Imagine looking up at a sky so full of birds that they block out the sunlight. Carrier pigeons (Migratory Ectopists) used to fly in flocks of hundreds of millions or even billions of birds that took hours to pass overhead. Then we started shooting at them.
Humans began commercially hunting homing pigeons in the 19th century, and by 1914 they were extinct, according to Audubon magazine. These birds are a prime example of how quickly and efficiently humans can wipe out even the most common species. But is it just us, or can nonhuman animals drive other animals to extinction?
Sort of, but humans are usually involved. Some animals are capable of interspecific decimation if humans place them in the wrong place and they become invasive — species that cause ecological or economic damage to their non-native environment. For example, Burmese pythons (Python bivittatus) from Asia gobble up everything that moves in Florida Everglades. The python population started as freed and escaped pets, according to Florida Museum of Natural History.
Species that cannot recognize or respond appropriately to a new species in their environment are called “naive”, or suffer from ecological naivety. It’s not their fault; animals no to evolve Flee or defend against aliens in the blink of an eye, and adaptations don’t just happen overnight.
“The main way aliens wipe out natives is through consumption – so introduced predators into areas where there were no predators before, or the types of predators there were different,” Tim Blackburn , professor of invasion biology at University College London in the UK, told Live Science. “It gives them a sort of intrinsic advantage that allows them to smash their way through naive faunas. [animals of a particular region].”
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Blackburn’s example of an invasive species is the domestic cat. “They contributed to the extinction of dozens of bird species,” he said – the Stephens Island Wren (Traversia lyalli) in New Zealand, which disappeared in 1895, is an example. Cats are the leading direct human cause of bird mortality in the United States and Canada, according to the American Conservatory of Birds. In other words, American birds are more threatened by house cats than by firearms.
Humans are responsible for moving cat hunters and giant snakes around the planet. Everything they do next will be up to us. But what about when animals naturally migrate to a new area? According to Blackburn, animals tend to disperse naturally into neighboring areas, where species types are generally similar and therefore react appropriately to each other – so there are usually no unfair confrontations. .
Sometimes the movement of the earth forces an interspecific upheaval. The Great American Biotic Exchange (about 10 million to 10,000 years ago) is a striking example of this; tectonic plates pushed North and South America together, and species from each continent met via a Central American land bridge. South America was introduced to many new animals, including predators such as bear and big cats, while North America received species like sloth on the ground and relatives of armadillos called glyptodonts in return.
The diversity of animals that moved from North America to South America was higher than vice versa, so South America gained more new residents. A 2020 study published in the journal Proceedings of the National Academy of Sciences proposed that this was due to a disproportionately higher rate of extinction of South American mammals. In other words, more species from South America disappeared during the exchange and fewer were able to colonize North America.
“Perhaps native South American mammals were more susceptible to novel predators,” said Juan Carrillo, a paleobiologist at the University of Friborg in Switzerland and lead author of the 2020 paper. Carnivore Predation North Americans is just one hypothesis for what drove the asymmetric exchange.
“Ground sloths and glyptodonts were probably large enough to escape these predators,” Carrillo told Live Science. “And that may be one of the reasons why they were able to migrate north and we found them in the fossil record of many parts of North America.”
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But while the impact of modern invasive species on extinctions is clear, the exchange paints a more complicated picture. “It wasn’t just a moment in the Earth history, but actually spanned millions of years and went through different phases,” Carrillo said. The South American extinctions took place during a period of climate change when the Earth was cooling, which probably also had an impact.
But is it still fair to assume that at least some prey species in South America have disappeared due to the arrival of a North American predator? It’s possible, but it’s difficult to disentangle this cause from climate change and other factors, Carrillo said.
Animal traits are forged in an evolutionary battlefield, but that doesn’t mean predators rise up to dominate their prey. Carrillo noted that if a predator were to eat its prey to extinction, it would have nothing to eat and would therefore also become extinct. If a predator has multiple prey, it could, in theory, survive by wiping out a species, but extinctions usually involve multiple factors.
Blackburn knows of no example of a natural invasion in which one species consumed another to extinction. “The natural world is inherently incredibly complicated, and it takes a tremendous amount of work to unravel the processes that typically take place,” he said.
Humans are clearly driving species to extinction through activities such as overhunting, habitat destruction, and the introduction of invasive species. “The fact that these effects are so dramatic is in itself almost strong evidence that these processes are real and very different from what happened before,” Blackburn said.
Originally posted on Live Science.