The devastating human impact on biodiversity

Biological diversity is under threat. More and more plant and animal species are disappearing world-wide, and humans are responsible. Until now, however, there has been no synthesis of the extent of human intervention in nature and whether the effects can be found everywhere in the world and in all groups of organisms. This is because most of the studies conducted to date have only looked at individual aspects.

To fill these research gaps, a team from the Swiss Federal Institute of Aquatic Science and Technology (Eawag) and the University of Zurich (UZH) have now conducted an unprecedented synthesis study. The researchers compiled data from around 2,100 studies that compared biodiversity at almost 50,000 sites affected by humans with the same number of reference sites that were not affected. The studies cover terrestrial, freshwater and marine habitats around the world, and all groups of organisms, from microbes and fungi to plants and invertebrates, fish, birds and mammals.

“It is one of the largest syntheses of the human impacts on biodiversity ever conducted world-wide,” says Florian Altermatt, professor of aquatic ecology at the University of Zurich and head of a research group at Eawag.

The findings of the study, which was published in the journal "Nature" in March, are unequivocal and leave no doubt as to the devastating impact that humans are having on biodiversity across the world. “Our findings show that all five factors have a strong impact on biodiversity world-wide, in all groups of organisms and in all ecosystems” says François Keck, a postdoctoral researcher at UZH, and lead author of the study.

On average, the number of species at impacted sites was almost 20 per cent lower than at unaffected sites. Particularly severe species losses across all biogeographic regions are found in vertebrates such as reptiles, amphibians and mammals. Their populations tend to be much smaller than those of the invertebrates, increasing the probability of extinction.

Species communities are shifting

The species composition at a location is a second key aspect of biodiversity, in addition to the number of species. In high mountain regions, for example, specialised plants are at risk of being displaced by species from lower altitudes as the climate warms. In some circumstances, the number of species at a particular site may remain the same; nevertheless, biodiversity and its ecosystem functions will be affected if, for example, a plant species disappears that has particularly good root systems to protect the soil from erosion.

The greatest shifts in the species communities are found among tiny microbes and fungi. “This could be because these organisms have short life cycles and high dispersion rates, and therefore respond more quickly,” says Keck.

According to the study, environmental pollution and habitat changes have a particularly negative impact on the number of species and the composition of species communities. According to Altermatt, habitat changes are often very drastic, for example, when people cut down a forest or level a meadow.

Pollution, whether accidental, as in the case of an oil tanker spill, or deliberate, e.g. when pesticides are sprayed, introduces new substances into a habitat that destroy or weaken the organisms living there. The findings do not mean that climate change is less problematic for biodiversity in comparison, says Altermatt. “However, it is likely that the full extent of its impact cannot yet be verified today.”

The findings are cause for alarm

The third key aspect of biodiversity that the research team investigated was the homogeneity, or how similar species communities are at different sites. For example, large-scale, intensive agriculture tends to make landscapes more homogeneous, and the species communities they contain more similar. The effects were mixed, with some studies showing a very strong tendency towards homogenisation, and others demonstrating a tendency for species communities to become more diverse, especially at local level.

However, the researchers doubt that the latter is a good sign. They speculate that increasing dissimilarities could also be a temporary effect in severely impacted habitats.

According to the authors, the study can serve as benchmarks for future biodiversity research and conservation efforts. “Our findings provide clear indications of which human influences are having the greatest impact on biodiversity,” says Keck. “This also shows what goals need to be set if these trends are to be reversed.”
(UZH/wi)

Reference:

François Keck et al. (2025): The global human impact on biodiversity. DOI: 10.1038/s41586-025-08752-2

https://www.nature.com/articles/s41586-025-08752-2