Extinction Debt, Historical Legacy Of Population Losses More Significant Than Current Population Numbers

Extinction debt is playing a considerably more important role in recent extinctions than conservation practices, or the lack thereof, are, new research from the University of Vienna has found. Most recent extinctions are primarily the result of socio-economic stressors placed on environments in the early to mid 20th century, and the population/genetic diversity losses associated with them.

Image Credit: Wolfgang Rabitsch
Image Credit: Wolfgang Rabitsch

This means that the full damage caused to natural environments and biodiversity by the activities of the late 20th century and early 21st century will likely not be completely realized until decades from now. Though they have been inferred, hence the popular name for the mass extinction event that we are currently experiencing, the Anthropocene.

This brings up the reality, that has often been argued, that modern style conservation practices will be ineffective on the longer term, and unable to stop most species extinctions.

Extinction debt, for those that aren’t familiar with the term, is the concept that a species is approaching inevitable extinction as a result of past events. These events may have been habitat loss, loss of reproductive ability, loss of genetic diversity, fragmentation of populations, disruption of food chains, loss of codependent species, etc.

So, in short, nearly everything that people are doing to the world could be thought of as causing extinction debt.

The new study on extinction risk is “based on extensive data from 7 taxonomic groups and 22 European countries has shown that proportions of plant and animal species being classified as threatened on national Red Lists are more closely related to socio-economic pressure levels from the beginning than from the end of the 20th century.”

“It is well understood that the survival of a substantial and increasing number of species is put at risk by human activity via e.g. habitat destruction, environmental pollution or introduction of alien species. Accordingly, the most recent global IUCN Red List classifies 31% of the 65,518 plant and animal species assessed as endangered. However, the temporal scale of cause-effect relationships is little explored. If extended time lags between human pressure and population decline are common, then the full impact of current high levels of anthropogenic pressures on biodiversity will only be realized decades into the future.”

By using a historical approach, “the new study provides circumstantial evidence that such time-lags are indeed substantial. The researchers demonstrate that proportions of vascular plants, bryophytes, mammals, reptiles, dragonflies and grasshoppers facing medium to high extinction risks are more closely matched to country-specific indicators of socio-economic pressures (i.e. human population density, per capita GDP, land use intensity) from the early or mid rather than the late 20th century. Accordingly, their results suggest a considerable historical legacy of species’ population losses. In a related analysis they also show that current spending on environmental conservation only has a weak mitigating effect. This finding implies that current conservation actions are effective, but inadequate in scale, to halt species losses.”

“The broad taxonomic and geographic coverage indicates that a so-called ‘extinction debt’ is a widespread phenomenon,” says Stefan Dullinger from the University of Vienna. “This inertia is worrying as it implies that albeit numbers of species classified as threatened on Red Lists are increasing continuously and worldwide, these assessments might still underestimate true extinction risks,” explains Franz Essl from the Austrian Environment Agency.

Therefore, the researchers state that “mitigating extinction risks might be an even greater challenge if temporal delays mean many threatened species might already be destined towards extinction.”

The new research was just published in the Proceedings of the National Academy of Sciences.


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About the Author

's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy. You can follow his work on Google+.