May 11, 2008 An endangered species of flora or fauna ups the risk of the extinction of the other species in its ecological community. Trophically unique species are more vulnerable for cascading extinction, according to studies of a team of theoretical biologists active at Linköping University and the University of Sheffield.
The researchers simulated what happens in a food web when a species dies out, to see which species might die out and what the consequences might be in each case. Findings indicate that secondary extinction gives rise to a greater decline in trophic diversity than can be explained by mere chance.
A jackstraws analogy can be made. In the game of jackstraws, or spillikins, the players try to pull a stick out of a jumbled pile without moving the other sticks. The sticks can represent members of an ecological community. Some species, like some sticks, can easily be moved with no consequences to their neighbors. Others occupy a unique position in the food web and their removal will have a considerable impact on other members.
One instance of this is the sea otter. It lives on mussels and sea urchins, and when it disappeared from the tang forests along the Pacific coastline of the Americas, entire ecosystems collapsed. Many other species in the otter's ecosystem became locally extinct.
The LiU-Sheffield study shows that those species, which disappear in the second wave of extinction, have a trophically unique role. Once these keystone species are identified, conservation activities can be directed where they will help most.
The LiU scientists Bo Ebenman, Anna Eklöf and Charlotte Borrvall together with Owen L Petchey from the University of Sheffield, England, publish their team findings in the journal: The American Naturalist. Their article "Trophically Unique Species are Vulnerable to Cascading Extinction" is also featured in Nature Research Highlights.
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