Lack of Spare Species Leaves Ecosystems Flat


Having back-up plans and built-in redundancy features can save lives, whether it’s emergency flares in the trunk of the car or warning lights and alarms in the cockpit of an airplane. For Earth, failures in redundancy can lead to catastrophe.

In nature, multiple species compete for the same resources, something called ecological redundancy. For example, several species of sharks may feed on the same prey fish. If one species disappeared, the other sharks would take up the slack on chowing down on the extra fish – keeping the system in balance. But if multiple species of shark go extinct, a situation that is currently playing out, the system can veer toward collapse.

For the first time researchers have made a direct connection between loss of redundancy and ecosystem collapse. Their work, published recently in the journal Geology, shows that during extinction events in the Permian and Triassic periods, the Earth’s ancient oceans lost critical back-up species.

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The research holds a dire warning about humans activities in the oceans and points out the importance of preserving whole ecosystems, not just individual species.

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“It’s definitely a cautionary tale because we know it’s happened at least twice before,” said Jessica Whiteside of Brown University, the paper’s lead author in a press release. “And you have long periods of time before you have reestablishment of ecological redundancy.” In these cases, it took 10 million years for nature to balance itself out again, the team reported.

Many marine biologists worry that fisheries worldwide are in collapse. Overfishing of predatory species, like bluefin tuna, sharks, and swordfish has eliminated, not just competing species, but entire levels of the food chain.

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“It is difficult to evaluate what is going on at present, given that we don’t have the advantage of the long lens of geologic history, where we can see things play out over millions of years,” Whiteside wrote in an email to Discovery News. “But there is evidence that trophic (i.e. food-web) collapse is starting to occur in some marine ecosystems.”

One example of ecosystem collapse in the modern world can be seen off the coast of North Carolina, Whiteside said. The disappearance of the blacktip shark allowed the cownose ray population to explode. This event, called a trophic cascade, collapsed the area’s century-old bay scallop industry.

Similar situations occurred 250 and 200 million years ago. Predators similar to the modern day nautilus, called ammonites, were once common and diverse. But many species went extinct after massive volcanic eruptions in the Permian and Triassic caused devastation and atmospheric disruption. The resulting climate change reduced ammonites to only a few species.

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The result was a simplified food chain. A few hardy species survived the extinctions and became common. Generalist species expanded and filled wide ranges of the food web, as opposed to locally adapted species filling specific niches. Other research has suggested that homogeneous populations of generalist species can actually slow the divergence of new species and subsequently the ecosystem’s recovery.

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After the ancient extinctions, biodiversity and robust ecosystems slowly re-emerged. To understand this re-emergence, the ammonite researchers analyzed carbon isotopes in the fossils. The scientists were then able to measure the stability of the carbon cycle in the ancient oceans.

Disruptions, like the volcanic events of the Permian and Triassic, caused species numbers to plummet. After disturbances, it took up to 10 million years for fluctuations to settle down and a stable pattern to develop. Highest species diversities of ammonites were found when the carbon isotope values were stable.

“The take home message is that biodiversity matters,” Whiteside told Discovery News. Not just because it’s nice to look at a bunch of species, she said, but because ecosystem functioning is reduced by biodiversity loss.

IMAGE: Artist’s conception of an ammonite; Wikimedia Commons


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