Predator-prey encounters fuelled diversity of marine creatures

Virginia Tech geoscientists have reported in the Proceedings of the National Academy of Sciences that the diversity of marine creatures increased and decreased over hundreds of millions of years in step with predator-prey encounters.

Washington, Sept 11 : Virginia Tech geoscientists have reported in the Proceedings of the National Academy of Sciences that the diversity of marine creatures increased and decreased over hundreds of millions of years in step with predator-prey encounters.

For decades, scientists have debated on the role of ecological interactions, such as predation, in the long-term patterns of animal evolution.

As part of their study, post-doctoral scientist John Warren Huntley, and Geosciences Professor Micha Kowalewski decided look at the importance of ecology by surveying the literature for incidents of predation in marine invertebrates, such as clams and their relatives.

The researchers also looked for repair scars on the shells of creatures that survived an attack.

"Today, certain predators leave easy to identify marks on the shells of their prey, such as clean, round holes. Such holes drilled by predators can also be found in fossil shells," said Huntley.

Findings revealed that predation increased notably about 480 million years ago, some 50 million years earlier than what previous studies have found.

However, the most notable discovery was the observation that the incidence of drill holes and repair scars were strikingly parallel to Sepkoski's diversity curve for marine invertebrates.

This diversity curve, compiled by the late Jack Sepkoski of the University of Chicago, records the origination and extinction of marine animal genera through the last 540 million years (Phanerozoic).

"There is a strong correlation between predation intensity and global marine biodiversity in the Phanerozoic," Huntley said.

In their article, "Strong Coupling of Predation Intensity and Diversity in the Phanerozoic Fossil Record," Huntley and Prof. Kowalewski now offer three rival hypotheses to explain the correlation.

"It's the classic problem with interpreting a correlation. You have to be careful when ascribing a cause. Let's say factors X and Y are correlated. A change in X could cause a change in Y, a change in Y could cause a change in X, or X and Y could both be controlled by another factor," said Huntley.

According to Huntley, the first hypothesis is that predation intensity could be driving diversity.

"In this case, ecological interactions would matter in evolution. Organisms evolve over the long term in response to their enemies, and with increased predation intensity more species evolve," said Huntley.

The second hypothesis, Huntley said, is that as biodiversity increased, by chance predators with more complex feeding strategies evolved.

"Predatory techniques like drilling and peeling shells are more evolutionarily-derived than more primitive forms of predation like whole ingestion. In this scenario you would expect to evolve sophisticated forms of predation only when diversity is high," said Huntley.

"And the third hypothesis is that something else is driving both predation and biodiversity," he said.

"Some periods have more sedimentary rocks, and therefore more fossils, preserved than others. There is less diversity to be observed when there are fewer fossils to study," Huntley added.

ANI