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The world's ecosystem needs fertilisation from large mammals, this fertilisation comes from their dung, urine and, after death, their decomposing bodies. Photo: Reuters
You can call it the fertilisation cessation, and scientists say it has had a disruptive effect on ecosystems around the world.
A study unveiled showing the extinction or precipitous population declines of large land and sea mammals starting at the end of the last Ice Age and continuing through today has deprived ecosystems of a vital source of fertilisation in their dung, urine and, after death, decomposing bodies.
The scientists say that these large mammals including whales, mammoths, mastodons, ground sloths, rhinos, huge armadillos as well as seabirds and migrating fish like salmon played a key role in making Earth fertile by spreading nutrients across oceans, up rivers and deep inland.
The elephant’s cousin, the mastodon, was responsible for keeping the world fertile with their dung. Photo: AFP
“In the past, abundant large free-ranging animals made nutrients more evenly distributed, thus increasing global fertility,” University of Oxford ecologist Christopher Doughty says.
By travelling long distances, these large mammals transported and recycled nutrients like phosphorous and nitrogen to far-flung ecosystems, boosting their productivity. This capacity to spread nutrients away from concentrated sources on both land and sea to other ecosystems has plummeted to 6 per cent of its former level, the study found.
Many of the large animals that are in danger of going extinct are responsible for fertilising the world. Photo: Reuters
“In a sense, Earth was a land of giants before humans colonised the planet,” University of Vermont conservation biologist Joe Roman says.
About 150 species of large mammals went extinct around 10,000 years ago, many due to a combination of human hunting and climate change, Roman says.
Of 48 species of the very largest plant-eating land mammals alive during the Ice Age, including 16 species of elephants and their relatives, nine rhinoceros species and eight giant sloth species, only nine remain, none in the Americas, Doughty says.
Before commercial whaling cut global whale populations by up to 90 per cent in recent centuries, whales and other marine mammals transported around 750 million pounds (340,000 tonnes) of phosphorus from depths of around 100m where they feed to the sun-lit ocean surface annually, the researchers estimated. This has declined to 23 per cent of its former level.
“Great whales such as humpbacks, blue whales and sperm whales often dive deep to feed, coming to the surface to breathe and digest. They also defecate, or poop, at this time, releasing important nutrients such as nitrogen and phosphorous. These nutrients can enhance the growth of algae, invertebrates even fish,” Roman says.
The research was published in the Proceedings of the National Academy of Sciences. – Reuters
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