Spurring species: Predation intensity (as illustrated by benthic marine invertebrates with predatory drillholes and repair scars) and global biodiversity (white line) were tightly correlated over the last 540 million years.
Credit: Finnegan Marsh/James H. Nebelsick.
SYDNEY: A strong link has been found in the fossil record between the intensity of predation and the diversity and number of animal species over time.
It is not clear whether one factor caused the other or a third underlies both – but experts argue that it's one of the first examples of a direct link between ecological interactions and large-scale evolutionary patterns.
The study – which probes 540 million years of animal evolution – is detailed this week in the U.S. journal, the Proceedings of the National Academy of Sciences.
There has been intense debate among palaeontologists about the degree to which ecological interactions have contributed to evolution.
According to one hypothesis, ecosystems have become progressively more dangerous over the last 500 million years. This has directly impacted animal evolution – leading to the evolution of shells, tough carapaces and other defensive structures.
Drill holes and repair scars
In order to answer the question of whether ecological interactions matter over massive timescales, John Warren Huntley and Michal Kowalewski, from Virginia Polytechnic Institute in Blacksburg, U.S., scoured the fossil record for the tell-tale damage of predation.
They particularly searched for predator 'drill holes' and repair scars in the shells of marine invertebrates – which are evidence of attempts to attack them. Simultaneously they recorded species diversity in the entire fossil record over the last 540 million years.
The pair discovered that predation increased notably around 480 million years ago, some 70 million years earlier than previously supposed. Moreover, predation intensity and biodiversity of marine creatures continued to be tightly linked throughout the entire time span examined.
"Our job now is to determine what this correlation means," said Huntley. "Did change in predation intensity drive change in diversity? Did change in diversity drive change in predation intensity? Or were patterns in both predation intensity and diversity driven by a separate factor?"
Joshua Madin from the National Centre for Ecological Analysis and Synthesis, at the University of California in Santa Barbara, believes the work requires careful interpretation. "Information captured in the fossil record is very patchy. This means that we need to be very careful when making conclusions about these relationships."
However, "despite large gaps and significant noise" the study is good step to helping us better understand how large-scale ecological and evolutionary trends are linked, he said.
