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What is the
evidence for changes in migration patterns, movements, and extinctions
of North American birds and butterflies? What is the relationship between
climate change (warming) and the changes described above? What are the
ecological and societal consequences of these changes? What are the
ecological and practical implications of land use, urbanization, and
development in the face of the changes described above?
INTRODUCTION:
Dr. H. Ronald Pulliam
Science Advisor to the Secretary of the Interior, the Honorable Bruce
Babbitt, Washington, DC
SPEAKERS:
Dr. Terry L. Root
Associate Professor, School of Natural Resources and Environment, University
of Michigan, Ann Arbor, MI
Dr. Camille Parmesan
National Center for Ecological Analysis and Synthesis, University of
California at Santa Barbara, CA
OVERVIEW
Global warming would be
expected to cause the normal range for any particular species to shift
both northward and upward in elevation. This prediction comes from the
fact that such range shifts are well-documented for climate changes
that occurred during the many glacial (ice-age) and inter-glacial (warm)
periods of the Pleistocene (i.e., the last few million years). For example,
when the Earth was warming up after the last ice age peaked around 20,000
years ago, scientists have been able to see (in the fossil record, in
pollen samples from ancient lake bottoms, etc.) that species that were
mobile enough to move northward and upward in elevation did just that.
Species that could not keep pace with the climate changes became extinct,
either because their mobility was insufficient to keep up with the rate
of habitat change, or because suitable habitat was not available in
more northern areas. Both global temperature analyses and continental
U.S climate analyses indicate that modest but significant warming has
occurred during this century, thus it is essential to look at how animal
and plant species and ecosystems are responding.
We are constantly learning
more about how our planet�s ecological puzzle fits together. History
has shown just how complex natural communities are and how interdependent
plants and animals are. For example, eradicating the wolf populations
in the lower 48 States has indirectly contributed to the decline of
dabbling ducks, a consequence that the U.S. Government has spent much
effort trying to reverse. The elimination of wolves in the lower 48
States prompted an increase in coyote populations, which mobilized eradication
efforts causing declines in the coyote populations, which in turn resulted
in surprisingly large populations of red foxes, which are effective
predators of dabbling ducks. Accounting for such complexities of nature
is essential to generating more rigorous forecasts about the possible
consequences (e.g., decline in dabbling ducks) that various actions
(e.g., eradication of the wolf) may create. Such examples make clear
that understanding how changes in fluctuations in climate have influenced
plants and animals over past decades and centuries can help provide
society with an understanding of the possible ecological consequences
of predicted global warming over coming decades and centuries. Such
scientific information will provide managers and decisionmakers with
a firmer basis for making important policy decisions.
The Case
of North American Birds
Using the National Audubon
Society�s Christmas Bird Count data, Dr. Terry Root has been able to
show that, over North America, the northern limits of a majority of
bird species are strongly associated with various climatic variables
(e.g., winter temperature). Further analyses have revealed that both
the ranges and the abundances of birds shift, on an annual basis, in
concert with temperature. Indeed, in another study, Dr. Root and colleagues
have shown that a significant number of migrating birds are arriving
in northern Michigan up to 21 days earlier now than they did in 1960.
Apparently, many bird species can and do respond to changing climatic
conditions. These birds, however, having ranges limited by vegetation,
will probably not be able to shift their ranges with the changing climate,
at least not until the vegetation itself shifts. Consequently, natural
communities of birds could be torn apart, thereby possibly resulting
in a disruption of Nature�s ecological checks and balances until or
unless new ones can be established.
The Case
of Butterflies in Western North America
Because butterflies are
very sedentary, each population has evolved very specific adaptations
to its local habitat. These insects only just manage to fit their life
cycle into the 8�12 week window of time when their host plants are edible.
This window can occur from March to August, depending on the exact locality.
Any long-term climate change is likely to affect the length of this
window, and either cause the population to do really well (if, for example,
caterpillars can have a longer growth period) or go extinct (if, for
example, caterpillars have an abbreviated growth period). As a consequence,
studies on sedentary butterfly species indicate that, in general, butterflies
are very sensitive to climate changes.
Dr. Parmesan�s work on
the biogeography of Edith�s Checkerspot has shown that the level of
population extinctions is four times as high at the far southern end
of its range (in Mexico) than at the far northern end of its range (in
Canada). Extinctions are also about two and one-half times as great
at lower elevations as compared to populations above 8,000 ft. This
skewed pattern of extinctions is effectively shifting the range of the
butterfly both northward and upward in elevation.
Although her work on butterflies
incorporates the most complete data set to document this type of range
shift, other (smaller) studies from around the world are also indicating
northward movement of species� ranges. If studies on the ranges of dissimilar
species over many geographic regions continue to reveal similar trends
and patterns, then a conservative conclusion would be that the currently
detected levels of global and regional warming are affecting the ability
of organisms to live in their traditional habitats. Based on the response
of butterflies to past changes and fluctuatuations in climate, Dr. Parmesan
and colleagues predict that those species that cannot move to new habitats
to keep pace with climate change will die out. These changes will be
exacerbated because the existence of new habitat for butterflies to
move into is likely to be much more severely limited than during historical
climate shifts because potential habitats are being rapidly taken over
by humans, particularly by urbanization and changes in the natural landscape
for agricultural purposes.
Biography of Dr. Terry
L. Root
Dr. Terry L. Root is an
Associate Professor in the School of Natural Resources and Environment
at the University of Michigan and an intermittent employee of the U.S.
Geological Survey�s recently created Biological Resources Division.
Dr. Root�s work has focused on large-scale ecological questions addressing
factors shaping the ranges and densities of animals, primarily birds.
Because climate was found by Dr. Root to be such an important factor
in shaping the ranges and densities of birds, she has incorporated her
findings in helping to forecast the possible consequences global warming
may have on animal communities. In 1990, she received the prestigious
Presidential Young Investigator Award from the National Science Foundation.
In 1992, she was one of 10 individuals selected worldwide as a Pew Scholar
in Conservation and the Environment. Both honors underscored Dr. Root�s
work in basic research, her application of that work to complex real-world
problems, her ability to work at the cutting edge of research requiring
interdisciplinary effort, and her outreach to decisionmakers and the
general public. She received her bachelor�s degree in Mathematics and
Statistics from the University of New Mexico, after which she worked
as a scientific programmer at Bell Laboratory and on NASA�s Voyager
Project. Upon returning to school, she obtained her master�s degree
in Biology from the University of Colorado in 1982, and her Ph.D. in
biology from Princeton University in 1987. After serving a short post-doctoral
fellowship at the Museum of Zoology at the University of Michigan, she
accepted an Assistant Professorship at the School of Natural Resources
and Environment.
Biography
of Dr. Camille Parmesan
Dr.
Camille Parmesan is currently a post-doctoral fellow with the National
Center for Ecological Analysis and Synthesis at the University of
California at Santa Barbara. Her research has focused on multiple
aspects of population biology, including the ecology, evolution,
and behaviors of insect/plant interactions. Dr. Parmesan has been
investigating Edith�s Checkerspot butterfly since 1982. Since that
time she has continued to work, in varying capacities, on both laboratory
and field projects centered around the population biology of this
butterfly. She has also been the recipient of a National Science
Foundation fellowship as well as a NASA Global Change fellowship.
Dr. Parmesan received her bachelor�s degree in Zoology from the
University of Texas at Austin in 1984, and later received her Ph.D.
in Biological Sciences from the University of Texas at Austin in
1995.
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