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On the clock: new technique improves precision of extinction predictions by giving a timeframe

August 13, 2013

55231_origThe Salt Creek pupfish, found in Death Valley National Park in California. A new BioFresh study predicts the Death Valley river basin may lose one or more of its few fish species to climate change within the century. Source: Encyclopedia of Life. Author: Jason Minshull

Predicting which species will be the casualties of climate change is a challenging task – but forecasting extinctions within a policy-relevant interval is even more difficult. Studies often use habitat loss to predict how many species will go extinct, but not how long that process will take.  An important new BioFresh study lead by Pablo Tedesco and colleagues and reported in the Journal of Applied Ecology tackles this problem head-on. By building a modelling technique that predicts riverine fish extinctions by 2090, the study develops a meaningful timeframe for policy. A key finding is that climate change may have little effect in most rivers in the next 80 years, especially when compared to other anthropogenic impacts.

To develop effective actions and targets, policymakers need information about extinction threats within a relevant time-scale: the time between prediction and extinction represents a “window of opportunity” where species may still be saved. The EU’s Biodiversity Strategy to 2020 specifically aims to reverse biodiversity loss, as does Aichi Target 12 under the Convention on Biological Diversity, which calls for preventing the extinction of known threatened species. Good planning also means figuring out which threats are the most urgent.

To determine how climate change drives extinctions, researchers have relied on the so-called “species-area relationship” – the greater the area, the more species will be found there. By estimating how much of a particular habitat area will become unsuitable due to climate change, scientists can predict how many species will also eventually disappear. But the time lag can range from decades to millennia, which limits its usefulness for policy. BioFresh partners Pablo Tedesco and his colleagues, however, build on previous work that calculates the relationship between area and true extinction rates. They use that relationship to estimate how habitat loss from climate change will change extinction rates in over 90,000 river drainage basins worldwide, and then predict how many species will be threatened with extinction in a smaller set of the rivers by the year 2090.

The good news for fish is that overall, these new models predict that even under a “pessimistic” climate change model, less than one-quarter of the drainage basins should lose habitat. On average, those basins that do are predicted to have around a 24% higher extinction rate. The effects should concentrate in arid, semi-arid, and Mediterranean climates, especially in the southwest USA, Mexico, southern America, northeast Brazil, northern and southern Africa, southern Europe, western and middle Asia, and Australia. Using actual species numbers, the study found that only 20 out of 1,010 basins would lose species by the year 2090, with the number of species lost ranging from 1 to 5.

Robe_river_australiaExtinction rates in Western Australia’s Robe river basin are predicted to accelerate by over 340%, translating to about two species in the next 80 years, as the river loses water to climate change. Source: Wikimedia Commons. Author: SyntaxTerror

These findings give climate change a much smaller role in driving extinctions than in other studies – particularly when compared to other anthropogenic pressures. In Central and North America, human impacts have driven 47 species extinct over the last century in 20 river basins, a rate 130 times greater than that predicted for climate change.

Although Tedesco and his colleagues point out that other effects of climate change could also drive extinctions, such as rising water temperatures or changing seasonal variability and extreme events, they stress that ongoing factors such as habitat degradation, overexploitation, eutrophication and invasive species are more pressing. Such immediate issues feature prominently in existing international and national policy; for example, a dedicated legislative instrument on invasive alien species is due to be adopted this year under the EU Biodiversity Strategy. “There still is a chance to counteract current and future fish species loss [by] focusing conservation actions on the other important anthropogenic threats generating ongoing extinctions in rivers,” comments Tedesco.

*Tedesco PA, Oberdorff T, Cornu JF, Beauchard O, Brosse S, Dürr HH, Grenouillet G, Leprieur F, Tisseuil C, Zaiss R & Hugueny B (2013). A scenario for impacts of water availability loss due to climate change on riverine fish extinction rates. Journal of Applied Ecology (online).

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