Human-wildlife overlap is rapidly rising across the globe

As the global human population continues to grow, more than half of Earth’s land is expected to see an increasing overlap between humans and animals by 2070, according to a study conducted by researchers at the University of Michigan (U-M). 

This growing human-wildlife interaction could lead to heightened conflicts between people and animals. 

However, understanding where these overlaps will occur and which species will interact with humans is crucial for urban planners, conservationists, and countries committed to international conservation efforts. 

Populations of humans and wildlife 

Study lead author Deqiang Ma is a postdoctoral research fellow at the U-M Institute for Global Change Biology in the School for Environment and Sustainability.

“We found that the overlap between populations of humans and wildlife will increase across about 57% of the global lands, but it will decrease across only about 12% of the global lands,” noted Ma. 

“We also found that agricultural and forest areas will experience substantial increases of overlap in the future.”

What is driving the human-wildlife overlap?

The study revealed that this increasing human-wildlife overlap will be driven primarily by human population growth rather than by climate change. 

In other words, the expansion of human settlements into previously undeveloped areas will be the main driver of this overlap, rather than climate change causing animals to shift their habitats.

Neil Carter is the study’s principal investigator and an associate professor of environment and sustainability. 

“In many places around the world, more people will interact with wildlife in the coming decades and often those wildlife communities will comprise different kinds of animals than the ones that live there now,” said Carter. 

“This means that all sorts of novel interactions, good and bad, between people and wildlife will emerge in the near future.”

Calculating future human-wildlife overlap 

To calculate future human-wildlife overlap, the researchers developed an index that combined estimates of where human populations are likely to grow and the spatial distributions of 22,374 species of terrestrial amphibians, birds, mammals, and reptiles. 

The experts based their projections on previously published data that forecasted species distributions based on their climatic niches and on projections of economic development, global society, and demographics.

“The index we created showed that the majority of global lands will experience increases in human-wildlife overlap, and this increasing overlap is the result of the expansion of human population much more so than changes in species distributions caused by climate change,” Ma explained.

Major areas of concern

The researchers found that areas with high current and projected human-wildlife overlap, such as China and India, are already densely populated. 

However, they also identified forests in Africa and South America as major areas of concern due to the expected significant increase in overlap in these regions. “The reason that is concerning is because those areas have very high biodiversity that would experience greater pressure in the future,” Carter said.

The study also projected a decrease in median species richness – meaning the variety of species – in many forests across Africa and South America. 

In South America, mammal richness is projected to decline by 33%, amphibian richness by 45%, reptile richness by 40%, and bird richness by 37%. In Africa, mammal richness is expected to decline by 21%, and bird richness by 26%.

More pronounced human-wildlife interactions 

According to Carter, preserving biodiversity in these overlapping zones is vital. He noted that there are cases of human-wildlife interactions that are both good and bad, but we anticipate that they’re going to become more pronounced. 

“For example, COVID-19 was the result of human contact with wild animals, and there is concern that new diseases will emerge from greater encounters between people and certain wildlife species,” said Carter. “But you also have species that provide important benefits to people, like reducing the abundances of pests.”

Broader implications of the study 

Ma’s analysis showed that birds that consume insects in agricultural areas may decline in croplands experiencing increased human-wildlife overlap by 2070, which could affect pest control. 

“What we’re doing is finding those areas and saying, if you have cropland or pastures here, are you going to have species move into those areas or species moving away from those areas,” Carter said. 

“Are those new croplands or pastures going to be an additional threat to the species or could there be ecosystem services harnessed for free?”

Carter also highlighted the critical role of scavengers, such as vultures and hyenas, in cleaning waste from urban areas and other landscapes, which helps reduce the prevalence of diseases like rabies, anthrax, and bovine tuberculosis. 

“Hyenas and other species that are vilified or persecuted because they are scavengers provide a lot of disease reduction benefits. On one hand, they’re viewed as a threat, but on the other hand, they’re providing free health benefits,” explained Carter.

Creative conservation planning is needed

According to the researchers, conservation strategies will need to evolve, particularly in regions that have not seen significant human settlement in the past. 

Traditional conservation methods, such as establishing protected areas with restricted human access, may become increasingly difficult to implement as more areas of the world are shared by both humans and wildlife.

“There’s also a significant environmental justice argument around the validity of telling communities that may have lived in a certain area for generations that they have to move,” Carter added. 

“Our study suggests that with more areas of the world expected to be shared both by people and wildlife, conservation planning will have to get more creative and inclusive.”

Engaging local communities in conservation efforts

The researchers advocate for engaging local communities in the conservation process to build interest and improve outcomes.

This could involve establishing wildlife corridors to connect existing protected areas with new ones, creating temporary protected areas during critical wildlife periods like breeding seasons, and exploring other innovative conservation strategies.

“We care a lot about which areas can support populations of endangered species, like tigers, and how human communities interact with these species,” said Carter.

“In some places it’s going to be really hard to do everything at once: to grow crops and have urban areas and protect these species and their habitats. But if we can start planning now, we have a lot of tools to help us promote sustainable coexistence.”

The study was published in the journal Science Advances.

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