What is a range shift and why do they happen?

What is a range shift and why do they happen?

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: Here you will find clear descriptions of what you just saw, how they know what they said they knew, why they know it to be trustworthy information. Finally we will ask the question, "So what!" and explore why the information is important.


In this clip from the 2005 presentation “Impacts of Changes in Extreme Weather and Climate on Wild Plants and Animals,” biologist Camille Parmesan describes shifts in location for Edith’s Checkerspot Butterfly as a consequence of extinctions occurring in some populations and not in others. She explains that the extinctions occurred along a shift in the temperature isotherm--a shift where higher temperatures occur further north and at higher altitudes than was previously the case. Further investigation, however, revealed that the butterfly die-offs were not directly related to the isotherm shift but instead were driven by extreme events such as false springs, droughts, or changes in snowpack.


Because she wanted to study population changes over the past 100 years, Dr. Parmesan needed to select a species that had been studied in the past and also lives in a range that had experienced climate changes over the past century. Edith’s Checkerspot Butterfly fulfilled both qualifications. Next, Dr. Parmesan needed information on current butterfly populations. Because the data she needed did not yet exist, Dr. Parmesan obtained this information by performing field studies of her own.


When determining whether or not two variables influence one another, it is important to perform observations to see if the relationship exists or not in real life. The exact cause of population extinctions in Edith’s Checkerspot Butterfly was unknown, so Dr. Parmesan used observations and fieldwork to test the truth of a hypothesis. Initially, it appeared that the isotherm shift was causing the extinctions because the two occurred in the same area. When Dr. Parmesan performed on-the-ground research, however, she discovered that die-offs were in fact driven by extreme events such as droughts leading to a timing mismatch.


Scientific data suggests that the climate is warming. In both apparent and subtle ways, these changes in average temperature will impact where certain species are able to survive.  Studies such as Dr. Parmesan’s can help people to understand the relationship between climate change and population extinction, allowing us to make better decisions about how to preserve valued species.

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Further Reading
Further Reading: 

The complete PowerPoint for this presentation is available on the AGCI website.

Parmesan, Camille and Gary Yohe. 2003. "A globally coherent fingerprint of climate change impacts across natural systems.Nature: 421, 37-42. 2 January, 2003. doi:10.1038/nature01286

complete video of Dr. Parmesan's public lecture on this same topic is available on agci.org.