Article: Human Disturbance Causes Widespread Disruption of Animal Movement by Doherty and colleagues (2021)
Background: Humans have been altering the natural environment for as long as they have existed. Long before we changed the landscape through urbanization, transportation, natural resource extraction, and agriculture, human population expansions lead to the extinction of numerous species some 200,000 years ago (Boivin,et al., 2016). Humankind's effect on the natural world is so ubiquitous that Oxford researchers concluded there are no pristine, untouched places left on Earth, and there has not been for quite some time (Boivin,et al., 2016). One of the consequences of widespread human impact is that it changes the way animals move through the landscape. Some animals are forced to move farther to find food, mates, or suitable habitat, while others have a much more limited area in which they can move due to habitat loss or physical barriers, like highways or fences. It is well known that these changes can lead to decreased survival, reduced reproduction, and local extinctions; however, the extent to which human activity alters animal movement across different species had never been quantified until now.
Methods: Doherty and colleagues analyzed 719 cases of animal movement and human disturbance from 208 studies from around the world. The data included 176 species ranging from butterflies to great white sharks. Researchers grouped disturbance types into either habitat modification (e.g., agriculture, logging, and pollution) or human activity (e.g., roads, air travel, tourism, and recreation). They analyzed the data in terms of changes to a species’s home range and changes to their overall movement. A formula was used to quantify the effect of a certain disturbance by relating the undisturbed home range or movement distance to the disturbed home range or movement distance.
Findings: In the majority of cases, disturbance caused animals to increase their movement and home range size. Though some disturbances caused decreased movement, very rarely did a human disturbance cause no change in animal movement. In cases where movement increased, the average increase in movement was 70%. In cases where movement decreased, the average reduction in movement was 37%. This suggests that large changes in animal movement due to human activity are very common. Further, the movement response to disturbances varied based on animal type. Nearly all arthropods (insects, spiders, or crustaceans), birds, mammals, and reptiles increased their movement distance, while amphibians generally decreased their movement. Home range sizes of birds sometimes doubled due to disturbance, while reptile home ranges decreased by as much as 75%. With respect to disturbance type, human activity caused much stronger increases in movement than habitat modification. For example, air traffic and roads increased mammal movement by 65% and 68%, respectively, while agriculture only caused a 28% increase. However, habitat modifications resulted in significant impacts on home range sizes (e.g., agriculture and urbanization decreased mammal home range size by 27% and 49%, respectively).
Conclusions: The findings suggest that a significant and global change in animal movement is occurring that will have serious impacts on populations and increase the risk of extinction for many species. Furthermore, since animal movement is key for ecosystem processes such as pollination and seed dispersal, disruptions to animal movement can have widespread impacts. The relationships uncovered by Doherty and colleagues between disturbance types and their effects on different groups of animals will allow us to limit animal disturbances in the future. While there is no avoiding human impacts on animal movement, proper management such as maintaining wildlife corridors or banning disruptive activities in certain areas (or during certain times) will be crucial to conserving biodiversity in an increasingly unnatural world. Even small changes can have a big impact. One study found that playing a recording of a human conversation decreased mountain lion activity by 34%, resulting in cascading effects throughout the food web. So next time you go on a hike with friends, leave the bluetooth speaker at home-- you might just save a population.
Figure: Effects of disturbance on animal movement and home range size. Negative values (left of dashed line) indicate a decrease in movement or a decrease in home range size compared to being undisturbed. Positive values (right of dashed line) indicate an increase in movement or an increase in home range size compared to being undisturbed.
Reference:
Doherty, Tim S., Graeme C. Hays, and Don A. Driscoll. "Human disturbance causes widespread disruption of animal movement." Nature Ecology & Evolution (2021): 1-7.
Comments