In one of the largest syntheses of the human impacts on biodiversity ever conducted worldwide, a team from the Swiss Federal Institute of Aquatic Science and Technology (Eawag) and the University of Zurich looked at terrestrial, freshwater and marine habitats, as well as including all groups of organisms, including microbes, fungi, plants, invertebrates, fish, birds and mammals. From a synthesis of 2,000 global studies, which accounted for nearly 100,000 sites across all continents, they concluded human activities had “unprecedented effects on biodiversity”. Not only is the number of species declining, but the composition of species communities is also changing.
Photo: Rijk van de Kaa
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 of the studies conducted to date have only looked at individual aspects, either a single location or a specific human impact, making it difficult to assert any general statements about the effects and impacts of humans on biodiversity.
On average, the number of species at human-impacted sites was almost 20% lower than at sites unaffected by humans. The paper reported particularly severe losses among reptiles, amphibians and mammals, whose populations are often smaller than invertebrates, which increases the chances of extinction.
Their analysis covered five drivers of decline: habitat change, direct exploitation of resources (such as hunting or fishing), climate change, invasive species and pollution, revealing 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.
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. The full extent of climate change and how it affects species is also not entirely understood. According to the authors, the study exemplifies that changes in biodiversity should not be based solely on changes in the number of species. The findings are alarming due to their distinctness and global validity and can also serve as benchmarks for future biodiversity research and conservation efforts.