An ancient global warming lasting 3 million years triggered an onslaught of insect attacks on plants, according to a report in today's Science . Experts laud the study, based on thousands of fossils of nibbled leaves, for its groundbreaking reconstruction of past ecological relationships. But they stress that the changes that took place over such a long period cannot be directly compared to effects of any rapid global warming occurring today.
Biologists who study the impacts of climate change on organisms typically compare field plots staked out at warmer and cooler latitudes. Because plants in the tropics get chomped by bugs more than do plants in temperate latitudes, scientists guessed that warmer climates might promote insect attacks. To see whether the relationship holds true regardless of latitude, paleobotanist Peter Wilf of the Smithsonian Institution in Washington, D.C., looked at the fossil record.
Wilf and the Smithsonian's Conrad Labandeira examined nearly 10,000 leaves from the rich fossil beds of southwestern Wyoming. About half the specimens came from the late Paleocene, 56 million years ago when the region was humid and temperate, much like coastal North Carolina is today. The other fossils came from a period 3 million years later--the early Eocene--after the region had warmed about 7°C to a subtropical balminess similar to that of the Florida Keys.
The remarkably preserved leaves, belonging to 88 species, revealed 41 kinds of insect damage, from munched margins to serpentine mining. The researchers were able to attribute different kinds of damage to distinct feeding strategies and thus could determine that plants from the warmer Eocene were attacked up to 20% more often and by a greater diversity of species than their Paleocene predecessors.
"One of the nicest things about the study is that it uses the fossil record to address theories that have only previously been tested using modern-state communities," says Phyllis Coley, a tropical ecologist at the University of Utah, Salt Lake City. Tropical biologist Margaret Lowman at Selby Botanical Gardens in Sarasota, Florida, adds that the work is notable because ecologists are always looking for ways to study long-term interactions among species. "To have such an enormous time span," she says, "is quite innovative and exciting."