Applying an algorithm similar to the one Facebook uses to make friend suggestions, the researchers identified communities of ancient life in the fossil record and tracked their numbers through each of the planet’s mass extinctions.
As expected, the number of communities – a group of different species living in the same general area – dropped during mass extinction events. But the rate at which communities disappeared did not always keep pace with the overall loss of life and biodiversity during an extinction, a result which suggests that the ecological impacts of an extinction are not always related to the number of perishing species.
“There have been times in our history when there have been major events that have seen huge changes in communities, but very few species have gone extinct,” said lead author Drew Muscente, who has conducted the study when he was a postdoctoral researcher at the University of Texas at Jackson School of Geosciences in Austin. “And there have been events where many species have gone extinct and communities and ecosystems have been barely affected.”
Muscente is now an assistant professor at Cornell College. The study has just been published in the journal Geology.
The results underscore the importance of studying communities to gain a broader perspective on environmental change – both in the past and in the present.
“We’re trying to understand how changes in these communities lead to a fundamental transformation of entire ecosystems,” said co-author Rowan Martindale, associate professor at The Jackson School.
Identifying communities in the fossil record is notoriously difficult. Most research on paleocommunities focuses on comparing samples and collections of fossils taken from rocks of varying ages and locations. And while conventional computational methods can be used to group samples into paleocommunities, they work best with relatively small datasets of only a few hundred or thousands of fossil collections. Because of this limitation, conventional methods can only be applied to data from specific regions and time periods, as opposed to the full record.
The researchers were able to overcome these challenges and examine the entire fossil record by applying a community detection algorithm based on network analysis methods. Social media companies are known to use these types of methods to connect users, but they are increasingly being applied across a range of scientific disciplines.
According to Muscente, this study is the first time that network analysis has been applied to detect paleocommunities in the entire fossil record of marine animal life – from the appearance of animal life to the current geological era. .
Matthew Clapham, a professor of paleobiology at the University of California, Santa Cruz who was not involved in the study, said another advantage of the network analysis method is the emphasis on visualizing connections, rather than the types of animals present in an ecosystem.
“It brings the analysis closer to how communities actually functioned, because communities and species interactions are networks,” he said.
Drawing on a database of 124,605 collections of marine animal fossils from around the world and representing 25,749 groups or genera of living and extinct animals, the algorithm identified more than 47 million links between these samples and organized them into 3,937 distinct paleocommunities.
The study tracked communities and biodiversity over the past 541 million years. Research has shown that while mass extinction events impacted both, the degree of decline was sometimes different.
Some extinctions have affected communities more than biodiversity. Some have affected biodiversity more than communities. And some affected both pretty much the same way.
Additionally, the researchers did not find a link between the cause of an extinction and whether it had a significant impact on communities or biodiversity.
The results indicate that the larger ecological impacts of extinction relate more to the species lost than to the number of species lost. If key players in an environment are preserved, communities can remain intact. But if too many of these players are removed, the community crumbles with it.
Muscente said he hopes the network analysis methods first applied in this study can be improved and used to study modern ecosystems.
“I would like to try to bridge the gap between the rock record and the present,” he said.
Other study co-authors include scientists from Rensselaer Polytechnic Institute, the University of Idaho, the Carnegie Institution for Science and Harvard University.
The research was funded by the Keck Foundation, the Deep Carbon Observatory, the Alfred P. Sloan Foundation, the Carnegie Institution for Science and the National Science Foundation.