Wild Mammals Reduce Their Movements In Our Presence
Humans have modified somewhere between 50-70% of Earth’s land surface, and it’s increasingly evident that this phenomenon is leading to changes in biodiversity patterns and ecosystem functions globally. This impressive joint effort by scientists from a hundred universities and research institutes worldwide offers insight into just how much the movements of mammals in areas of high human footprint differ from their usual biological patterns.
The researchers used a unique GPS-tracking database of 803 individuals across 57 mammalian species. For each observed individual, their locations were assigned a Human Footprint Index (HFI), a value combining multiple forms of human influence: the extent of built environments, crop land, pasture land, human population density, night time lights, railways, roads and navigable waterways. The allocated HFIs ranged from 0 in natural environments to 50 in high-density built environments. Other variables that are known to influence wildlife movements, such as local resource abundance, body size, and dietary guild (i.e. herbivore, omnivore or carnivore) were also included in the study.
After looking at the data, the researchers found strong negative effects of the human footprint on displacements of terrestrial mammals. In fact, the movements of individuals living in high footprint areas were shorter than displacements of individuals living in areas of low footprint by as much as three times.
Reductions in movement could be attributed to an individual-behavioral effect, where animals alter their movements relative to the human footprint. Alternatively, it could be because of a species occurrence effect, where certain species that typically exhibit long-range movement simply avoid areas of high human activity or impact. To unravel the two, additional models were run, where the HFI was split into two components: individual variability of HFI relative to the species average and the species occurrence effect.
In the end, the scientists associate the reduction of mammalian movements in high HFI areas to two main factors: movement barriers (i.e. via habitat change and fragmentation), and reduced movement requirements due to enhanced resource availability (e.g. crops, supplemental feeding and anthropogenic water sources).
The research group warns that the global nature of reduced movement across mammalian species suggests great consequences for ecosystem functioning worldwide. The effects may extend beyond to altering predator-prey interactions, nutrient cycling, and disease transmission patterns, ultimately affecting even human beings. The scientists propose that future landscape management efforts should be focused on maintaining landscape permeability by including animal movement as a key conservation metric.
Although its long-term effects are unknown as of now, movement reduction is an important issue, clearly affecting the natural behaviors of wild mammals. Animal advocates will surely benefit from expressing these findings when addressing how we should manage our impact on nature.