What happens when you remove all the biggest animals from the ocean? Nonetheless, this pattern has changed in the last half thousand years. And there’s growing evidence that, over the most recent 50,000 years or so, once humans colonize a new environment, the extinction of the largest animals living there tends to follow very closely. “In a sense, we’re driving evolution [toward smaller individuals]”, Payne said.
Advertisement
The researchers made this determination by examining the relationship betwen risk of extinction and body size over the last 500 eyars for mollusks and invertebrates, and then comparing modern extinction patterns to ancient ones.
“We used the fossil record to show, in a concrete, convincing way, that what is happening in the modern oceans is really different from what has happened in the past”, said study co-author Noel Heim, a postdoctoral researcher in Payne’s lab. “Biologically, we are going into uncharted territory”.
Although the research did not consider the question of why the largest ocean animals are at greater risk, the working theory from the authors is that humans are targeting the bigger creatures. He said that humans have the opportunity to totally avert this if they would make the right decisions. The area is home to “many species of deep-sea coral, sharks, sea turtles, seabirds and deep-diving marine mammals, such as beaked whales and sperm whales”, the Washington Post explains, as well as underwater canyons and mountains.
“Big animals are important in themselves, but removing them could also dramatically change marine ecology and the way oceans work”, said Pimm.
For the study, the researchers conducted a statistical analysis of almost 2,500 samples of both extinct and living sea creatures. They identified which marine animals are now at risk of dying out by checking the list of threatened species compiled by the International Union for the Conservation of Nature.
Meanwhile, extinction selectivity was measured according to body size, habitat zone, motility and whether the animals were predators or not. That’s something unheard of in Earth’s long history of mass extinctions, a new study finds.
He added: ‘We have had mass extinctions before. So if we think about the things people like to eat, like tuna and salmon, these are large fish relative to the average fish in the ocean.
If those environmental changes are indeed the main threats to marine species today as well, the authors expected to see similar patterns of extinction in terms of which animals are most at risk.
The danger is disproportionate to the percentage of threatened species, with the authors warning the loss of giants would “disrupt ecosystems for millions of years even at levels of taxonomic loss far below those of previous mass extinctions”. Payne was five years old when Luis and Walter Alvarez published their now-famous theory that a massive asteroid slammed into the Earth roughly 65 million years ago, ultimately bringing about the demise of the dinosaurs.
He points to the humpback whale and northern elephant seal as species that have come back from the brink of extinction due to conservation measures.
The sixth mass extinction-the one that seven billion humans are doing their darnedest to trigger at this very moment-is shaping up to be like nothing our planet has ever seen. There have been only 15 extinctions of marine animals during that time. There are countless species of marine invertebrates that we simply don’t have enough data on to do a proper threat assessment.
“After looking at the fossil record and then looking at fisheries studies, we can’t think of anything but human hunting that might be the cause of this very odd size selectivity”, Heim said.
This body size finding, according to Payne, is consistent with the fact that humans preferentially fish from the top of the food web: We tend to go after larger creatures because they provide more food. Payne concentrated on oceans, where the fossil records are better over time. For instance, there are fewer than 100 individuals of a species of porpoise called the vaquita left in the world. “As a result, terrestrial ecosystems were locked into a new trajectory that included local biodiversity loss over and above the loss of the large animals themselves, and changes in which kinds of plants dominated”.
Advertisement
‘You can’t imagine a world without them.
