At what point does wildlife health become entangled with public health and safety? The anthropocene, the current period of human activity influencing the natural environment, is far-reaching and messy as it considers how human intervention, pollution, commercialization impacts the surrounding ecosystems to reveal how human health often heavily relies on ecological levels of key populations.
A recent study in the journal Science correlates 1,3000 infant deaths in the U.S. to a population wipe-out of local insect-eating bats. Research traces the drop in bat numbers to an incurable fungal disease called white-nose syndrome. The study provides an example of how biodiversity loss affects human well-being and exemplifies the wipe-out of a keystone bat population as a case study. Eyal Frank, assistant professor at the Harris School of Public Policy and the study’s main author, highlights the tightly paired cause and effect relationship of plummeting bat numbers to an increase in agricultural insecticide use indirectly affecting human health in nearby communities. Frank establishes the first event in the domino effect as he told Newsweek “When insect-eating bat populations declined in the United States, farmers responded.”
The insect-eating bat population in North America had their first exposure to white-nose syndrome in 2006, and over the past decade, the populations across U.S. counties have collapsed as the disease caused by an invasive fungus runs rampant during their hibernation season. The fungus was traced from New York and has since spread nationally to affect bat populations in Alaska, Arizona, Florida, Hawaii, Nevada, Oregon, and Utah, most notably cash crop states, according to the United States Geological Survey. With a mortality rate of over 70% in bats, “This is essentially a death sentence for bats. Many of the affected populations are completely wiped out,” Frank said.
The mutual relationship between bat’s natural enemy intertraction to prey on crop eating pests, identifies the bats as a keystone species that served to trim the pest population and inadvertently protect the agriculture. The diminishing predation as a natural form of pesticide is then responsible for a 31.1% increase in farmer insecticide use, which the study takes further to correlate to an 8% uptick in infant mortality deaths, estimating to 1,334 additional deaths in the surrounding area.
The study’s methods isolated the correlation of infant mortality against the control group of infant mortality rates in counties that did not report a change in agricultural insecticide use. The rates in the non-affected areas, not treated by an increase in count-reported insecticide use, remained constant. The study only accounted for infant mortality deaths due to “internal cause of death”, excluding external accidents and violence.
The historical reach of pesticide use and negative impacts on the surrounding ecosystem that is internalized into wildlife and human health. The 1962 book Silent Spring by Rachel Carson documented the environmental harm caused by overuse of the pesticide DDT on wildlife and human health, terming insecticide as “biocide”. The study evaluates the detrimental health effects of insecticide despite use that is within regulatory levels.
A sister study that coincides with Frank, also published in Science, authors Ashley Larsen, Dennis Engist and Frederik Noack describe Frank’s work as “important for understanding the benefits of allocating scarce resources for biodiversity conservation.”
The follow-up study takes on an economic lens to perform a “cost-benefit” analysis to quantify the anthropogenic relationship between biodiversity loss and the economy. Compounding on health impacts, the research found that pesticides were less effective than bats at controlling pests, causing crop quality and farmers’ revenues to drop. As a result, the crop sales declined by 29%, leading to $26.9 billion in losses for farmers in counties that experienced bat die-offs between 2006 and 2017.When factoring in the health impacts, including $12.4 billion in damages from infant mortality, the total societal cost of the bat die-off amounted to $39.6 billion.
Both studies work to value the entangled relationship between wildlife populations that occupy keystone roles and ultimately the give-and-take interaction between humans and the environment. Turning to health data and the economy, the studies recognize human reliance on natural populations that strengthen local biodiversity, and promote conservation efforts to protect balanced systems.
