Environmental scientists believe that most animal groups today are facing global population declines. The magnitude of the declines is so great that many are referring to this as the beginning of the sixth mass extinction.
Amphibians are one of the most affected groups: Their estimated extinction rate since 2007 is 211 times greater than the background rate of extinction, the base rate of extinctions that would occur without human influence. Furthermore, the International Union for Conservation of Nature and Natural Resources (IUCN) estimates that 40 per cent of assessed amphibian species are threatened by extinction. In Quebec, blue-spotted and eastern red-backed salamanders, amphibians native to the province, are facing a decline even greater than the global average.
Dr. David Green, a professor in the Department of Biology, explained that scientists have long been aware of the world’s declining amphibian populations.
“The [phenomenon] of declining amphibians [was] first noticed by scientists who study amphibians 30 years ago at the end of the World’s First Congress of Herpetology,” Green said in an interview with The McGill Tribune. “It was written in Science and picked up [by] The New York Times, and that really started it off.”
While population declines are occurring across multiple animal groups, amphibians are particularly important to ecosystem health, particularly water ecosystems.
“[Amphibian larvae] help to balance the nutrients in [the aquatic] system, […] and then they transform, and they take all that material out of the ponds and […] go out on the land,” Green said.
In addition to playing a crucial role within ponds, amphibian larvae are part of land-based ecosystems. They provide an essential link between aquatic and terrestrial ecosystems and are an important food source for other animals on land.
Though scientists have been aware of amphibian population declines for decades, the causes are less clear and are still being investigated today.
“One of the major threats here and everywhere is largely habitat loss,” Green said. “That’s the elephant in the room.”
While the reasons behind these declines is not straightforward, disease may play a large role.
“The cause people are concerned with right now is diseases, particularly the chytrid fungal disease,” Green said. “Chytrid fungal infections have become nearly ubiquitous in the amphibians of the world, but this couldn’t have been possible without something causing the immune systems of the organisms to weaken.”
The amphibian immune system is unique in that its primary component is the skin. Glands under the skin of amphibians secrete compounds that attract a diverse collection of microorganisms, which serve as a strong line of defence against pathogens.
“So we have a succession of things,” Green said. “Chytrid […] is lethal as a disease. It’s also ubiquitous. You get diseased when you’re immunosuppressed. If part of your immune system is environmentally-based, […] then habitat destruction and habitat change can affect the immune system.”
Today, conservationists tackling these declines are focused on raising larvae safely before returning them to their environment, but Green is skeptical about small-scale solutions to global problems.
“It’s not a frog problem,” Green said. “It’s a people problem.”
For Green, the solution is in the way we manage global society. People should be concentrating resources in urban centres, and trying to build up instead of out.
While experts have previously been optimistic about the state of amphibian populations, Green warns that dismissing their decline as simply a warning sign is a dangerous mentality. Since amphibians occupy such a central position in their respective food webs, their loss could be more than simply a cautionary notice.
“[Amphibians] are not the canary in the coal mines,” Green said. “They are the miners.”