For hundreds of millions of years, earth has been a planet of giants. But in the last few thousand years, these large animals and plants “have been whittled away”, and this process continues”.
Their loss, says Professor Yadvinder Malhi, leader of the ecosystems group at the Environmental Change Institute at the University of Oxford, “matters to the very fabric of life on earth and why we must do everything possible to protect and restore them”.
He is one of a team of authors of a new paper, The Megabiota are Disproportionately Important for Biosphere Functioning, which finds how protecting large animals such as elephants, rhinos and whales, and large trees such as redwoods, sequoias and mountain ash, will have a disproportionate positive impact on biodiversity, ecosystem processes, and climate mitigation.
These large animals are often seen as charismatic and used as flagship species for conservation decisions. But many are imperilled by habitat loss, hunting, logging and climate change.
The research finds that not only are larger plants and animals at a higher risk of extinction, but their loss would fundamentally degrade life on earth.
The study, published in the journal Nature Communications this week, shows that the continued loss of large animals alone would lead to a 44% reduction in the total amount of wild animal biomass on the planet and a 92% reduction in soil fertility, which underpins the ability of the earth to grow plants and sustain life.
The study was conducted by researchers at the University of Arizona, the Santa Fe Institute, Northern Arizona University, the UN Environment Programme World Conservation Monitoring Centre and the University of Oxford.
A key reason for the findings lies in the transport of nutrients, says the Environmental Change Institute. “When large animals eat in one location and defecate or urinate in another, they transport nutrients, often moving them from nutrient-rich areas to other, less fertile, parts of the land and oceans.
“The research also highlighted that forests with larger trees disproportionately stored more biomass carbon and were more productive.”
“Simply put, landscapes and ecosystems that contains larger and more abundant organisms are more productive, more resilient to climate change, and will provide disproportionately more ecosystem services to humanity,” state the authors.
Ecosystems devoid of large animals and trees are less resilient to change, less predictable and can collapse more easily.
The findings, says the institute, help answer an ongoing debate about where to channel limited conservation resources, showing that protecting big, charismatic species has an umbrella effect to protect the wider ecosystem “and everything that lives in it”.
“This research shows there are fundamental scientific principles that explain why large animals and trees matter for the health and integrity of all life on earth”, says lead author Prof Brian Enquist of the University of Arizona, in a statement.
The researchers note how since the rise of humanity it’s primarily the largest and oldest trees that have become disproportionately rarer and more threatened.
“Climate change and shifts in localised climate due to deforestation is now disproportionately impacting big and old trees.
“Large trees are declining in forests at all latitudes,” they said.
The average body mass of mammals on all the continents, particularly predators has dropped precipitously with the spread of humans around the world, with almost a quarter of large species at risk.
Marine mammals, too, have experienced broad population reductions from widespread hunting over the past few hundred years.
Smaller organisms are not less important or should be ignored. “Indeed the role of the smaller organisms (microbes, insects, etc.) are crucial to ecosystem and biosphere functioning.
“Our point is that the functioning of the biosphere and the well-being of increasingly smaller organisms disproportionately relies on the largest organisms. Further, the smaller organisms cannot provide most of the distinctive ecological roles and services played by large old trees and animals.”