Biodiversity Under Threat: Largest Synthesis Study Reveals Extent

This is shown by a study by the University of Zurich and Eawag published in the journal “Nature”. It is one of the largest investigations ever conducted on this topic.

Biological diversity is under threat. Plant and animal species are disappearing around the world at an ever-increasing rate. Humans are responsible for this. Until now, however, a synthesis has been lacking as to which human interventions in nature are how severe, and whether the effects can be found everywhere in the world and across all groups of organisms. More on biodiversity and hobby hunters.

To close these research gaps, a team from the University of Zurich (UZH) and the water research institute Eawag has now conducted a synthesis study without equal. The researchers compiled data from around 2’100 studies comparing biodiversity at nearly 50’000 human-impacted sites with an equal number of unaffected reference sites. The studies cover terrestrial, freshwater and marine habitats across the globe, as well as all groups of organisms: from microbes and fungi to plants and invertebrates, through to fish, birds and mammals. “It is one of the largest syntheses ever conducted worldwide on the effects of humans on biodiversity,” says Florian Altermatt, UZH Professor of Aquatic Ecology and head of a research group at Eawag.

Species Numbers Declining Significantly

The results of the study just published in the journal «Nature» are unequivocal — and leave no doubt about the devastating impact humans are having on biodiversity worldwide. «We examined the effects of the five most important human drivers of biodiversity loss: habitat change, direct exploitation such as hobby hunting or fishing, climate change, pollution, and invasive species», says François Keck, postdoctoral researcher in Altermatt's research group and lead author of the study. «Our results show that all five factors have strong negative impacts on biodiversity — globally, across all organism groups and all ecosystems.» As studies demonstrate,hobby hunting fails as a population control measure.

On average, species numbers at impacted sites were nearly one-fifth lower than at unaffected reference sites. Particularly severe species losses across all biogeographical regions are found among vertebrates such as reptiles, amphibians, and mammals. Their populations are generally far smaller than those of invertebrates, which increases the probability of extinction.

Species communities are shifting

The impacts, however, extend far beyond the loss of species. «It is not only species numbers that are declining», says Keck. «Under human pressure, the composition of species communities is also changing.» The species composition at a given site is, alongside the sheer number of species, a second key aspect of biodiversity. In high mountain regions, for example, specialized plants are at risk of being displaced by species from lower altitudes due to climate warming. The most pronounced shifts in species communities are occurring among tiny microbes and fungi. «This may be because these organisms have short life cycles and high dispersal rates, allowing them to respond more rapidly», says ecologist Keck.

According to the study, pollution and habitat change have a particularly negative effect on species numbers and the composition of species communities. More onenvironmental and nature conservation.

Results are a warning signal

As the third key aspect of biodiversity, the research team examined so-called homogeneity — that is, how similar species communities are across different locations. Large-scale, intensive agriculture, for example, causes landscapes — and the species communities found within them — to become more homogeneous, meaning more similar.

The researchers are skeptical, however, that the latter is a positive sign. “The human influence we find is in some cases so strong that there are even signs that could indicate a complete collapse of species communities,” says Altermatt.

According to the authors, the study demonstrates on the one hand that changes in biodiversity should not be assessed solely on the basis of changes in species numbers. On the other hand, the results serve as a warning signal due to their clarity and global validity. “Our results provide clear indications of which human influences impair biodiversity and to what extent,” says François Keck. “From this, one can also determine what goals must be set if one wishes to reverse these trends.”

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