A growing body of research links environmental disturbance and biodiversity loss to human diseases, including those, like Covid-19, that are caused by viruses jumping from animals to people.


Cleared forest land in Brazil

For several years scientists have warned of an impending sixth mass extinction of species on Earth. A 2019 analysis showed North America had lost more than one in four birds since 1970. Now, research suggests that ecosystems the size of the Amazon forests and Caribbean coral reefs could collapse much faster than previously expected.

A team of scientists examined data on transformations of 40 natural environments on land and in water. Their work showed that while larger ecosystems took longer to collapse due to sheer size, they transformed at significantly faster rates than smaller systems.

Stress can cause ecosystems to change quickly. Larger ecosystems contain multiple sub-systems of species and habitats, a structure that provides initial resilience against stress. But at a certain threshold, these sub-systems accelerate the rate at which an ecosystem unravels. Without significant relief from stress, Amazon forest ecosystems could collapse in 49 years and Caribbean coral reefs in only 15.

Both ecosystems currently experience significant stress. As previously reported in Texas Climate News, roughly 20 percent of the Amazon is already deforested, and in 2018 the planet as a whole lost some 30 million acres of tropical forest, almost 9 million acres old-growth or primary forest. Such losses exacerbate climate change; old growth forests store more carbon than other types, and the world’s forests together store 40 percent more carbon than what resides in fossil fuel deposits. Amazon deforestation alone accounted for 1.5 percent of the increase in atmospheric levels of carbon dioxide since the mid-19th century. Ultimately, deforestation in the Amazon means hotter temperatures in Texas.

Sources of stress for global coral reefs include overfishing, pollution, physical destruction and climate change. One effect of climate change is coral bleaching, and significant bleaching events are occurring with greater frequency. An event from June 2014 to May 2017, which affected reefs at the Flower Garden Banks National Marine Sanctuary off the Texas coast, was the longest, most widespread and most damaging on record – so far.

Currently, the National Oceanic and Atmospheric Administration’s Coral Reef Watch predicts high levels of heat stress that can cause bleaching across a wide area through July 2020. Recently, the Great Barrier Reef Marine Park Authority announced severe mass bleaching of Australia’s iconic reef in the current summer season (2019-2020). A study TCN covered in fall 2019 showed that severe heat waves can kill corals outright in addition to damage they experience from bleaching.

Coral reef loss, too, affects Texas. Reefs provide $2 trillion per year globally in ecosystem services, including supporting commercial and recreational fishing and tourism industries, all three significant parts of the state’s economy.

Escalating impacts

Bottom line, people must prepare for faster-than-ever changes in the planet’s ecosystems and ever greater consequences of those changes – including disease outbreaks such as the current Covid-19 pandemic. A 2010 paper in Nature reported that a growing body of evidence connects increased disease transmission and biodiversity loss. West Nile encephalitis, for example, is caused by a virus transmitted by mosquitos with several species of birds acting as hosts, and studies found strong correlations between low bird diversity and increased incidence of West Nile in the United States.

Human-caused environmental disruption has been linked to a series of zoonotic diseases (those caused by pathogens transmitted between humans and animals, particularly wild animals), including SARS in 2002, MERS in 2012, H1N1 or swine flu, and Ebola. A 2008 paper in Nature reported that the majority of emerging infectious diseases were caused by zoonotic pathogens, with more than 71 percent of those caused by pathogens originating in wildlife.

According to Jonathan Epstein, a disease ecologist at EcoHealth Alliance, the majority of emerging zoonotic diseases also can be linked to human activities. “As the human population grows and demand for animal protein grows, we’re expanding our farming systems often with poor barriers separating wild and domestic animals,” he told Texas Climate News. “Anything we do to change the environment around us that increases our contact with wildlife also increases our risk of encountering known and unknown viruses.”

Epstein’s organization looked at activities that drive emerging disease hotspots around the world and found that one of the most significant was land-use change. Clearing forest for agriculture or urban development and even reforestation cause changes in the structure of wildlife communities and the ways people come into contact with animals and any pathogens they may carry. Further, in disrupted ecosystems viruses may need new hosts, and people provide a convenient target. Risk of Lyme disease, for example, increases where suburbs fragment forests, making it more likely that a tick carrying Lyme bacteria can bite a human.

“We need to recognize that human outbreaks are directly related to environmental integrity,” Epstein said. “The increased risk of disease outbreaks should be built into assessments of whether we should clear a patch of forest or build infrastructure.”

A few years ago, for example, a developer wanted to build a residential community near Bracken Cave in Central Texas, summer home to more than 15 million bats. “We worked with the city of San Antonio to assess whether there was a health risk of building homes right next to the largest population of bats in the world, and there was, in addition to the huge conservation consequences for the bats,” he said. “That’s an example of the kind of thinking we have to have.” Ultimately, the land instead was purchased by Bat Conservation International, which already owned the cave’s location.

Additional factors contributing to disease outbreaks include the often-illegal capture and transport of live wild animals and their handling and consumption. In addition, human-caused climate change is creating conditions that increase the spread of mosquito-borne diseases such as West Nile virus, malaria, and dengue fever.

On the other hand, according to a paper published in the journal Nature in 2010, biodiversity itself seems to protect organisms, including humans, from transmission of infectious diseases. As the saying goes, nature doesn’t need us, we need nature. We continue to mistreat her at our own peril.


Related coverage by Texas Climate News:

Climate change and globalization driving tropical diseases toward Texas

Texas is a ‘hot zone’ for diseases borne by mosquitoes, ticks and fleas

Amid worrisome Zika news, longer mosquito season found across the U.S.


Melissa Gaskill is a contributing editor of Texas Climate News.

Image credit: Miguel Pinheiro / Center for International Forestry Research via Flickr