Has human land use pushed biodiversity loss beyond safe limits?
Newbold, Tim, et al. “Has land use pushed terrestrial biodiversity beyond the planetary boundary? A global assessment.” Science 353.6296 (2016): 288-291. DOI: 10.1016/j.jclepro.2016.09.117.
Humans have altered the face of the Earth for food, fuel, fiber, and living spaces. Changing original ecosystems could harm biodiversity ultimately reducing ecosystem function. A recent study examined whether the current state of biodiversity loss indeed bodes ill for ecosystem functioning.
To assess whether biodiversity has been pushed beyond potentially safe limits, the a team of researchers led by Tim Newbold from the United Nations Environment Programme’s World Conservation Monitoring Centre used a metric called the Biodiversity Intactness Index, or BII. BII estimates whether a species increases, decreases, or stays the same in relation to its original numbers when its living spaces are perturbed or lost.
To estimate BII, the researchers used a large database of hundreds of studies conducted at thousands of sites worldwide. The database is called PREDICTS (Projecting Responses of Ecological Diversity in Changing Terrestrial Systems). These studies — conducted for many different plants, insects, birds, amphibians, and mammals — examined how a species or groups of species (communities) change with human land use.
First the researchers tested how changes in species richness and across different ecosystems are related to land-use type, land-use intensity, human population, and proximity to roadways. In their statistical models, the researchers accounted for differences among studies in methods, area and intensity of sampling, and species. Then, for the entire world, the researchers calculated the numbers for what have been suggested as safe limits for biodiversity loss. Crossing safe limits for any area is measured as losses of over 20 percent of the original species set — called species richness — or 10 percent of the numbers of all species.
The researchers found that, on average, species numbers in their natural habitat had fallen by 8 to 18 percent, clearly over the 10-percent safe limit. Similarly, species richness had fallen below the 20-percent safe limit of loss. All ecosystems showed signs of harm — nine of 14 ecosystems had crossed the proposed planetary boundary. Changes were most pronounced in grasslands. As expected, biodiversity hotspots — world regions where high biodiversity overlaps with high human impacts — had suffered the most. In comparison, three of five global areas identified as “high biodiversity wilderness” had not crossed safe limits.
Importantly, this study found that between 40 and 70 percent of Earth’s ecosystems have likely been pushed beyond safe limits. However, many more questions remain about how losing species can change the way ecosystems benefit humans. Is it just the numbers that are important, or should we pay attention to species type as well? Do new species serve the same functions as the ones lost? Can new species do more damage to ecosystem services? Future research might reveal more insights into which aspects of biodiversity are most critical to ecosystem function.