Several mass extinctions have occurred throughout Earth's history, the most recent of which was the Permian-Triassic extinction event, also known as the "Great Dying," which occurred 252 million years ago.
While scientists generally agree on the causes, the exact mechanism by which this mass extinction occurred - and the subsequent ecological collapse - remains a mystery.
Researchers examined marine ecosystems before, during, and after the Great Dying in a study published today in Current Biology to better understand the chain of events that led to ecological destabilization.
biodiversity loss drove ecological collapse after the 'Great Dying'
In doing so, the international research team, comprised of scientists from the California Academy of Sciences, the China University of Geosciences (Wuhan), and the University of Bristol, revealed that biodiversity loss may be a precursor to a more devastating ecological collapse, a troubling finding given that the rate of species loss today outpaces that during the "Great Dying."
According to Academy Curator of Geology Peter Roopnarine, PhD, the Permian-Triassic extinction serves as a model for studying biodiversity loss on our planet today.
"In this study, we determined that species loss and ecological collapse occurred in two distinct phases, with the latter occurring about 60,000 years after the initial biodiversity crash," he said, as per ScienceDaily.
The event itself wiped out 95% of Earth's life or roughly 19 of every 20 species.
It caused climatic conditions similar to today's human-caused environmental challenges, such as global warming, ocean acidification, and marine deoxygenation, and was most likely caused by increased volcanic activity and a subsequent spike in atmospheric carbon dioxide.
In order to recreate the ancient marine environment, researchers examined fossils from South China, which was a shallow sea during the Permian-Triassic transition.
The team was able to analyze prey-predator relationships and determine the functions ancient species performed by categorizing species into guilds, or groups of species that exploit resources in similar ways.
These simulated food webs represented the ecosystem before, during, and after the extinction event in a plausible way.
According to Professor Michael Benton of the University of Bristol, the fossil sites in China are ideal for this type of research because we need a lot of fossils to reconstruct food webs.
The rock sequences can also be precisely dated, allowing us to follow a step-by-step timeline of the extinction process and eventual recovery.
When multiple species perform similar functions, an ecosystem as a whole is more resistant to environmental change.
If one species becomes extinct, another can fill the void, and the ecosystem is preserved.
This is analogous to an economy in which multiple companies or corporations provide the same service.
The demise of one corporation does not affect the service or the economy, but it does if the service is monopolized by a single entity.
"We discovered that the first phase of extinction's biodiversity loss was primarily a loss in functional redundancy, leaving a sufficient number of species to perform essential functions," Roopnarine said.
However, when environmental disturbances such as global warming or ocean acidification occurred later on, ecosystems that reinforced resistance were missing, resulting in abrupt ecological collapse.
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What exactly is at stake?
Many elements that ensure the planet's habitability, such as greenhouse gas concentrations, forested areas, and the health of marine ecosystems, have been declining at an accelerating rate since the mid-1950s, negatively affecting ecosystems that are the foundation for human life, as per Global Challenges Foundation.
Ecosystems perform a variety of functions known as environmental services, without which human societies and economies would be unable to function.
We rely on environmental services to provide us with air, water, food and fiber, shelter, and energy.
Ecosystems can tolerate a measure of impact from human use and recover after a period of time with minimal negative effects - an attribute generally known as resilience - but beyond a certain threshold, or "tipping point", sudden and radical disruption can occur, which may lead to "ecosystem collapse".
Soil quality, freshwater supplies, and biodiversity all suffer as a result of these conditions, while agricultural capacity plummets and daily human living conditions deteriorate dramatically.
Despite little research, new evidence on "ecosystem collapse" is emerging as a result of factors such as human pressure and climate change.
Several examples of "ecological collapse" in the past and present have been documented.
The former includes Easter Island, while the latter includes the ecological collapse in and around the Aral Sea, which had dramatic social and economic consequences before recovering gradually.
Another example is the ecological changes observed in and around Lake Chad, which have had a dramatic negative impact on people and the region's ecosystem; diminishing water resources and a decline in the lake's ecosystem have resulted in severe health and economic impacts for the populations surrounding Lake Chad, as well as affecting fishing communities and pastoralists and generating resource-based conflicts.
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