/Human activity impacts a quarter of the world’s threatened species

Human activity impacts a quarter of the world’s threatened species

Three generations of Bornean elephant pass through a palm oil plantation

Three generations of Bornean elephants pass through a palm oil plantation

Aaron Gekoski

A quarter of vulnerable vertebrate species are impacted by human-made threats to over 90 per cent of their habitat, and approximately 7 per cent are impacted by human activity across their entire range.

“These species will decline and possibly die out in the impacted parts of their habitat without conservation action. Completely impacted species will almost certainly face extinction,” says James Allan at the University of Queensland in Australia.

He and his colleagues mapped the habitats of 5457 threatened terrestrial birds, mammals and amphibians around the world. They divided the planet into a grid of 30 square kilometre boxes and determined within each the amount of human activity – crop and pasture land, built environment, night lights, hunting, roads and railways – and analysed the sensitivity each species has to these threats.

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These human impacts to species occur on over 84 per cent of the Earth’s surface and on average 38 per cent of a species’ range is impacted by one or more of them. Mammals are the most impacted with more than 52 per cent of each species’ range impacted on average. One third of all species are not exposed to these threats across any part of their range.

These findings may be conservative as they don’t take into account infectious diseases which are known to affect amphibian populations, or climate change, which impacts species across taxa, says Allan.

“Our understanding of threats to mammals is greater than for amphibians,” says Allan. This could partly explain why their results show mammals as the most impacted, despite amphibians generally being regarded as more threatened.

The top five countries most impacted by human activity were all in Southeast Asia, including Malaysia, Brunei and Singapore. On average, they have 120.3 species impacted per grid cell, while the global average is 15.6. The areas most impacted are mangroves, moist broadleaf forests in Brazil, Malaysia and Indonesia, and dry broadleaf forests in India, Myanmar and Thailand.

Southeast Asia also has the highest score for areas of refuge where there are no impacted species per grid cell, because it is so rich in biodiversity and some species aren’t as threatened by human activity. Other global refuges include Liberia, the Amazon rainforest, and Andes and Eastern Himalayan mountains, and tundra in the northern latitudes.

Journal reference: PLOS Biology, DOI: 10.1371/journal.pbio.3000158

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