OK for now, but what about in a hundred years? (Image: Anastasios Sakoulis)

From dragonflies to bears, when it comes to lost species we ain’t seen nothing yet.

Biologists are getting rattled about growing evidence of “extinction debt” – the idea that there is a delay of decades or even centuries between humans damaging ecosystems and the demise of species that live there.

In the largest extinction debt study to date, Stefan Dullinger of the University of Vienna, Austria, ranked 22 European countries according to the proportion of domestic species classed as endangered in the year 2000. He then ranked them for the amount of pressure put on nature in the years 2000, 1950 and 1900 – as measured by population density, per-capita GDP and intensity of land use.


He found that the countries with the most recent extinctions were the ones that put the most pressure on their ecosystems in 1900; pressures applied in 2000 had little bearing.

The upshot is that today’s extinctions may be the result of damage we did in the early 20th century; our own extinction legacy could ultimately be far worse.

Feeling the heat

Dullinger found that small species with short lifespans, such as dragonflies and grasshoppers, are only just feeling the effects of human pressures applied in 1900. The time lag for mammals is shorter – many species are feeling the heat from our actions in the 1950s. This could be because insects can survive in small fragments of natural habitat, says Dullinger, whereas larger species need bigger areas of undisturbed terrain.

One explanation for the findings would be that countries are now better at protecting species. But Dullinger found that the time lag persisted even when he factored investment in environmental projects into his rankings. “The conclusion is clear,” he says. “Biodiversity takes its time to respond to socio-economic pressures.”

This extinction debt could mean that many endangered species are already doomed. The one hope, says Oliver Wearn of Imperial College London, is that predicting likely extinctions could focus “conservation efforts in areas with the greatest debt”.

Journal reference: PNAS, doi.org/k8c