22,374 species at risk as humans to expand into 50% of Earth’s land by 2070

As the human population grows, more than half of Earth’s land will experience an increasing overlap between humans and animals by 2070, according to a University of Michigan study.

The U-M researchers say that greater human-wildlife overlap could lead to more conflict between people and animals.

“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. We also found that agricultural and forest areas will experience substantial increases of overlap in the future,” said Deqiang Ma, lead author of the study and a postdoctoral research fellow at the U-M Institute for Global Change Biology in the School for Environment and Sustainability.

Human-wildlife overlap

The study showed that the human-wildlife overlap will be driven by human population growth rather than climate change.

Increasing the number of people settling in previously undeveloped areas will drive the overlap rather than climate change, causing animals to shift where they live.

“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 Neil Carter, principal investigator of the study and associate professor of environment and sustainability.

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

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

They drew information about the spatial distribution of vertebrates from previously published data that forecasts where species will live based on their climatic niches.

Their estimates of where people are likely to live were based on economic development projections, 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 said.

Specifically, the researchers found that areas that currently have and are projected to have high human-wildlife overlap in 2015 and 2070 are concentrated in regions with high human population density, including China and India.

In addition to those places where the overlap is already high, “another area of major concern are forests, particularly in forests in Africa and South America where we’re seeing a large increase in the overlap in the future,” Carter said.

“The reason that is concerning is because those areas have very high biodiversity that would experience greater pressure in the future.”

The researchers also found that median species richness—the variety of species in a given area—is projected to decrease across most forests in 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 projected to decline by 21% and bird richness by 26%.

Pandemic rise

Preserving biodiversity in these zones of overlap has real benefits, Carter said.

“There are cases of human-wildlife interactions that are both good and bad, but we anticipate that they will become more pronounced.

For example, COVID-19 resulted from human contact with wild animals, and there is concern that new diseases will emerge from greater encounters between people and certain wildlife species,” he said.

“But you also have species that provide important benefits to people, like reducing the abundances of pests.”

According to the researchers, future conservation strategies will have to evolve, especially in regions that have not previously seen much human settlement.

In the past, a core conservation strategy was to establish protected areas where human access was restricted. However, this is becoming harder to implement because there are fewer such places.