Humans force mammals to cover shorter distances
Whether it be the zebras in the Savannah, rabbits on the field or tree-dwelling monkeys - terrestrial mammals are on the move on a daily basis and they cover shorter or longer distances, e.g. in search of food. They tend to cover shorter distances in areas with a higher human footprint. An international team of researchers that include Claudia Fichtel and Peter Kappeler from the German Primate Center (DPZ) conducted a comprehensive study and concluded that the average distance covered by the animals is up to three times shorter. For this, the scientists analyzed the GPS data of 57 different mammal species. The authors point out that this development could have far-reaching consequences for the ecosystems and ultimately for humans (Science).
As the team of scientists led by biologist Marlee Tucker, Senckenberg Biodiversity and Climate Research Centre and Goethe University Frankfurt, has shown, the range of action of mammals in areas strongly influenced by humans is significantly reduced. In the most comprehensive worldwide study to date on this topic, Tucker and 114 co-authors have evaluated the movements of 803 individuals. "We examined a total of 57 mammal species that included for example rabbits, wild boars, elephants and non-human primates. The researchers in the team equipped each animal with a GPS transmitter, which enabled us to track their whereabouts for at least two months," says Tucker.
Peter Kappeler and Claudia Fichtel, scientists in the Behavioral Ecology and Sociobiology Unit of the DPZ, contributed the GPS data of two lemur species from Madagascar - eight sifaka and four red-fronted lemur groups - to the study. Behavioral research has been conducted on lemurs for more than 20 years at the DPZ field station in the Kirindy forest on the west coast of the island.
All data from the worldwide locations of the researchers were finally combined in the "Movebank" portal, which archives the animal movements. The scientists compared the data with the Human Footprint Index of the areas in which the animals moved. This value is an indication of the changes brought about by humans, for example through the construction of settlements, transport routes or agriculture. In areas with a comparatively high Human Footprint Index, for example, a typical German farming area, the mammals in the area covered in ten days on average of only 33 to 50 percent of the distance that mammals in pristine nature cover. This applies both to the maximum distance traveled in ten days and the average distance covered over this period.
It is possible that mammals cover shorter distances because they have adapted to areas with a high human footprint. In some of these areas, a better food supply is sometimes available and therefore animals do not have to cover longer distances to feed themselves. In addition, roads and the fragmentation of habitats in many places limit the movement of animals.
"Our research area in Madagascar has an average Human Footprint Index of 21," says Claudia Fichtel. "The lemurs investigated at our station still live in an almost intact forest, but this is also extensively deforested. In other places in Madagascar, people's influence is even more serious. The destruction caused to their habitat is the reason why so many lemur species are threatened in Madagascar."
The researchers are worried that the shorter distances covered by the animals, could have a significant effect on the ecosystem functions linked to animal migration. "It is important for animals to cover certain distances in order to transport nutrients and seeds between different areas. In addition, many natural food webs are based on animal movements. Last but not least, disease transmissions depend on animal movements. As animals move less, many of these processes can change in ecosystems," says Tucker.
Original publication
Tucker, M.A. et al. (2018): Moving in the Anthropocene: Global reductions in terrestrial mammalian movements. Science, DOI: 10.1126/science.aam9712