Human pressure is changing biodiversity faster than we realize

Humans are having a highly detrimental impact on biodiversity worldwide. Not only is the number of species declining, but the composition of species communities is also changing. 

These are the findings of a study by the Swiss Federal Institute of Aquatic Science and Technology (Eawag).

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

Many previous studies have addressed the threat of species loss. Yet most such efforts focused on particular ecosystems, a single human activity, or localized conditions, making it challenging to draw broad conclusions. 

This new study attempts an unprecedented synthesis: it compares nearly 50,000 sites around the world subject to human influence with an equal number of reference sites that remain relatively untouched. 

By covering terrestrial, freshwater, and marine environments and targeting everything from microbes and fungi to larger organisms such as fish, birds, and mammals, the researchers provide a uniquely comprehensive snapshot of biodiversity challenges across the globe.

Human pressures on ecosystems

The project examines the five principal human activities that affect biodiversity: habitat modification, direct exploitation (e.g., hunting or fishing), climate change, pollution, and invasive species. 

“We analyzed the effects of the five main human impacts on biodiversity: habitat changes, direct exploitation such as hunting or fishing, climate change, pollution and invasive species,” said lead author François Keck, a scientist at Eawag.

“Our findings show that all five factors have a strong impact on biodiversity worldwide, in all groups of organisms and in all ecosystems.”

Species numbers at impacted sites

One clear outcome is that species numbers at impacted sites were nearly 20% lower than at unaffected ones.

Vertebrates such as reptiles, amphibians, and mammals stand out for their major declines, likely because they typically have smaller population sizes and can vanish more readily.

However, beyond just the loss of species, the researchers also documented considerable shifts in the types of species that persist under human pressure. 

“It’s not just the number of species that is declining,” Keck noted. “Human pressure is also changing the composition of species communities.” 

That means even if the overall number of species remains the same at a site, the functions those species perform might be different, leading to potential disruptions in ecosystem services and stability.

Drastic changes from human pressure

Environmental pollution and habitat loss emerged from the study as especially damaging. Habitat modification frequently involves stark, abrupt transformations of a region – for example, clearing forests or converting grasslands to farmland. 

Pollution introduces hazardous substances into the ecosystem, including everything from oil spills to agricultural pesticides. These drastic changes can weaken or kill resident organisms.

In contrast, climate change – though likely a major long-term threat – did not stand out as prominently within the timeframe of data analyzed, which Altermatt attributes to potential time lags. “However, it is likely that the full extent of its impact cannot yet be verified today,” he said.

Homogenization – or collapse?

Another important finding concerns the degree of similarity among different species communities (often termed “homogenization”). Large-scale farming tends to homogenize landscapes, making ecological communities more uniform. 

But the study also uncovered cases where communities grew more dissimilar from one another, particularly in severely impacted locations.

“The human influence that we find is sometimes so strong that there are even signs that could indicate a complete collapse of the species communities,” Altermatt explained. Such changes might reflect temporary upheavals in biodiversity that could herald further declines.

Implications for conservation

One critical lesson from this study is that measuring biodiversity strictly by counting species may overlook significant community-level changes. 

A site could hold the same number of species as before, yet the particular species present could shift in ways detrimental to essential ecosystem services – like pollination, soil stability, or water purification.

The magnitude and universality of the findings “provide clear indications of which human influences are having the greatest impact on biodiversity,” Keck said. “This also shows what goals need to be set if these trends are to be reversed.”

Though every region and ecosystem experiences different pressures, the authors hope the results offer a sort of benchmark. Policymakers, conservationists, and land managers could lean on these large-scale insights as they devise more localized strategies to safeguard biodiversity. 

For instance, focusing on preserving or restoring specific habitats, curbing pollution, or carefully managing invasive species might bring tangible benefits more swiftly than previously realized.

Humans alter ecosystems worldwide

Ultimately, the study emphasizes that humans are altering the face of ecosystems worldwide – not just through outright loss of species, but also by reshaping the composition of those that remain.

The authors warn that these changes can reverberate throughout ecosystems, undermining everything from pollinator networks to fisheries. 

As the scientists emphasize, the next step is to use these insights to inform meaningful action on behalf of the countless species that still share our planet.

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