Can a population evolve to survive?
Active Listening Questions: • What are the qualities found in individual butterflies that are successful colonizers? • Can climate change directly lead to the formation of a new gene? W H A T: In this clip from the 2005 presentation “Impacts of Changes in Extreme Weather and Climate on Wild Plants and Animals,” biologist Camille Parmesan explains how warming climates may be leading to a change in genetic ratios in populations of Edith’s Checkerspot Butterfly. In populations that have successfully settled in new areas (dispersers), more of the butterflies had high ATP and large flight muscles than did populations that had lived in the same area for a long period of time. In response to a question from the audience, Dr. Parmesan explains that although populations may evolve to be better dispersers over the short term, because dispersers have low reproductive rates, the ratio of dispersers to sedentary individuals will likely shift again once a new population has been established. H O W : Population genetics are studied by observing visible physical characteristics of individuals in a population or by analyzing cells to search for a specific genetic sequence. “You’re trading off
ability to find a new
place with an ability to
make kids.”
W H Y: Studies such as Dr. Parmesan’s require on-­‐the-­‐ground observation and, sometimes, capture of butterflies in remote mountain locations. Because she needed to be able to compare her own results with previous observations of populations similar to or the same as those studied by others, Dr. Parmesan’s ground study locations were determined by where she had data from previous experiments. SO W H A T: 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 suggest that some species may be able to adapt or evolve on a population level in order to survive these changes. Understanding which species are likely to be able to survive on their own and which are at risk for extinction is important for scientists and decision-­‐makers who want to preserve biodiversity. BIO: Dr. Camille Parmesan is a professor of Biology at the University of Texas in Austin. She has a PhD in biological sciences and an interest in a broad range of topics. She began her research in ecology, evolution, and butterfly-­‐plant interactions before gravitating toward the investigation of the impact of climate change on butterflies. From the Horse’s Mouth
Can a population evolve to survive?
TA KIN G TH E REIN S: reflection
D iscussion Q uestions: Discuss with a friend or record your thoughts in a journal. • What is the connection between climate change and the frequency with which the dispersive phenotype is found? • Because they reproduce over a short time-­‐span, insect populations, such as butterflies, have the ability to evolve rapidly. Do you think that other types of animals, such as mammals, may be able to evolve rapidly enough to survive regional changes in their ecosystems? Why or why not? Quiz Questions!
Quiz 1. Which of the following characteristics was NOT commonly found in successfully dispersive butterflies? a. Longer antennae b. Higher levels of ATP c. Lower reproductive success d. Bigger flight muscles Clip Activity:
Modeling Population Evolution record this activity in your science journal Imagine a butterfly population that lives in an area where spring conditions now occur too early for
caterpillars to survive well. What will the genetics of this population look like next year? •
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Imagine a population of 1,000 butterflies. In this population 80% of the butterflies are good reproducers (sedentary). 20% of the population are good flyers (dispersers). These are much smaller numbers than is realistic, but for the purpose of this exercise, we will use a simplified example. Caterpillars of both types of are equally likely to hatch. After the first year, 100 butterflies from the colony fly out to colonize a higher location where spring conditions do not come early. 80 are sedentary and 20 are dispersive. Of these 100 butterflies, only 10/80 sedentary and all 20/20 dispersive butterflies make it to a higher location. How has the population ratio changed from the original location? Each year, the sedentary butterflies lay 4 eggs each and the dispersers lay only 2 eggs each. In the new location, if all of the settler butterflies die after laying their eggs and all of the eggs hatch, what will the new ratio of dispersers to sedentary butterflies be at the end of the next summer? How long will it be before the ratio is similar to what it was in the original population (~80:20)? What about this scenario is natural? What about this scenario is unnatural?
From the Horse’s Mouth
Can a population evolve to survive?
Taking the Reins: Further Activities
G o B eyond
Science Journal 1. Choose one or more of the questions below: a.) Over the course of history, some human populations have been more dispersive while others have been more sedentary. What are some of the pressures that might drive a human population to leave one area and colonize another? b.) Imagine and describe a radical climate change that could occur where you live (shorter winters, less rain, more storms, ect.). Is it better to stay where you are or move to a new location? Why? c.) What causes most shifts in genetic variation (evolution)? 2. Write down or sketch what you think the answer to the question is without looking anything up. 3. Ask a family member, friend, or teacher the same question and write down their answers. 4. What are the common answers you’ve collected? Write or sketch the common themes/ideas. 5. Devise your own strategy for digging deeper (ask a scientists, check out university and government agency websites like NOAA and NASA, go to the library, design and conduct an experiment, ect.) until you are satisfied that the answer makes sense to you. 6. Summarize what is known and unknown about the subject of the question. Also note what evidence there is in supporting what is known and how the evidence was obtained. 7. Rate the answer you’ve come up with on a scale of 1 to 10, 1 being weak with lots of uncertainty, 10 being perfect. Glossary Term: Colonization
When a species spreads to and establishes a successful population in a new habitat. Further reading
Parmesan, C., T.L. Root & M. Willig. Impacts of extreme weather and climate on terrestrial biota. (2000) Bull. American Meteorological Soc. 81: 443-­‐450.