Biodiversity and Health Extinction by Infection: Biodiversity makes a difference.
An important topic that emerged during Sustaining Life, Securing Our Future, a daylong symposium by CERC, concerned the role of biodiversity in reducing the affect of viruses and other pathogens on populations of special concern. Throughout the past several decades, countless species have been infected by non-native deadly diseases and ultimately crashed in numbers. Analyses on the Honeycreeper birds of Hawaii and the hibernating bats in the North Eastern United States help us further understand the fragility of the environment in light of pervasive diseases.
Residing throughout the environmentally diverse islands of the Hawaiian archipelago for many centuries, the Honeycreepers are a remarkable group of birds. Diversifying from a single colonization into 20 genera and more than 50 species, each morph has its own behavior, morphology, and physiology, well adapted for the unique niches in which it occupies. Despite the historical success of the Honeycreeper, 17 are now thought to be extinct and 14 more are endangered. According to a study by the United States Geological Survey (USGS), “…it is clear that the abundance, diversity, and geographic distribution of Hawaii’s native birds changed significantly after the arrival of mosquitoes, avian malaria, and poxvirus.” With no natural resistance against these highly virulent pathogens and the unique climatic and ecological conditions of the islands, these epizootics were able to spread at extremely high transmission rates. The honeycreepers in Hawaii significantly declined in numbers and their geographic range shrunk. Given increasing global mean surface temperatures, high-elevation disease refuges, well suited to the life of Honeycreeper, will disappear, and further exacerbate the problem. Providing an outline for prospects of intervention, the authors conclude the report by stating that the honeycreepers’ “…survival into the next century may ultimately depend on our ability to remove or mitigate introduced threats…”
In 2006, bats living in caves all across the North Eastern United States started behaving strange. They were found awake during the day and flying during the wintertime, awaking from hibernation far too early. As a result, they lost precious fat reserves and ultimately started to die. It was soon discovered that White Nose Syndrome, aptly named for a cold-living fungus (Geomyces destructans) found on the nose, wings, ears and exposed skin tissues of infected bats. Thus far, 9 hibernating bat species have been confirmed to have the dangerous infection; 5 have already experienced serious mortality. According to a study by the United States Fish and Wildlife Service, there has been a “90 to 100 percent mortality of bats (primarily little brown bats) at several hibernacula in New York, Massachusetts, Connecticut and Vermont.” As pollinators of plants and disperses of seeds, worries exist over the future of crops in those areas affected, once again reminding us of the fragile balance of nature.
These case studies highlight the importance of mitigating the virulence of the planet’s pathogens. Though intervention and conservation efforts are critical once these viruses have spread, preventive measures may hold the most crucial promise. One way in which we can prevent the transmission rates of viruses is by preserving the biological diversity of communities. A recent study reported that an increase in avian diversity is largely correlated with a decrease in the spread of West Nile Virus in humans. This phenomenon, in which biodiversity and rates of disease transmission are linked, is known as dilution effect. Though debate exists over the exact mechanisms, scientists believe that environments that have high indices of biological diversity also have a lower proportion of suitable hosts for a disease, thus reducing the likelihood of transmission. Supporting this finding, an article in Nature released in 2010 announced similar results: “Overall, despite many remaining questions, current evidence indicates that preserving intact ecosystems and their endemic biodiversity should generally reduce the prevalence of infectious diseases.”