare” could have several different meanings with respect to the distribution of particular species.

An international team of researchers from Stanford University in California and Humboldt University in Berlin decided to parse the definition of “rare” with respect to conservation and found some animals that many be plentiful in number, but restricted to a small geographic range are more susceptible to population devastating events.

After examining over 500 million years of marine species in the fossil record, the researchers found certain populations of rare marine invertebrates with small geographic ranges were particularly hard hit over the course of history.

"If the patterns we observed in the fossil record hold for species living today, our results suggest that species with large populations but small ranges are at greater risk of extinction than we might have expected," said study co-author Paul Harnik of Department of Geological and Environmental Sciences at Stanford.

In the study, the researchers were able to define "rare" in seven different ways based on: range around the world, size of habitat, and size of population. For example, false killer whales are considered rare because they have a small population, yet can be found throughout the world; while erect-crested penguins have a considerably large population, but can only be found on remote islands off the coast of New Zealand.

While geographic range played the biggest role in determining the risk levels of rare populations, the size of habitat played a secondary role. The combined effect of these two factors is that the animals in the study which had the smallest ranges and habitats were six times more likely to become extinct than other animals. The size of a population was found to be the least determining factor in marine species survivability.

"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 in a press release.

The researchers focused their study on marine animals because the data has been harder to collect in an aquatic environment, leading to less knowledge surrounding these creatures.

Prevailing theories have also asserted that marine creatures are more insulated from extinction events than land animals. However, climate change and human activities may be shifting more risk onto sea-dwelling species, the researchers noted.

According to the report, the results of this study are fairly robust and stand up well to alternate calculations and treatments. This allowed the team to assert that any one major extinction event did not sway their results in any one direction.

"The findings don't mean that when populations dwindle we shouldn't worry about them," Harnik added.

"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."