The ongoing expansion of human activity in pristine nature is limiting the habitats of migratory mammals, finds an international study. The researchers are calling for the creation of more open landscape areas. Elke Bunge reports.
Just two hundred years ago herds of bison could still be seen wandering through the prairies of North America. And depending on the season, lions in Southeast Asia preyed over a huge hunting area.
The world is a very different place now. Wildlife habitats have become severely limited, as urbanization, road and rail construction interrupt herd movements and trails. An international team of researchers led by the Senckenberg Nature Research Society and Goethe University Frankfurt wanted to discover to just what extent.
Outfitted with a transmitter
More than 100 scientists from leading institutes for biology, zoology and biodiversity around the world studied the movement profiles of different mammal species. A total of 803 mammals from 57 different species were equipped with a GPS transmitter in an effort to track their movements on the computer system installed in the institutes.
The results: the research team observed severe limitations in their migratory behaviour.
Human footprint reduces area of movement
Some 50 to 70 per cent of the Earth’s surface has now been altered by human intervention. Entire landscapes have been redesigned and now have a new appearance: forests have been cleared and converted into farmland, resources have been extracted from open-cast mines while the above-ground surface has been removed.
Such changes not only alter the biodiversity of the flora, but also that of the fauna. Not only have entire mammal species gone the way of extinction, but the survivors are clearly restricted in their freedom of movement.
One third less the distance
To prove this, the research team subdivided the Earth’s regions according to a grid of the human footprint, assigning them values between 0 (untouched natural areas) and 50 (dense urban cityscapes). The team also studied the movement behaviour of mammals in regions with a footprint between 0 and 35, and those above 36.
This revealed that mammals in heavily populated areas now only cover around one third the distances covered by mammals in virtually unpopulated areas. The researchers also observed a decrease in herd sizes, which they blame on a significant reduction in the availability of food.
Animals move closer to humans
Paradoxically, the researchers also discovered that some mammal species actually seek proximity to human habitation, because they are more likely to find food there. For instance, researchers at the University of Maryland found that coyotes are increasingly making a home for themselves in the periphery of Chicago.
At the same time, mammals in urban areas have only a small movement spectrum: urban design, roads and railways constrict as much as a permanent light intensity, which prevents mammals from moving freely.
Together with the narrower habitats, the researchers found a higher susceptibility to infectious diseases, because healthy mammals cannot isolate themselves from sick ones.
More open landscapes
If wild flora and fauna are to be preserved, humankind must come up with alternatives for the design of new ecosystems than existing ones.
“This is a task for future landscape designers,” said William Fagan of the University of Maryland.
The study proposes the construction of more open spaces, including corridors above or below road and rail connections. Policymakers must also ensure that wildlife habitats are preserved.
The researchers are unanimously convinced that society will soon see how important it is for the global ecosystem to find a balance between human activity and wildlife.
“It is important that animals move, because in moving they carry out important ecological functions like transporting nutrients and seeds between different areas,” said Marlee Tucker, lead author of the study and a biologist at the Senckenberg Biodiversity and Climate Research Centre and Goethe University in Frankfurt, Germany.
“If mammals move less this could alter any of these ecosystem functions.”