Study headed by UH Hilo evolutionary ecologist shows surprising findings about animal diversity and extinction
In a collaborative study led by Matthew Knope, findings show animal biodiversity in modern oceans is best explained by lower extinction rates in animal groups that are ecologically diverse, rather than by higher origination rates, as previously predicted.
A collaborative study on animal biodiversity led by the biology department at the University of Hawai‘i at Hilo is published in the Feb. 28, 2020, issue of the journal Science. The study shows that animal biodiversity in the modern oceans is best explained by lower extinction rates in animal groups that are ecologically diverse, rather than by higher origination rates (rates at which the number of species increases), as previously predicted.
Matthew Knope, assistant professor of biology and evolutionary ecologist, is lead author of the study, “Ecologically diverse clades dominate the oceans via extinction resistance.” Co-authors are Andrew Bush from University of Connecticut, Luke Frishkoff from the University of Texas at Arlington, Noel Heim from Tufts University, and Jonathan Payne from Stanford University.
After publication of this story, Knope tweets, “This study is a life-long dream fulfilled. Working with this group of co-authors was a highlight of my career.”
This study is a life-long dream fulfilled. “Ecologically diverse clades dominate the oceans via extinction resistance” @ScienceMagazine. Working with this group of co-authors was a highlight of my career. Please R/T to share broadly.https://t.co/P6qtOt2SD2
— Knope Evolutionary Ecology Lab (@LabKnope) February 28, 2020
The study examines approximately 20,000 genera of fossil marine animals across the past 500 million years, and approximately 30,000 genera of living marine animals.
Ecological differentiation is correlated with taxonomic diversity in many clades, and ecological divergence is often assumed to be a cause and/or consequence of high speciation rate. However, an analysis of 30,074 genera of living marine animals and 19,992 genera of fossil marine animals indicates that greater ecological differentiation in the modern oceans is actually associated with lower rates of origination over evolutionary time. Ecologically differentiated clades became taxonomically diverse over time because they were better buffered against extinction, particularly during mass extinctions, which primarily affected genus-rich, ecologically homogeneous clades. The relationship between ecological differentiation and taxonomic richness was weak early in the evolution of animals but has strengthened over geological time as successive extinction events reshaped the marine fauna.
“Animals in the oceans today are more diverse than they have ever been in the history of life on Earth and scientists have long worked to describe how they have come to be that way,” says Knope. “Our findings clearly show that the most ecologically diverse animal groups are also the most dominate animals in terms of numbers of genera in the modern oceans.”
Knope says animals that are members of ecologically flexible groups are resistant to extinction, particularly during mass extinctions that primarily impacted ecologically homogeneous groups.
“The oceans we see today are filled with a dizzying array of species in groups like fishes, arthropods, and mollusks, not because they had higher origination rates than groups that are less common, but because they had lower extinction rates over very long intervals of time,” Knope explains.
“Perhaps the fable of the tortoise and the hare is apt in explaining marine animal diversification,” he says. “Some groups jumped out to an early diversity lead only to be surpassed by other groups that were more ecologically diverse and less evolutionarily volatile, with steady diversification rates and strong resistance to mass extinctions.”
Rosemary Gillespie, professor of evolutionary biology at the University of California, Berkeley, who was not involved in the study, explains that understanding how biodiversity is structured, both in space and time, has always been a major focus in biology. But the research is difficult because current patterns of biodiversity are dictated both by origination and extinction; researchers can infer origination rates through examination of extant biodiversity, but elucidating the role of extinction is notoriously difficult.
“This [Knope, et al.] study represents some of the most detailed and careful analyses of the fossil record to date, showing very clearly the importance of the slow and steady development of lineages through time has been a key factor in dictating which lineages have achieved the highest diversity,” says Gillespie.
Michal Kowalewski, professor of invertebrate paleontology at the University of Florida, who also was not involved with the study, says Knope and colleagues, in their analysis of massive data derived from the fossil record, directly address one of the critical questions of biology: Why do certain types of animals occupy exceptionally broad spectra of ecological niches?
“As importantly, the study highlights the truly unique value of paleontological data for assessing core questions of biology and exploring historical roots of the modern biosphere,” Kowalewski says.
Matthew Knope, evolutionary ecologist
Assistant Professor Knope arrived at UH Hilo in the fall of 2016. He is an evolutionary ecologist specializing in speciation and extinction, specifically the generation and loss of plant and animal biodiversity in Hawai‘i and globally, working on research questions that lie directly at the intersection of ecology and evolution. One of the main goals of Knope’s research program is integrating the way biologists study living organisms with the way fossil organisms are studied, so that direct comparisons can be made between the modern and the ancient.
A significant contribution to the literature is Knope’s study that showed, for the very first time, the basic ecological differentiation history of animals in the oceans across all time. See Limited role of functional differentiation in early diversification of animals (Knope, et. al., Nature Communications, March 4, 2015).
“We expected to see most of the basic ecological strategies show up very early in the evolution of animal life in a quick burst, but we found just the opposite, that it has taken about 500 million years to slowly accumulate new ecological strategies with strong upticks in the 10-20 million years after mass extinctions,” Knope, lead author of the study, explains in an email.
“What we show is that marine animals have followed a ‘late filling’ model in which it has taken the past 542 million years to get to where we are now—a world filled with a dizzying array of animals doing vastly different things from one another. The world that we see today has really been formed over the very long expanse of evolutionary time.”
To learn more about the study, see Animal functional diversity started out poor, became richer over time (Stanford University, March 4, 2015), and watch video below.
Learn more about Knope’s teaching and research at the Knope Evolutionary Ecology Laboratory website.
UH Hilo ecologists identify groups of species at greatest risk of extinction
Story by Susan Enright, a public information specialist for the Office of the Chancellor and editor of UH Hilo Stories. She received her bachelor of arts in English and certificate in women’s studies from UH Hilo.
Update: In the News
Ability to Take on Diverse Roles May Be Key to Which Animals Survive Mass Extinction, Scientific American, Feb. 28, 2020.