"The K-T caused major extinction among North American plants and insects. The Western Interior U.S. was a dead zone for plants and plant-insect food webs," said Dr. Peter Wilf, assistant professor of geosciences and the David and Lucile Packard Fellow. "We know that right after the extinction, for 800,000 years, there was very low insect predation and plant diversity. We know that 9 million years afterwards, there was renewed diversity in both plants and insects. What happened in the 8 million years in between?
"In modern forests, insect diversity tracks plant populations. If there are few plants, there are few insects, and that is what we expected to see and mostly found throughout the 10-million-year Paleocene. However, we looked extremely hard to test this conventional wisdom and found some shocking exceptions that have given us new ideas about how food webs recover from mass extinction," he added.
The researchers include Wilf; Conrad C. Labandeira, curator, fossil arthropods, the Smithsonian Institution; and Kirk R. Johnson, vice president for research and collections, and Beth Ellis, paleobotany researcher, Department of Earth Sciences, Denver Museum of Nature and Science. They reported their findings in today's (Aug. 25) issue of Science.
The researchers analyzed insect-feeding damage on 14,999 fossil leaves from flowering plants found at 14 sites, 4 from latest Cretaceous, 9 from early and late Paleocene and 1 from early Eocene rocks in Wyoming, Colorado, Montana and North Dakota. Insects eat leaves in many different ways, including chewing, mining, galling, and piercing and sucking; their diverse feeding marks preserve well in the rock record, often when insect body fossils are absent, and give researchers a proxy for both plant and insect diversity from the same fossils.
The majority of the samples followed expectations: the Cretaceous sites were rich in plants and insect-feeding diversity, and the latest Paleocene and Eocene sites showed signs of recovery. Through most of the intervening Paleocene, most floras have low richness of plants and insect damage. Typical numbers of species of plants in the Paleocene range between 15 and 20 at the sites, with many of the same species found throughout the Paleocene. Insect predation was low as well.
In sharp contrast, the team also found two unusual early Paleocene sites. The first, a previously identified site in the Denver basin, in the town of Castle Rock, showed great plant diversity, especially when compared with the other Paleocene floras.
The researchers found nearly 200 different species with thick leaves and drip tips, indicating a tropical rainforest completely unlike the other Paleocene floras. This site was on the eastern slope of the Paleocene Front Range, and Johnson and Ellis' work, as well as recent paleoclimate modeling simulations, has suggested that the local geography allowed high rainfall. While this site shows many different plant species 1.7 million years after the K-T extinction, predation by insects, as seen in preserved mines and galls on the fossil leaves unexpectedly was as low as in other Paleocene sites.
The second site, known as Mexican Hat, in southeastern Montana was even more intriguing.
"We looked at more than 2,000 specimens at Mexican Hat and found the usual 16 species of plants," said Wilf. "But the insect mines were unlike anywhere else in North America."
The researchers found heavy and diverse insect damage; all abundant species were mined, and the four major species each showed more than one kind of mining.
"The mines show great abundance and taxonomic breadth," said Wilf. "There are fly, wasp and moth mines on the sycamores. We have not seen this kind of saturation of a flora with insect feeding anywhere else in North America, even in the Cretaceous before the extinction."
What made this happen at Mexican Hat? The researchers do not know because to date, it is the only example of high insect-feeding diversity on a Paleocene flora. The heavy insect population did not apparently spread from Mexican Hat and perpetuate through time because the same plants at younger sites do not have the feeding associations seen at Mexican Hat.
Wilf suggests that the K-T extinction destroyed the ecological links in the food web. Plants and insects were killed outright, and herbivorous insects took a further hit when the plants they were specialized to eat disappeared. Surviving insects faced the choice of shifting their food resource or dying. Many died, but in most places a few survived, and from these, some evolved to feed on new host plants.
As the ecosystem rebuilt new links from its shattered state, the empty ecological space was open to opportunism, and in a few places the food chain became unbalanced and unstable. At Castle Rock, plants flourished in the warm wet climate and without insect predatory pressure -- possibly because their rainforest-type leaves were already thick, tough, and hard to eat -- plant species proliferated and thrived for a short time. At Mexican Hat, 16 species of mostly thin-leaved, poorly defended, typical Paleocene plants temporarily became the hosts to diverse swarms of insects that then disappeared.
This decoupling of producer and consumer diversity after mass extinction is a new pattern for the fossil record that researchers can now test for its generality.
"Temporally and geographically isolated occurrences of severely unbalanced food webs may be a widespread feature of ecological recovery from mass extinction, resulting from instability, incumbency and opportunism in drastically simplified ecological landscapes," say the authors.
A'ndrea Elyse Messer | EurekAlert!
A new indicator for marine ecosystem changes: the diatom/dinoflagellate index
21.08.2017 | Leibniz-Institut für Ostseeforschung Warnemünde
Value from wastewater
16.08.2017 | Hochschule Landshut
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
23.08.2017 | Life Sciences
23.08.2017 | Life Sciences
23.08.2017 | Physics and Astronomy