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Fossil Plant and Insect Communities
 Key to Understanding Global Change
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Pennsylvania State University
February 16, 2003

Denver - Insect damage recorded in fossil plants and the types of 
plants present in the fossil record are helping researchers to 
understand how ecological communities recover from climate change and 
mass extinction events, according to a Penn State paleontologist and 
his colleagues.

Researchers looking at plant communities and insect predation on 
leaves at both the Cretaceous-Tertiary boundary 65.51 million years 
ago and 10 million years later at the Paleocene-Eocene boundary, can 
track the changes in plants and insects through time. The K-T event, 
which marked the extinction of the dinosaurs and more than 50 percent 
of all plant species, was caused by the impact of an extraterrestrial 
object, while the P-E interval was a more gradual change from one 
climate regime to another caused by a long-term global warming trend.

"The early Eocene 52 million years ago was the warmest the Earth has 
been in the last 100 million years, and that warming lasted for 2 
million years," says Dr. Peter Wilf, assistant professor of 
geosciences at Penn State.  "There is strong evidence for high 
diversity when temperatures were warm," Wilf told attendees at the 
annual meeting of the American Association for the Advancement of 
Science Feb. 16 in Denver.

Plants respond to climate change by migrating, evolving and going 
extinct.  However, Wilf notes that due to human activity, global 
change is occurring at breakneck speed today. Because of the 
geologically rapid pace of human-induced extinctions, habitat loss and 
climate changes, land plants currently face a situation more closely 
resembling the K-T than the P-E boundary.

Both the plant and insect studies used three fossil areas for samples; 
the K-T was represented by fossil beds in North Dakota, while the P-E 
was represented by two areas in Wyoming. Reporting on the fossil plant
communities were Wilf; Kirk R. Johnson, curator of paleontology, 
Denver Museum of Nature & Science; and Scott L. Wing, National Museum 
of Natural History, the Smithsonian Institution. In a subsequent 
paper, Wilf, Johnson and Conrad C. Labandeira, National Museum of 
Natural History, the Smithsonian Institution, discussed the role of 
insects in teasing out climate change influences on ecological 
communities.

Fossilized leaves show a record of insect predation not unlike what is 
seen on leaves today. On some leaves, the imprint of piercing and 
sucking insects is visible. Others show the ragged margins or holey 
centers of leaves chewed by hole feeding and margin feeding insects. 
Evidence of mining insects is also preserved, as are galls. The fossil 
record preserves even the totally skeletonized leaves that show only 
veins.

By looking at the damage, the researchers can categorize the types of
insects that infested these forests 65 and 55 million years ago, and 
trace the extinction and evolution of species. Labandeira looked at 
13.5 thousand leaves across the K-T and identified 51 types of insect 
feeding damage. The researchers found that the K-T impact was 
associated with a significant and enduring loss of plant and insect 
species. Among insects, the most affected were the specialized 
feeders, those insects that fed on leaves of only one type of plant.

Insects died both from the impact and because the trees that they fed 
on died. Specialized feeders were less able to adapt and eat off any 
tree available and so were more greatly effected.

"At the K-T boundary, we see the largest spike of the last appearance 
of species, both for plants and insects that ate them," says Wilf. 
"Although climate change was occurring for a long time before the K-T, 
its effects could not hold a candle to the extinctions brought on by 
the impact."

Only 21 percent of species made it across the K-T boundary and only 11
species originate in the Paleocene indicating the recovery was not
immediate. In fact, diverse vegetation does not return in the area 
studied until the warm early Eocene 12 million years after the impact.

"The P-E transition was a relatively long, slow change that allowed 
the plants and insects to adapt to the shifting environment," says 
Wilf. "At the K-T, species could not adapt in time because the change 
was so rapid. These rapid changes were much more like what we have 
today than the gradual ones that occurred at the P-E. Organisms cannot 
migrate in response to climate changes as they did during the Eocene 
because of because of freeways and parking lots, and the ongoing loss 
of habitat imposes severe and geologically sudden stress on 
ecosystems."

                            **aem**

http://www.psu.edu/ur/2003/leafinsects.html

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