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
, published in the January 26 issue of Science, involve a diverse
set of mammals across continents, highlighting the global impact of humans
"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
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.