The geographical ranges of most animals are shrinking worldwide

The compounding effects of climate change and human development have spoiled the natural habitats of most mammals, birds, and amphibians by an average of 18 percent. A new study from the University of Cambridge suggests that the geographical ranges of animals will continue to shrink worldwide, and that nearly a quarter of these ecosystems will be lost by the end of the century. 

The researchers analyzed changes in the geographical ranges of nearly 17,000 species over more than three centuries. The team used this data to predict future changes under 16 different scenarios.

A diverse range of species is needed to perform critical ecosystem functions from pest regulation to carbon storage. The vulnerability of any given species to extinction is strongly impacted by the size of its geographical range. In order to develop effective conservation strategies, experts need to understand how ranges have changed in the past and how they will change in the future.

“The habitat size of almost all known birds, mammals, and amphibians is shrinking, primarily because of land conversion by humans as we continue to expand our agricultural and urban areas,” said study first author Dr. Robert Beyer.

The impacts are disproportionately distributed, with some species more severely affected than others. For example, an alarming 16 percent of species have lost over half of their estimated historical range, and this number of species could grow to 26 percent in the coming decades. 

More recently, the most significant losses of geographical ranges were found in tropical areas. Up until about 50 years ago, most agricultural development was in Europe and North America. Since then, large areas of land have been converted for agriculture in the tropics.

“The tropics are biodiversity hotspots with lots of small-range species. 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,” said Dr. Beyer.

“Species in the Amazon have adapted to living in a tropical rainforest. If climate change causes this ecosystem to change, many of those species won’t be able to survive – or they will at least be pushed into smaller areas of remaining rainforest. We found that the higher the carbon emissions, the worse it gets for most species in terms of habitat loss.”

The clearing of land for agricultural and urban development and climate change are the main drivers of the decline in geographical range sizes, and two of the biggest threats to global terrestrial biodiversity.

Study lead author Andrea Manica is a professor in the Department of Zoology at the University of Cambridge.

“Whether these past trends in habitat range losses will reverse, continue, or accelerate will depend on future global carbon emissions and societal choices in the coming years and decades,” said study lead author Professor Andrea Manica.

“While our study quantifies the drastic consequences for species’ ranges if global land use and climate change are left unchecked, they also demonstrate the tremendous potential of timely and concerted policy action for halting – and indeed partially reversing – previous trends in global range contractions. It all depends on what we do next.”

The study is the published in the journal Nature Communications.

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By Chrissy Sexton, Earth.com Staff Writer