An international team of scientists, including UBC zoology professor Diane Srivastava, has discovered that the order in which species go extinct -- rather than just the number of species as previously thought -- ultimately determines long-term impact on an ecosystem.
In a study published in the November 12 issue of the journal Science, Srivastava and her colleagues provide a new look at long-term ecosystem impacts by studying the loss of shrimps, clams, worms and other organisms from the sea floor. Such bottom-dwelling marine creatures are particularly vulnerable to extinction because they are often unable to avoid disturbances.
“This represents an important step forward in ecological thinking,” says Srivastava. “Up to this point, scientists had only determined the theoretical relationship between the number of species in an ecosystem and how well it functions.”
At the bottom of the world’s oceans live an astonishing array of animals -- crabs, brittlestars and marine worms -- that play an essential role in regulating and recycling the planet’s resources by churning up and filling the sediments with oxygen (a process called bioturbation).
In a comprehensive survey of 139 sea floor-dwelling marine invertebrates in Galway Bay, Ireland, the team looked at how extensively the sediments are mixed there, matched that with data on species size, abundance and movement through the mud, and constructed mathematical models to predict the ecological consequences of losing species.
They found that the extinction of species is generally expected to reduce the amount of sediment mixing, and consequently diminish the oxygen concentrations that sustain life. The amount of change depends on the order in which species are going extinct as well as the reasons animals are disappearing. This suggests that conservation efforts should focus not only on the seemingly important species, but also on the total variety of life -- including the sediment-churning bottom dwellers -- found in an ecosystem.
“These findings tell us that we need to understand better why and which species are likely to go extinct if we are predict the practical consequences of their loss. Sustaining the valuable services provided by our oceans will ultimately depend on preserving the broad diversity of life that resides there,” Srivastava says.
Marine coastal ecosystems are among the most productive and diverse communities on Earth and they play a significant role in the regulation of climate, nutrients, and the food chain, but rapid changes in biodiversity -- brought on by human activities such as overfishing, habitat destruction and pollution -- are occurring says Srivastava, who collaborated with researchers from the United States and Scotland on the study.
Predicting how coastal environments will cope as animal species decline as a result of human activity will depend on a better grasp of why species are at risk and the role they play in an ecosystem.
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