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 A study unveiled on Monday showed that 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 fertilization in their
dung, urine and, after death, decomposing bodies.
The scientists said 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.
"In the past, abundant large free-ranging animals made nutrients
more evenly distributed, thus increasing global fertility,"
University of Oxford ecologist Christopher Doughty said.
 By traveling 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 percent of its former level, the
study found.
"In a sense, Earth was a land of giants before humans colonized the
planet," University of Vermont conservation biologist Joe Roman
said.
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 said.
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 said.
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Before commercial whaling cut global whale populations by up to 90
percent in recent centuries, whales and other marine mammals
transported around 750 million pounds (340,000 tonnes) of phosphorus
from depths of around 100 yards (meters) where they feed to the
sun-lit ocean surface annually, the researchers estimated. This has
declined to 23 percent 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 said.
The research was published in the Proceedings of the National
Academy of Sciences.
(Reporting by Will Dunham; Editing by Sandra Maler)
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