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Humans are driving biodiversity loss among all species across the planet, according to a synthesis of more than 2,000 studies.
The exhaustive global analysis leaves no doubt about the devastating impact humans are having on Earth, according to researchers from the Swiss Federal Institute of Aquatic Science and Technology (Eawag) and the University of Zurich. The study – which accounted for nearly 100,000 sites across all continents – found that human activities had resulted in “unprecedented effects on biodiversity”, according to the paper, published in Nature.
Florian Altermatt, professor of aquatic ecology at the University of Zurich and head of Eawag, said: “It is one of the largest syntheses of the human impacts on biodiversity ever conducted worldwide.”
The team looked at terrestrial, freshwater and marine habitats, as well as including all groups of organisms, including microbes, fungi, plants, invertebrates, fish, birds and mammals.
Human pressures distinctly shifted community composition (essentially, which species live where) and decreased local diversity, researchers found. On average, the number of species at human-impacted sites was almost 20% lower than at sites unaffected by humans.
Particularly severe losses were recorded among reptiles, amphibians and mammals, according to the paper. Their populations are often smaller than invertebrates, which increases the chances of extinction.
The analysis covered five drivers of decline: habitat change, direct exploitation of resources (such as hunting or fishing), climate change, invasive species and pollution.
François Keck, lead author and a postdoctoral researcher in Altermatt’s research group, said: “Our findings show that all five factors have a strong impact on biodiversity worldwide, in all groups of organisms and in all ecosystems.”
Pollution and habitat changes, often driven by agriculture, have a particularly negative impact on biodiversity. Intensive agriculture – especially arable farming – involves large amounts of pesticides and fertilisers, which result in a decline of biodiversity, but also shifts the composition of species. The full extent of climate change and how it affects species is not entirely understood.
While the overall effect of human intervention was negative, some ambiguities remained: human impact on wildlife varied by location, as did the degree to which biodiversity was homogenised by human activity, researchers said.
Before this paper there had never been an attempt to combine findings from such a large number of biodiversity research studies examining humans’ impact everywhere on the planet and in all groups of organisms; most studies were limited to looking at either a single location or a specific human impact. This meant it was difficult to make general statements about the impacts of human activity on biodiversity, researchers say.
Keck said: “It’s not just the number of species that is declining. Human pressure is also changing the composition of species communities.”
In mountainous areas, for example, specialised plants are being replaced by those that typically grow at lower altitudes. This process is known as the “elevator to extinction” as high-altitude plants have nowhere else to go. This could mean that while the number of species might remain the same, the diversity is reduced.
“Bending the curve of contemporary biodiversity loss and change is one of the greatest challenges facing our society,” the researchers stated. They said the paper should provide an “important benchmark” for the development and assessment of future conservation strategies.
Lynn Dicks, professor of ecology at Cambridge University, described it as a “useful and important analysis”, but said the findings revealed “no great surprises”.
She said: “We know that humans are hugely changing biodiversity across the planet, causing new and different communities of plants, animals and microbes to form, which can cope with the sometimes very harsh conditions we create.
“A big concern for me is how to ensure that those species that can live alongside us, many of which provide key ecological functions like pollination, decomposition and seed dispersal, have large enough populations and enough genetic diversity to continue evolving.”
Prof Alexandre Antonelli, director of science at Kew Gardens, said the paper showed with “unprecedented clarity the ubiquitous negative influence of human activities on nature”.
He added: “This is an excellent piece of research that demonstrates the importance of biological inclusion – from plants and fungi to mammals and fish – in assessing the impact of humans on biodiversity at local, regional and global scales.”
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