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Online Only: Populations in flux

U of C researcher looks at ponds to figure out the bigger picture

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Ecological populations are very similar to different people's moods. Some populations are stable and consistent, others display large periodic variations and some are chaotic and fluctuate randomly. Ecologists have been trying to figure out why these variations take place in ecological populations for a number of years.

There are a great many different things that can influence population cycles, ranging from competition between species to environmental conditions like temperature, to the presence of disease agents and pathogens. University of Calgary professor Dr. Ed McCauley has been researching how population variations respond to these different conditions. His findings were published in Nature on Oct. 30.

"The work that I do in part is highly theoretical and it uses mathematical models to discover these features and to understand how these features cause population fluctuations," said McCauley. "On the other hand our research allows us to take that theory and apply it to try to explain what we see in natural systems."

McCauley's research is focused mainly on aquatic systems because of the short generation time of organisms and the ease of manipulating the environment. It involves the small crustacean Daphnia and the microscopic plankton that they feed on. McCauley described the Daphnia-plankton relationship as a central part of the food chain in lakes and ponds throughout the world.

"If you look at most of the climate models for western north America, although they disagree in the details, in general they predict that there will be a three to four degree temperature increase over a wide area," said McCauley. "If there is going to be this temperature change, then shallow prairie aquatic systems are going to be one of the first systems that will respond to that temperature change because they're shallow, therefore they don't have a lot of volume to buffer these atmospheric changes."

The predicted temperature change is expected to change the rate of sedimentation of carbon in small aquatic systems. One of McCauley's graduate students, Kyla Flanagan, found that these changes could transform ponds and lakes into carbon sources instead of sinks, depending on the interaction between changes in the food web and sedimentation rate.

McCauley's research has lead him to the conclusion that as temperature increases small aquatic systems tend to have more unstable populations.

A number of small fish feed on Daphnia. As Daphnia populations become less stable so do food sources for small fish with consequences all the way up the food chain. As climate conditions change it will become increasingly important for ecologists to predict how different systems will react.

"It's that added component of variation that is really tough, but it's the one that we need to go after," said McCauley. "It explains things like population persistence so whether or not a population is actually going to go locally extinct."

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