Fossil record suggests insect assaults on foliage may increase with warming globe

"We wanted to see whether the increase in insect damage during the PETM was because the leaves were less tough or more nutritious," said Currano. "There is no evidence to support this. Instead, we think that the warming allowed insect species from the tropics, particularly those that feed in a highly specific manner, to migrate north."

During the Paleocene-Eocene Thermal Maximum more than 55 million years ago, insects chewed large holes in this leaf. Click here for more information.

Biologists are already aware that insects in the tropics consume more plants and that warming temperatures are causing organisms to widen their ranges. In addition, research has shown that plants grown under higher concentrations of carbon dioxide (CO2) are less nutritious, so insects must eat more plant tissue to get the same sustenance. These earlier studies support the recent findings about the PETM.

Because food webs that involve plant-eating insects affect as much as three quarters of organisms on Earth, the researchers believe that the current increase in temperature could have a profound impact on present ecosystems, and potentially to crops, if the pattern holds true in modern times.

"This study represents a highly integrative approach, using well-studied systems, to model ecological dynamics during upcoming climate shifts," said William Hahn, a program director in NSF's Division of Graduate Education who supported Currano's work with a research fellowship. "The truly relevant description of past climate-change effects on plant-insect interactions, specifically the probability of increased insect damage to plants with rising temperatures, is a forward-looking approach that will help us prepare for the effects of future global warming," he added.

In addition to Currano's Graduate Research Fellowship, the research team was supported by grants from NSF's Division of Earth Sciences, as well as funding from the Roland Brown Fund of the Smithsonian's National Museum of Natural History, the Evolving Earth Foundation, the Paleontological Society, Penn State, the Petroleum Research Fund, the David and Lucile Packard Foundation and the University of Pennsylvania.