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Is it possible to predict the tipping point of an ecosystem?

Scientists studying a remote Wisconsin lake have identified early warning signs that an ecosystem is on the verge of a radical, rapid change.

Scientists working on a remote Wisconsin lake have identified early signals that warn when an ecosystem is on the verge of a regime shift – a radical and rapid change from one type of ecosystem to another. They hope that understanding this kind of signal will improve our ability to protect and manage ecosystems in the future. The research findings were published in the journal Science on May 27, 2011.

Largemouth bass. Image Credit: US Geological Survey.

Ecologist Stephen Carpenter and his team began their experiment by gradually adding largemouth bass (Micropterus salmoides) to remote Lake Peter in Wisconsin over a period of three years. The scientists hypothesized that the addition of top predators to the lake would cause a decline in smaller planktivorous fish, which the bass prey upon. These changes in the food web were expected to have cascading effects on smaller plants and animals in the lake – the phytoplankton and zooplankton.

EarthSky interview with Stephen Carpenter

Overall, the scientists hypothesized that the addition of a top predator to the lake would disrupt the structure of the ecosystem.

A comparable nearby lake served as the control.

By monitoring the chemical, biological, and physical vital signs of Lake Peter, the scientists were able to observe what ecologists call a regime shift, a rapid change from one type of ecosystem to another. Sorting through the data, they noted two early warning signals that something was amiss with the lake: an increase in the variability of phytoplankton populations and a slowing rate of return from perturbations – that is, when things differed from the norm they tended to stay different longer.

Increases in variability and decreases in resilience have been observed in other ecosystems undergoing catastrophic change. Notably, these same early warning signals were observed during spruce budworm outbreaks that caused widespread deforestation in boreal forests in Canada.

Regime shifts are often nonlinear, surprising, and difficult to reverse. In a press release, lead author Stephen Carpenter stated, “It is like a runaway train once it gets going and the costs – both ecological and economic – are high.”

The scientists hope that by validating early warning signals of ecosystem change in the Wisconsin lake, they can develop effective tools to track and intervene in a wide variety of ecosystems such as rangelands, forests, and marine fisheries before irreversible environmental damage happens.

In the press release, Alan Tessier, program director in the National Science Foundation (NSF)’s Division of Environmental Biology noted:

This research shows that, with careful monitoring, we can foresee shifts in the structure of ecosystems despite their complexity. The results point the way for ecosystem management to become a predictive science.

For humans, the ability to predict when an ecosystem will approach a tipping point could help reduce negative impacts on economies and livelihoods. Future research to validate the use of early warning signals of ecosystem change will likely involve testing the findings described by Carpenter and others in the May 27, 2011 issue of Science in multiple types of ecosystems through the use of data obtained by the NSF’s Long-Term Ecological Research network.

Stephen Carpenter and the 2011 Stockholm Water Prize

Deanna Conners

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