Human land use and climate change have deprived mammals, birds and amphibians of an average 18% of their natural habitats, according to a study of virtually all known species, and this could increase by up to 23% in the next eight decades.
That’s the worst outcome of widely varying projections, published in the journal Nature Communications, suggesting that targeted conservation planning could help mitigate the impact of these major threats to global biodiversity.
Humans have now sprawled over 40% of the world’s ice-free land, says lead author Robert Beyer from the University of Cambridge, UK, which is impacting animal ranges.
“Species’ range sizes are a strong predictor of their vulnerability to extinction,” he says, in turn jeopardising vital ecosystem functions which range from pest regulation to carbon storage.
Beyer and co-author Andrea Manica estimated the historical habitat ranges of nearly 17,000 species from the year 1700, using data on their global distribution and their preferred ecological conditions based on past climates and urban and agricultural land use.
They projected the analysis into 2100 based on 16 scenarios derived from five socio-economic and four emission forecasts – noting this doesn’t include other threats such as invasive species, hunting, pathogens, species’ mobility and habitat fragmentation.
Impacts on species varied widely, with 16% having lost more than half of their range so far. These were largely tropical animals, which have smaller ranges.
The tropics have also been most affected in more recent decades as large chunks of land have been cleared for crops such as soy and palm oil in South America and Asia, displacing a greater number of species per land area from these rich ecosystems.
“The tropics are biodiversity hotspots with lots of small-range species,” says Beyer. “If one hectare of tropical forest is converted to agricultural land, a lot more species lose larger proportions of their home than in places like Europe.”
In worst case scenarios, they found that up to a quarter of species could lose at least half of their habitat by 2100. Conversely, optimal projections predict this number could be reduced by 14%.
An important target involves restricting agricultural land use via sustainable, intensified production, dietary shifts and population growth reduction. Other measures include tropical forest regeneration and mitigating climate change.
The researchers hope their quantitative predictions – which Beyer says cover an unprecedentedly large number of species compared to related studies – will help policymakers take clear action on local and global levels to preserve biodiversity.
“Whilst our data quantify the drastic consequences for species’ ranges if global land use and climate change are left unchecked,” they write, “they also demonstrate the tremendous potential of timely and concerted policy action for halting and indeed partially reversing previous trends in global range restrictions.”