The PETM occurred 55.8 million years ago and was an abrupt global warming event linked to a temporary increase in carbon dioxide in the atmosphere. This event is comparable in size and rate to the current climate changes brought on by human activity.
"Our study suggests that increased insect herbivory is likely to be a net, long-term effect of anthropogenic carbon dioxide increase and warming temperature," the researchers report today (Feb.11) in the online Proceedings of the National Academy of Sciences.
Today, the tropics have the most diverse insect populations and the highest rate of herbivore damage on leaves. This implies that there is a correlation between insect feeding and temperature. The researchers, who include Ellen D. Currano, graduate student in geoscience, and Peter Wilf, associate professor of geoscience, Penn State; Scott L. Wing and Conrad C. Labandeira, Department of Paleobiology, Smithsonian Institution; Elizabeth C. Lovelock, graduate student in earth science, University of California, Santa Barbara; and Dana L. Royer, assistant professor, earth and environmental sciences, Wesleyan University, looked at fossil leaves from the Bighorn Basin in north central Wyoming from layers deposited in the late Paleocene, in the middle of the PETM and in the early Eocene.
"We looked at these time periods to see evidence of insect feeding and to count the types of damage," says Currano. "We looked to see how much damage the insects did and the kinds of leaves on which the damage occurred."
They identified 50 types of damage on the fossil leaves including holes of varying sizes, chewed-out areas, galls and mines.
"We can identify certain insect groups by the way they feed on a leaf," says Currano. "Some make mines while others chew along the edge of the leaf."
By looking at modern insect's behavior, the researchers can determine the types of insects eating the fossil leaves. They compare modern leaf damage to that occurring in the past.
The team found that the percent of leaves damaged by insects was 15 to 38 percent during the Paleocene and 33 percent during the Eocene, but increased to 57 percent during the intermediate PETM. This large increase in insect herbivory corresponded to a time of increased carbon dioxide and temperatures. The researchers also found that the increased feeding occurred in all plant species and that a more diverse array of insects fed on the leaves.
The researchers investigated the leaves that grew during the PETM to ensure that the leaves growing then were not tougher and less tasty than those found before or after that period. They found no differences between the heavily eaten leaves and those from time periods with less herbivory.
"With more carbon dioxide available to plants, photosynthesis is easier and plants can make the same amount of food for themselves without having to put so much protein in their leaves," says Currano.
Consequently, when carbon dioxide increases, leaves have less protein and insects need to eat more to acquire the nutrients they need. While increased carbon dioxide is good for the plants in that they can increase growth, plants also suffer from increased feeding by insects.
The researchers explain that the increase in insect feeding is a result of the tripling of carbon dioxide in the atmosphere during the PETM and the accompanying rise in temperature. They think that increases in temperature and carbon dioxide levels during the PETM are good analogs for the future and therefore, that plants may eventually experience higher rates of feeding as humans put more carbon dioxide into the atmosphere.
Andrea Elyse Messer | EurekAlert!
Safeguarding sustainability through forest certification mapping
27.06.2017 | International Institute for Applied Systems Analysis (IIASA)
Dune ecosystem modelling
26.06.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau
3-D shape acquisition using water displacement as the shape sensor for the reconstruction of complex objects
A global team of computer scientists and engineers have developed an innovative technique that more completely reconstructs challenging 3D objects. An ancient...
Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.
For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...
What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.
To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...
The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....
A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...
21.07.2017 | Event News
19.07.2017 | Event News
12.07.2017 | Event News
24.07.2017 | Power and Electrical Engineering
24.07.2017 | Materials Sciences
24.07.2017 | Materials Sciences