Public Release: 

On 58 percent of Earth's land surface, biodiversity has dropped below suggested 'safe' threshold

American Association for the Advancement of Science

Species "intactness" has dropped below what one research group considers the safe limit across about 58% of Earth's terrestrial surface, a new study reports. The results, part of perhaps the most comprehensive quantification of global biodiversity change to date, provide key insights into the current extent of biodiversity losses, which have been lacking to date. The Biodiversity Intactness Index (BII) captures changes in species abundance. Researchers hypothesize that below a so-called safe limit of biodiversity intactness, the wide range of services provided by biodiversity that underpin human well-being--such as crop pollination, waste decomposition, and regulation of the global carbon cycle--are critically threatened. Generally, the safe limit is placed at a precautionary 10% reduction in BII, meaning that species abundance within a given habitat is 90% of its original value in the absence of human land use. (Some researchers say that reductions can safely be as much as a 70%, however.) To quantitatively assess changes in BII globally, Tim Newbold et al. analyzed a database of more than 2.3 million records of greater than 39,100 species living in 18,600 sites - together representing a far more comprehensive dataset than evaluated in previous studies analyzing global biodiversity intactness. Their BII map reveals that global biodiversity has fallen to 84.6%. Even if the emergence of new species in a given region is accounted for, BII is still generally under the suggested threshold, at 88% of its original value. The impact of land-use pressures on biodiversity varies by biome, where grasslands are most affected, and tundra and boreal forests are least affected. Overall, analysis by Newbold et al. suggests that nine of the 14 terrestrial biomes have surpassed the suggested safe limit for biodiversity, although this number drops to seven out of 14 if the appearance of new species is included in the assessment. The authors note that the disparities between their model simulations that include the emergence of new species versus those that exclude it highlight the need to understand the effects of these new species on ecosystem function. A Perspective by Tom Oliver discusses this study in greater detail, highlighting how high levels of uncertainty around biodiversity change to date have appeared to hamper commitment to action in this space.

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