by The combined weight of Earth’s wild land mammals – from elephants to bison and from deer to tigers – is now less than 10% of the combined tonnage of men, women and children living on the planet.
A study by scientists at Israel’s Weizmann Institute of Science, published this month, concludes that wild land mammals alive today have a total mass of 22 million tons. For comparison: the human race today weighs a total of around 390 million tons.
At the same time, the species we domesticate, such as sheep and cattle, and other companions, such as urban rodents, add another 630 million tons to the total mass of creatures now competing with wild mammals for Earth’s resources. The biomass of pigs alone is almost twice that of all wild land mammals.
The numbers clearly show that mankind’s conversion of the planet’s wilderness and natural habitats into one vast global plantation is now well under way – with devastating consequences for their wild creatures. As the study authors point out, the notion that Earth is a planet that still has vast plains and jungles teeming with wild animals is now seriously off the mark. The natural world and its wild animals are disappearing while the human population of nearly eight billion people continues to grow.
“When you watch television documentaries about wildlife — for example, wildebeest migration — it’s easy to conclude that wild mammals are doing quite well,” said lead author Ron Milo observer.
“But that intuition is wrong. These creatures are not doing well at all. Their total mass is about 22 million tons, which is less than 10% of humanity’s total weight and accounts for only about 6 pounds of wild land mammals per person. And if you add all of our cattle, sheep and other livestock, that’s another 630 million tons. That’s 30 times the total for wildlife. It’s breathtaking. This is a wake-up call to humanity.”
The study, The Global Biomass of Wild Mammals, also shows that those that do best — like the white-tailed deer in the US and wild boar — are those that can more easily adapt to the presence of humans. Both species are found near settlements and are occasionally treated as pets. “Even in the wild, humankind’s fingerprints are evident,” added Milo, whose team’s study was published in the US journal Proceedings of the National Academy of Sciences.
As part of the paper, researchers Lior Greenspoon and Eyal Krieger collected biomass data from about half of all known mammals and used computer learning models on other zoological samples to calculate the other half.
The dire numbers for land mammals have been outstripped by those in the oceans. The total mass of marine mammals has been calculated at around 40 million tons. Fin whales have the largest total biomass, with sperm whales and humpback whales coming in second and third, respectively.
The mass ratios of domesticated to wild animals emphasize the active role that humans play in shaping the abundance of mammals on earth
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Common pet species have also been found to be a significant contributor to humankind’s impact on the planet. Domestic dogs have a total mass of about 20 million tons, a figure close to the combined biomass of all wild land mammals, while cats have a total biomass of about 2 million tons, almost twice that of the African savannah elephant. “These domesticated-to-wild mass ratios underscore the active role humans play in shaping the abundance of mammals on Earth,” the researchers note in their publication.
Biomass studies are not the only way to quantify wildlife. The number of species is also revealing. For example, it has been found that there are 1,200 bat species, accounting for one-fifth of all land mammal species and two-thirds of all individual wild mammals by head count. However, they make up only 10% of the biomass of wild land mammals.
“Biomass complements species richness and other diversity metrics and can serve as an indicator of the abundance and ecological footprint of wild mammals on a global scale,” the researchers explain.
The team’s estimates, made two years ago, suggest there are about 50 million tons of wild mammals on Earth. The new figure, calculated using a variety of techniques including AI, shows that the crisis facing the planet’s wildlife appears to be far worse than first thought. The rate at which wild mammal depletion is occurring is now an urgent need to be assessed, they say, and is the focus of the next phase of the study, which looks at how much biomass has been lost over the past 100 years.
