an article on ecosystem - "Ecosystem consequences of extinction different than thought"

The loss of seemingly inconsequential animal species from the sea floor has given scientists a new insight into ecosystem impacts that occur when species become extinct.

An international team of scientists – led by the University of Aberdeen - have found that the consequences of biodiversity loss could be very different to what was previously thought.

Researchers say this is because they have discovered that it is the cause of extinction and order in which species are lost - rather than simply the number of species that go extinct - which ultimately determines the ecological impact of extinction.

Rapid changes in biodiversity are occurring globally, yet the ecological impacts of diversity loss remain poorly understood.

Marine coastal ecosystems are among the most productive and diverse communities on Earth and are of significant importance to the regulation of climate, nutrients, and the food chain.

However, the contributions that coastal ecosystems make to these ecological processes are compromised by man’s activities, such as overfishing, habitat destruction and pollution.

Bottom dwelling marine organisms are particularly vulnerable to extinction because they are often unable to avoid disturbance. These organisms are important because they churn up sediments from the bottom of the ocean – a process referred to as bioturbation - which results in nutrients being returned to the water column where they are vital for other species in the food web.

Dr Martin Solan, from the University of Aberdeen’s Oceanlab, led the research which involved collaborators from America and Canada. He said: “Organisms living in the seabed, such as clams, worms and shrimps may not seem that important, but they are essential for regulating and recycling the planet’s resources.”

Scientists have discovered that the effects of extinctions in general can differ from what they had previously predicted. This is because the characteristics of a species that most greatly influence vital ecosystem processes, such as bioturbation, often also determine susceptibility to extinction.

Dr Solan said: “Our findings suggest that previous predictions of what happens to an ecosystem following extinction may be, for better or for worse, far from the reality.”

Current predictions of what happens to an ecosystem following extinction have assumed that species are lost completely at random. This is not necessarily the case - some drivers of extinction target particular attributes of certain species more than others.

Dr Solan added: “We have known for some time that there are general ecological consequences of species extinction. What we didn’t appreciate is that the point at which bioturbation loss begins, depends on both the cause of extinction and, critically, the order in which species are lost”.
The research team based their findings on communities of invertebrate species (like clams, shrimps, worms) from marine samples collected in Inner Galway Bay, Ireland.

The team used the Galway data to mathematically simulate the random extinction of species versus non-random extinctions - where species were lost according to how rare, big or sensitive to pollution they are. These characteristics matter because they are important for determining the degree of bioturbation.

The team also defined how an ecosystem may respond to extinction. The best case scenario assumed that surviving species altered their bioturbation behaviour in order to compensate for the species which had become extinct. The worst case scenario assumed the surviving community failed to respond.

Dr Solan said: “We chose these alternative scenarios of extinction in order to mimic as closely as possible the full range of consequences that known extinction drivers may have on the communities of the marine environment.

“However, our findings are equally applicable to other ecosystems where the cause of extinction targets particular biological characteristics.”
The team’s findings have important implications for the conservation of biological resources and habitat.

Dr Solan added: “If we wish to predict the ecological impacts of extinction, we must first understand why species are at risk and how this risk correlates with the role they play in the ecosystem. It is only when we know these details that we can hope to effectively protect our ecological heritage.”

The team’s findings Extinction and Ecosystem Function in the Marine Benthos appear in the Journal Science.

The research team included the University of Aberdeen; University of California; Ohio Wesleyan University, Delaware; University of Maryland Center for Environmental Science; University of Washington and University of British Columbia.

http://www.abdn.ac.uk/mediareleases/release.php?id=54