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Global population trends among 71,000 animal species show nearly half are “sliding toward extinction,” some at alarming rates, a new study warns.
Researchers found 48% of the species in the analysis were declining, while only 3% were increasing and 49% remain stable, according to the study published Tuesday in the journal “Biological Reviews.”
The disparity between the declining number of species and the increasing number shows “a net loss of biodiversity that is quite alarming,” said Daniel Pincheira-Donoso, a study co-author and an associate professor in evolutionary biology and macroecology at Queen’s University Belfast in the United Kingdom.
The rapidly increasing imbalance signals a looming “sixth extinction,” the authors stated in the study, titled: “More losers than winners: investigating Anthropocene defaunation through the diversity of population trends.”
Although the declining species are cause for concern, Stuart Pimm, a conservation scientist for nearly 50 years who is not associated with the study, said its other findings represent good news for many species.
The study “gets past the simplistic view that everything is going to hell,” said Pimm, Doris Duke Chair of Conservation Ecology at Duke University. “Many species — and many important species — and doing OK, or even better.”
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What were the study’s findings?
Population trends were analyzed in the world’s mammals, birds, reptiles, amphibians, fish, and insects. The study found “animal populations and whole species are declining across the tree of life.”
Among its other findings:
- Biodiversity is under increasing threat from habitat destruction, invasive species, and other factors.
- The scale of decline among the animals represents “one of the most alarming consequences” of the human impacts on the planet.
- The number of populations collapsing “is far higher than the species adaptively ‘catching up’.”
- Population trends are unknown for large numbers of species, particularly in the tropics where other species are in trouble.
- Reptiles and fishes have more stable groups than some other species, but they also have a larger number of species where the population trends are unknown.
- Amphibians are undergoing some of the greatest decreases in population losses, with 63% of the species examined decreasing.
- Of the species classified by the International Union for Conservation of Nature’s red list as “non-threatened,” 33% are declining.
“Now is the pivotal time to protect the future integrity of biodiversity, and thereby the persistence of humanity,” the authors concluded.
Not all bad news
The study’s findings are “interestingly and importantly mixed,” said Pimm, in Africa studying elephants this summer.
“Some species are in deep trouble, but we ought not to forget that we are making a lot of successes with a lot of endangered species,” he said. “There are some places where things are really pretty grim, but others where things are an awful lot better.”
“If you’re a skylark, an iconic bird of the English countryside, you’re in trouble,” because of intensive agriculture, insecticides, and herbicides, Pimm said. But success stories are found among elephants in southern Africa, and bald eagles, peregrine falcons, and many ducks in the U.S.
“A lot of things are going better because we made it that way,” and the success illustrates further strides can be made, he said. He pointed for example to the United Nation’s goal of conserving 30% of the world’s land and oceans by 2030.
Why should we care about vanishing species?
It’s an “environmental global catastrophe” that will sooner or later impact our own lives, said Pincheira-Donoso. He compared the importance of biodiversity to a car’s engine.
“An engine is made of very big critical bits and very small bits like screws, but all of those elements are in that engine because together they make the engine work,” he said. “If you start taking small bits from it, or certainly if you take a big bit, you know your engine will fail and will end up collapsing.”
The same complex interaction happens in natural ecosystems, he said. “If you start removing species from an ecosystem, it’s the equivalent to removing screws from random bits of your engine, you know it’s going to collapse because every species plays a role.”
Amphibians, for example, play large roles in ecosystems, but they are declining more than any other living organisms, said Pincheira-Donosa.
“The rate of extinction of amphibians is truly alarming … more than all the other vertebrates combined,” he said. “In every ecosystem where you see a massive decline of amphibians, you are basically taking a lot of random screws from your engine and that is causing a collapse.”
What were the five mass extinctions?
Using the fossil record, scientists have found five periods in Earth’s geological history when many species died. According to the American Museum of Natural History, the periods and the extinctions were:
- Ordovician-silurian: 440 million years ago. Small marine organisms.
- Devonian: 365 million years ago. Many tropical marine species.
- Permian-triassic: 250 million years ago. A range of species, including many vertebrates.
- Triassic-jurassic: 210 million years ago. Vertebrate species on land.
- Cretaceous-tertiary Extinction: 65 million years ago. An estimated 50% of Earth’s plants and animals.
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