“Global Diversity Curves Are Misleading” – Ocean Biodiversity Has Not Increased Substantially for Hundreds of Millions of Years
A new way of looking at marine evolution over the past 540 million years has shown that levels of biodiversity in our oceans have remained fairly constant, rather than increasing continuously over the last 200 million years, as scientists previously thought.
A team led by researchers from the School of Geography, Earth and Environmental Sciences at the University of Birmingham have used a big data approach to study this question, which has been disputed by palaeobiologists in recent years.
Using fossil data collected over the past two centuries, and compiled by hundreds of researchers in the Paleobiology Database over the last 20 years, the team was able to show regional-scale patterns of diversity across geological time from the so-called Cambrian Explosion — the point at which most major groups of animals started to appear in the fossil record — to the present day. Their results were published on April 24, 2020, in Science.
Dr. Roger Close, who led the research, explains: “Studies of marine animal diversity over the last five-hundred-odd million years have historically focussed on estimating how “global” diversity changed through time. The problem is that the fossil record is not really global, because both the amount and the parts of the world that are actually preserved in the fossil record changes so much through geological time. This means that so-called “global” diversity curves are misleading.”
“To get around this problem, we studied diversity at regional spatial scales. This meant that we could focus on places and times that are well-known in the fossil record. By comparing geographic regions that were similar in size, we could show how marine animal diversity varied across both time and space.”
Using these estimates for specific geographic regions, the team was also able to estimate the influence of other environmental factors, such as coral reef systems. At this more localized level, it’s possible to see significant variations in diversity across the globe within time intervals, perhaps in response to environmental differences.
“We think of reefs today as being hotspots of diversity, responsible for housing a disproportionate amount of animal species,” says Dr. Close. “So in areas where there are a higher proportion of reefs, diversity will inevitably be higher.”
“Importantly, though we don’t find any evidence that diversity increased in a continuous, sustained way through long intervals of geological time. This is a major departure from previous studies of “global” diversity. These studies concluded that marine animal biodiversity had increased steadily over the last 200 million years, culminating in modern levels that were greater than any point in Earth’s history. In contrast, our work suggests that modern levels of biodiversity — at least at the regional scales we studied — are not exceptional.”