I have no doubt that the evidence shown here is quite correct, but taking the inference as far as done here is pretty chancy on the basis of one fossilized snapshot.. Putting this is a more recent perspective, a few warming winters and I am talking about a couple of degrees, was sufficient to wipe out huge tracts of pine with the pine beetle. It really does not take very much for a shift here and there to act as a force multiplier in a given biome.
That evidence suggests that insect depredation is primarily a function of climatic conditions over decadal timelines. We already know that a single degree produces huge impact on crop placement and from this on insect populations.
The changes 55 millions of years ago were way more dramatic and decisive than anything the Holocene may ever throw at us so a radical change in insect populations was an inevitability then and that changing plant conditions show up in the fossil record is to be expected. It is nice to see it confirmed.
Why CO2 rose dramatically 55 millions of years ago is not well understood at all and it is way premature to attempt to link causes and effects. In fact the heating that took place may have been responsible for the sharp rise in the atmospheric CO2. In fact if we use that as our guide post, then we are left with either a close encounter with a star or with volcanics. The star proposition is already covered off with a known hundred thousand year orbit around Sirius that also shows us that the dwell time for such an event is simply too short for the events 55 millions of years ago.
That pretty well leaves super sized volcanic activity that was able to supply both heat and CO2. scenarios have been suggested and it will be eventually be sorted out.
Fossil Record Suggests Insect Assaults on Foliage May Increase with Warming Globe
June 12, 10:07 AM ·
The following is a press release from the National Science Foundation.
More than 55 million years ago, the Earth experienced a rapid jump in global carbon dioxide levels that raised temperatures across the planet. Now, researchers studying plants from that time have found that the rising temperatures may have boosted the foraging of insects. As modern temperatures continue to rise, the researchers believe the planet could see increasing crop damage and forest devastation.
The researchers, from Penn State, the Smithsonian Institution, the University of Maryland, the University of California, Santa Barbara, and Wesleyan University published their findings in the Feb. 11, 2008, Proceedings of the National Academy of Sciences.
"Our study convincingly shows that there is a link between temperature and insect feeding on leaves," said lead author Ellen Currano of Pennsylvania State University and the Smithsonian Institution. "When temperature increases, the diversity of insect feeding damage on plant species also increases."
With support from the National Science Foundation (NSF), Currano collected the study fossils from the badlands of Wyoming, gathering more than 5,000 fossil leaves from five sites representing time zones before, during and after the roughly 100,000 year temperature spike called the Paleocene-Eocene Thermal Maximum (PETM).
The researchers found that the PETM plants were noticeably more damaged than fossil plants before and after that period. The PETM plants, many of which are legumes -- the family that now includes beans and peas -- show damage with greater frequency, greater variety (such as mining, galling, surface feeding and other assaults) and a more destructive character than plants from the surrounding geologic time periods.
"This study shows that insects responded rapidly to a major change in climate during the PETM," said Enriqueta Barrera, program director in NSF's Division of Earth Sciences, which helped fund the project. "This is in agreement with previous findings by [co-author] Scott Wing of the Smithsonian Institution who found that plants that previously were common much farther south migrated northward at this time"
In order to test alternative reasons for the increased damage, the researchers looked at whether the plants in the analysis had key traits that made them more palatable to insects. However, after using established analytical techniques to measure various leaf structures in all of the specimens, the researchers concluded that the PETM plants do not appear to vary structurally from the plants in the rock layers above and below the temperature spike.
The researchers also looked to see if the insect species feeding on the leaves changed over the time period. The analysis showed that what changed was the abundance of insect species that are highly specialized in the type of plant they consume and the way they consume it, such as leaf miners and gallers - they are far more abundant in the PETM.
"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."
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.
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