Human Activity Is Restricting Mammal Movement

Caribou were tracked with GPS as part of the study. | Tal Avgar

In areas with high levels of human activity, mammal movements can be reduced by as much as three-fold, a new study reports. The findings , published in the January 26 issue of Science, involve a diverse set of mammals across continents, highlighting the global impact of humans on wildlife.

"Previous work has focused upon single species or populations in single locations," said Marlee Tucker of Goethe University in Germany, the lead author of the study. "Our aim was to examine how human activities are impacting mammalian movements at the global scale."

She noted that restricted movement of some mammals holds implications not only for the individual animals affected, but also for whole ecosystems, if ecological interactions and the distribution of nutrients are also altered. "If mammals move less this could alter any of these ecosystem functions, such as altering the dispersal of plant seeds by animals between different habitats," she explained.

Currently 50% to 70% of the land on Earth is modified by human activities. To better understand the impact of these alterations, Tucker and her colleagues analyzed a database of movements based upon GPS tracking of 803 individual animals across 57 species. They compared the GPS data, which track individuals for varying time intervals between one hour to 10 days, to the Human Footprint Index (HFI). The HFI captures multiple indicators of human activity, including the extent of built environments, cropland, pasture land, human population density, nighttime lights, railways, roads and navigable waterways.

The researchers found that the maximum movement over a 10-day period for mammals was about 6.6 kilometers in areas with a high human footprint, compared to 21.5 kilometers in areas with a low human footprint.

Animal movement can be restricted by three-fold in areas (red) where humans have a high environmental impact. | Carla Schaffer/ AAAS

One species tracked in this study is the African forest elephant (Loxodonta africana cyclotis), which roams the Congo basin. The researchers found that an elephant living in a high human footprint area moved 22 kilometers on average over a 10-day period, while an elephant living in a low footprint area moved 44 kilometers on average over that same length of time.

Tucker explained, "This reduction in movement could be due to a combination of movement barriers, such as habitat change and fragmentation and reduced movement [related to] crops, supplemental feeding and water sources."

Reduced movement was particularly evident when animals were tracked for longer periods of time, up to 10 days, suggesting that humans are altering animals' ranging behavior and area use over longer time scales, rather than altering their travel speeds.

The researchers used computer modeling to explore how the average movement of mammals has been reduced. Their results suggest that some individuals are altering their movements to accommodate human activity, while other species with long ranges simply are not entering areas of high human activity.

So, what can humans do to minimize our impact?

"In terms of conservation, it is important to maintain landscape connectivity, such as maintaining corridors that link areas of natural habitat that enable mammals to move through the landscape," said Tucker.

"When thinking about land use planning and policy, we need to balance the needs of human activities with the needs of wildlife," she said.