By Biomass, Humans Have Eliminated Half of the World’s Plants and Over 80% of the World’s Wild Mammals

Staggering statistics, being a warning that humans can eliminate their own species at scale (through nuclear weapons or climate change, for instance) if they fail to be careful enough.

While scientists and conservationists grow increasingly worried about the world’s biodiversity, a new study that sought to estimate the biomass of all living creatures on Earth has shed some light on humanity’s impact.

The planet is largely dominated by plants, which make up 82 percent of all life on Earth, followed by bacteria at 13 percent, and the remaining five percent is everything else, including 7.6 billion human beings.

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According to the study, published Monday by the Proceedings of the National Academy of Sciences of the United States of America (PNAS), people only make up 0.01 percent of the Earth’s biomass—however, their impact has been massive.

The researchers estimate that, in terms of biomass, the so-called rise of human civilization has destroyed 83 percent of wild mammals, 80 percent of marine animals, 50 percent of plants, and 15 percent of fish.

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Biodiversity Losses Increase Risks of Domino Effect of Further Extinctions

This phenomenon is referred to as an “extinction cascade.”

New research shows that the loss of biodiversity can increase the risk of “extinction cascades,” where an initial species loss leads to a domino effect of further extinctions.

The researchers, from the University of Exeter, showed there is a higher risk of extinction cascades when other species are not present to fill the “gap” created by the loss of a species.

Even if the loss of one species does not directly cause knock-on extinctions, the study shows that this leads to simpler ecological communities that are at greater risk of “run-away extinction cascades” with the potential loss of many species.

With extinction rates at their highest levels ever and numerous species under threat due to human activity, the findings are a further warning about the consequences of eroding biodiversity.

“Interactions between species are important for ecosystem (a community of interacting species) stability,” said Dr Dirk Sanders, of the Centre for Ecology and Conservation at the University of Exeter’s Penryn Campus in Cornwall. “And because species are interconnected through multiple interactions, an impact on one species can affect others as well.

“It has been predicted that more complex food webs will be less vulnerable to extinction cascades because there is a greater chance that other species can step in and buffer against the effects of species loss.

“In our experiment, we used communities of plants and insects to test this prediction.”

The researchers removed one species of wasp and found that it led to secondary extinctions of other, indirectly linked, species at the same level of the food web.

This effect was much stronger in simple communities than for the same species within a more complex food web.

Dr Sanders added: “Our results demonstrate that biodiversity loss can increase the vulnerability of ecosystems to secondary extinctions which, when they occur, can then lead to further simplification causing run-away extinction cascades.”

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The loss of a predator can initiate a cascade, such as in the case of wolves, where their extinction on one mountain can cause a large rise in the number of deer. This larger number of deer then eats more plant material than they would have before. This reduction in vegetation can cause extinctions in any species that also relies on the plants, but are potentially less competitive, such as rabbits or insects.

Add this research to one of the many reasons why rigorously addressing climate change — which can destabilize environments — is of paramount importance.

Study: Political Instability is the Biggest Cause of Species Loss

The class struggle between people poor and people rich is often at the root of conflict in society. It should be simple enough for a rational person to see that in their own country. In some places though, that struggle is a lot worse than it is in others.

A vast new study of changes in global wildlife over almost three decades has found that low levels of effective national governance are the strongest predictor of declining species numbers — more so than economic growth, climate change or even surges in human population.

The findings, published in the journal Nature, also show that protected conservation areas do maintain wildlife diversity, but only when situated in countries that are reasonably stable politically with sturdy legal and social structures.

The research used the fate of waterbird species since 1990 as a bellwether for broad biodiversity trends, as their wetland habitats are among the most diverse as well as the most endangered on Earth.

An international team of scientists and conservation experts led by the University of Cambridge analysed over 2.4 million annual count records of 461 waterbird species across almost 26,000 different survey sites around the world.

The researchers used this giant dataset to model localised species changes in nations and regions. Results were compared to the Worldwide Governance Indicators, which measure everything from violence rates and rule of law to political corruption, as well as data such as gross domestic product (GDP) and conservation performance.

The team discovered that waterbird decline was greater in regions of the world where governance is, on average, less effective: such as Western and Central Asia, South America and sub-Saharan Africa.

The healthiest overall species quotas were seen in continental Europe, although even here the levels of key species were found to have nosedived.

This is the first time that effectiveness of national governance and levels of socio-political stability have been identified as the most significant global indicator of biodiversity and species loss.

“Although the global coverage of protected areas continues to increase, our findings suggest that ineffective governance could undermine the benefits of these biodiversity conservation efforts,” says Cambridge’s Dr Tatsuya Amano, who led the study at the University’s Department of Zoology and Centre for the Study of Existential Risk.

“We now know that governance and political stability is a vital consideration when developing future environmental policies and practices.”