Mammals, birds and amphibians worldwide have lost on average 18% of their natural habitat range as a result of changes in land use and climate change, finds a new study.

The scientists estimate that species have lost an average of 18% of their natural habitat range sizes thus far, and may lose up to 23% by 2100.

The study (Robert M. Beyer and Andrea Manica, Historical and projected future range sizes of the world’s mammals, birds, and amphibians, Nature Communications, 2020; 11 (1) DOI: 10.1038/s41467-020-19455-9) published on November 6 in the journal Nature Communications, analyzed changes in the geographical range of 16,919 species from 1700 to the present day. The data were also used to predict future changes up to the year 2100 under 16 different climate and socio-economic scenarios.

A diverse abundance of species underpins essential ecosystem functions from pest regulation to carbon storage. Species’ vulnerability to extinction is strongly impacted by their geographical range size, and devising effective conservation strategies requires a better understanding of how ranges have changed in the past, and how they will change under alternative future scenarios.

Some species are more heavily impacted than others. A worrying 16% of species have lost over half their estimated natural historical range, a figure that could rise to 26% by the end of the century.

Species’ geographical ranges were found to have recently shrunk most significantly in tropical areas. Until around 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: clearance of rainforest for oil palm plantations in South East Asia, and for pasture land in South America, for example.

As humans move their activities deeper into the tropics, the effect on species ranges is becoming disproportionately larger because of a greater species richness in these areas, and because the natural ranges of these species are smaller to begin with.

The study results predict that climate change will have an increasing impact on species’ geographical ranges. Rising temperatures and changing rainfall patterns will alter habitats significantly, for example: other studies have predicted that without climate action, large parts of the Amazon may change from canopy rainforest to a savannah-like mix of woodland and open grassland in the next 100 years.

The results provide quantitative support for policy measures aiming at limiting the global area of agricultural land – for example by sustainably intensifying food production, encouraging dietary shifts towards eating less meat, and stabilizing population growth.

The conversion of natural vegetation to agricultural and urban land, and the transformation of suitable habitat caused by climate change are major causes of the decline in range sizes, and two of the most important threats to global terrestrial biodiversity.

“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 Dr Robert Beyer in the University of Cambridge’s Department of Zoology, first author of the report.

“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 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,” said Beyer.

He added: “We found that the higher the carbon emissions, the worse it gets for most species in terms of habitat loss.”

“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,” Professor Andrea Manica in the University of Cambridge’s Department of Zoology, who led the study.

He added: “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 report said:

Species’ vulnerability to extinction is strongly impacted by their geographical range size. Formulating effective conservation strategies therefore requires a better understanding of how the ranges of the world’s species have changed in the past, and how they will change under alternative future scenarios.

Their data reveal that range losses have been increasing disproportionately in relation to the area of destroyed habitat, driven by a long-term increase of land use in tropical biodiversity hotspots. The outcomes of different future climate and land use trajectories for global habitat ranges vary drastically, providing important quantitative evidence for conservation planners and policy makers of the costs and benefits of alternative pathways for the future of global biodiversity.

The report said:

Habitat range size is a strong predictor of species’ vulnerability to extinction. As a result, two major drivers of the decline of geographic range sizes — the conversion of natural vegetation to agricultural and urban land, and the transformation of suitable habitat caused by climate change — are considered two of the most important threats to global terrestrial biodiversity. Land-use change has caused staggering levels of habitat contractions for a range of mammal, bird, and amphibian species. Simultaneously, anthropogenic climate change has been driving shifts in species’ ranges, which, whilst resulting in larger range sizes for some species, has led to severe range retractions for others. Declines in global range sizes due to land-use and climate change heavily contribute to the loss of local species richness and abundance in many parts of the world, thereby threatening essential ecosystem functions. With global agricultural area potentially increasing drastically in the coming decades, and climate change continuing to drive ecosystem change at an accelerating pace, future projections suggest that past trends in range contractions may continue, and likely contribute to projected large-scale faunal extinctions.

The report said:

With moderate impacts on the habitat ranges of most species’ up until the industrial revolution, the expansion of agricultural production and settlements alongside the rise in population growth since the early 1800 s has drastically reduced range sizes of most mammals, birds, and amphibians.

It said:

Using potential natural ranges in 1850 as a reference, we estimate that species had lost an average of 18% of their natural habitat area by 2016. For most species, alterations in the global distribution of biomes due to past climatic change have had a much smaller effect on range sizes compared to land use, causing average range changes of <1% in the past 300 years. There is substantial variability between species in terms of the experienced range changes. Critical levels of habitat range loss affect a rapidly rising number of species, with currently 16% have lost more than half of their natural range. Among these species, tropical species account for an increasingly larger proportion, whereas small-ranged and threatened species did not experience significantly higher ranger losses than other species. For an estimated 18% of species, ranges have expanded in consequence of anthropogenic climate change and the conversion of unsuitable natural vegetation to cropland and pastures.

It said:

The magnitude of habitat range contractions estimated since 1700 is not merely the result of the increasing area of converted land. Over recent centuries, range loss has increased disproportionately in relation to the total size of agricultural and urban areas. Whilst the first billion hectares converted since 1700 caused an average 3% loss of habitat size, the most recently converted half billion hectares are responsible for an average loss of 6% of natural range sizes. This acceleration of marginal range losses can be explained by a long-term trend in the location of land-use change towards tropical regions, where both local species richness is higher and average ranges sizes are smaller, and thus where the destruction of natural habitat leads to particularly high relative range losses. Following a long period of much less land conversion than in other parts of the world, these areas have experienced a rapid expansion of agriculture since the end of the 19th century. Habitat conversion rates reached their highest levels to date in South America around the mid–late 20th century, and in the late 20th and early 21st century in South East Asia, a global hotspot of small-ranged species.


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