Oxford Martin School

"99.9% of all life is extinct," said Owen Petchey, a researcher at the University of Sheffield's Department of Animal and Plant Sciences. Petchey's seminar titled, "Contagious Extinctions and Ecosystem Collapse," looked at how we understand extinction, both on the level of an individual species and in the broader context of an entire ecosystem.

His talk, the final one in the 21st Century School's Hilary Term series on Complexity and Systemic Risk, served as a book-end to the series opener given by Oxford Zoology professor Robert May, as well as an introduction to the 21st Century School's recently announced Professorship in Biodiversity. In addition, 2010 has been named the International Year of Biodiversity by the UN, which made the topic especially timely.

In order to understand evolutionary biology, Petchey argued, extinction cannot be ignored, even though it can be difficult to say definitively when a species has become extinct. Tracing the history of fossil diversity, he showed that a gradual increase in diversity has been punctuated by periods of mass extinction. Though there are many theories behind these steep downward spikes - such as meteors, climate change, and other external changes in the environment - Petchey posited that one explanation might be a collapse in the internal dynamics of the system. Likening the ecosystem to the game Jenga, he showed how removing one piece of a puzzle can cause the whole structure to topple.

While Jenga can be a useful metaphor for the instability that occurs in a system when one or more species dies out, the practical explanation can be illustrated in terms of food webs - the relationships between predators and prey - and extinction cascades, the indirect relationships between species that share an ecosystem. As an example, Petchey described the near extinction of the sea otter which preys on sea urchins. When sea otters declined, the number of sea urchins surged, and the resultant increase in urchins posed damage to the kelp forest ecosystems on which they feed. By looking at ecological communities and their collapse, one approach to studying extinction focuses on the internal dynamics of systems and their complex interrelationships.

The other way the phenomenon is commonly studied is by analysing the endangerment of individual species - both the environmental drivers and the characteristics of a species that may lead to its extinction. Petchey likened these two approaches to stress-testing the individual components of a car vs predicting the longevity of the car as a dynamic, moving system with multiple interacting pieces. His methods attempt to integrate these two approaches, looking at extinction as both a systemic issue and also examining its constituent parts.

To explore these questions, Petchey and his graduate students use microbial microcosms as a tool for both research and teaching. Using these enclosed ecosystems, their research has shown that extinction is an accelerating process that destabilises an ecosystem and causes further extinction within the system - albeit indirectly. He states, "In the ‘ecological game,' loss of components increases the risk of failure to the remaining components, due to the complex network of indirect interactions among components."

There are still many unanswered questions about how this works and questions from the audience addressed many of these unexplored areas - such as what happens when you introduce/remove predators, add redundancy or suffer a population drop that does not lead to extinction. Through his ongoing work, Petchey continues to bring together these divergent approaches and seeks to gain a better understanding of these mechanisms. He is continuing to pursue funding for this research so we can gain insight on biodiversity before it's too late.

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This blog was written by Susan Curran, Web and Publications Officer, at the Institute for Science, Innovation and Society.