Researchers craft model that provides reasons for climate-change observations

December 18, 2000

A first-ever study by a Penn State researcher creates a model incorporating biological factors to quantify processes behind ecological responses to climate change, moving the field of study beyond its previous observational limits and providing a way to analyze what contributes to the earlier timing of spring events.

A paper published in the 7 January issue of Proceedings of the Royal Society of London, B by a team led by Eric Post, assistant professor of biology at Penn State, reveals flowering plants in Norway bloom earlier after warmer winters. More importantly, the paper provides a model for why that occurs.

Using data for three species of flowering plants collected during a 50-year period, Post and his collaborators applied a mathematical and statistical approach developed originally for statistical studies of population dynamics to their data about plants. The model incorporates variables such as competition for resources and population density, which, the authors emphasize, are also factors likely to change with climate.

In each of the species--wood anemone, hepatica, and colt's foot--the model shows plants bloomed earlier after warmer winters because of interactions between competition, climate, and resources. Researchers studied 26 different populations using data collected from 1928 to 1977 at observational sites organized by botanist K.H.O. Printz and his successors in Norway. That information included dates of flowering, outside temperature, and other factors regarding each species.

"We hear with increasing frequency reports about birds nesting earlier and flowers blooming sooner," Post said. "Those reports get a lot of attention because they provide convincing evidence that species are responding to climate change. But, if we really want to understand what's happening, and make predictions about what will happen with future climate changes, we need to get at the mechanisms and relationships behind the changes."

While the results might be expected, based on observations of other species and a growing acceptance of climate change, the researchers were pleased because their model provided additional insight. Along with observations of the changes, the researchers produced an answer to why the earlier blooming occurred.

"It was not just a direct effect of climate change," Post said. "There are other factors involved, such as resources and competition, that tell you a little bit more about what happens when it gets warm. It's not that cold temperatures simply constrain things. Temperature affects things the individual organism has to deal with in its own life history."

In developing the model, a process that took nearly two years, Post and his collaborators worked to determine variables that applied to their work and allowed for interpretation and use by other researchers studying other species. As others use the model, Post believes the scientific community can learn even more about climate change. While he expects a mix of acceptance and skepticism for the model, he looks forward to seeing the results of its application with other species.

"You want the model to be simple, powerful, and easy to use," Post said. "You have to provide a set of terms and let others define what they mean for the system they're using. For example, 'resources' was intentionally vague for us because we wanted our model to apply to any system, even large mammals, when 'resources' might be the physical condition of the females who were reproducing or the availability of forage. Still, you don't want to have a lot of variables because that's not a very applicable model."

As a result, Post and his collaborators believe they have crafted a model with great utility that provides a tool for a new approach to the study of ecological responses to climate change.

"It's an important development in terms of climate-change ecology--it's like going a step further," Post said. "Now we have a framework to really quantify the way ecological systems respond to climate change. That's necessary if you want to make predictions about the effects of climate change."

This research was supported by the National Science Foundation. Collaborators with Post were: Terry V. Callaghan of the University of Sheffield, England, and the Abisko Scientific Research Center, Sweden; Mads C. Forchammer of the University of Copenhagen, Denmark; and Nils Chr. Stenseth of the University of Oslo, Norway.
CONTACTS: Eric Post 814-865-1556/
Steve Sampsell (PIO) 814-865-1390/

Penn State

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