Endangered species such as the Atlantic cod, would rank highly using the new method, say researchers, as they have connections with many other species.
Credit: Arkive
SYDNEY: Simple mathematics, used by Google to rank websites, is now being applied by biologists to determine the importance of species for conservation.
When a species becomes extinct, it can have a knock-on effect - something like falling dominoes - that causes other species to die out too. The new technique, reported in the journal PLoS Computational Biology helps to pinpoint those species that are crucial to the survival of ecosystems.
"The key to our study is that the conservation of a species cannot be considered on its own. The existence of one species depends on its connections with all other species within an ecosystem," said lead author Stefano Allesina, an ecologist at the University of California, Santa Barbara, in the USA.
Connections and hubs
Typically, conservation studies focus on one species at a time. But some studies look at a species and the number of connections or 'hubs' it has with other species in the ecosystem.
Allesina and his coworker Mercedes Pascual, an evolutionary biologist at the University of Michigan, in Ann Arbor, took this approach one step further by looking at all of the connections between the species in an ecosystem.
"What we want to show is that all species are important, even those with few relationships with others, and rather, you need to consider its position within these networks of relationships before identifying its importance in the ecosystem," explained Allesina.
Using a clever application of linear algebra, the researchers adapted Google's 'PageRank' algorithm for ranking websites to instead rank the importance of a species to the survival of an ecosystem.
High ranking species
In simple terms, PageRank rates the importance of websites and ranks them in a list compared to other websites. Sites with a higher ranking are those that are linked to more often by other sites and therefore have a greater number of connections.
Adapting this approach to ordering the web of connections within an ecosystem allows species to be ranked in importance by virtue of how many other species are linked to them.
One example of species that depend on each other are the overfished Atlantic cod (Gadus morhua) and other smaller animals that descend from it in the North Atlantic food chain. Because the predator has been depleted, species including smaller pelagic fish and northern snow crabs have boomed and are themselves depleting populations of phytoplankton and zooplankton.
Allesina said the significance of prioritising species for conservation is that when resources are limited, researchers can target those resources where they are needed most.
Fraser Torpy, microbial ecologist and statistician from the University of Technology in Sydney, Australia, said the study is "very useful adjunct to our ability to determine what makes a species important in terms of its position in its ecological community".
However, he cautions that the method may only work for simple food webs. "Whilst [this is] an innovative and genuinely useful novel technique for endangered species assessment, it must be remembered that the true complexity of real ecosystems cannot be overestimated."
Allesina agrees that the approach has limitations, but said it provides an alternative method to help us approach conservation problems.
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