Herpetologists first noticed that the global frog population and other amphibian species were declining abnormally fast during the 1980s and began working tirelessly to identify the causational factors. Knowing why amphibians are dying off, and studying the unique characteristics found in those that are persevering, may give humans the key to saving these essential species.
Herpetologists specialise in the study of reptiles and amphibians. Collectively, they noticed an amphibian decline in the late 1980s and set out to document the phenomenon. The effort culminated in a worldwide survey of amphibian populations published in 2004. According to the report, nearly one-third of amphibian species are at risk of extinction. More studies followed, finding that in the United States, amphibian populations are declining at an average rate of 3.7% per year. Notably, the decline was found in all populations, not just those considered endangered, including those found mainly in conservation areas.
Why are Amphibian Species in Decline?
Amphibians include frogs, toads, salamanders, and newts. They have permeable skin and live in aquatic and terrestrial habitats throughout their lifecycle. As a result, they are more vulnerable to environmental threats than other species facing population decline, like birds. Amphibians have existed on Earth for about 400 million years despite their apparent delicacy, surviving the extinction of the dinosaurs, the Industrial Revolution, and many other global changes. Their rapid disappearance today however, suggests that the rate of change in the 21st century exceeds anything they have faced in the past. Researchers concluded in a 2011 report on the role of cofactors in amphibian decline that “modern selection pressures, especially those associated with human activity, may be too severe and may have arisen too rapidly for amphibians to evolve adaptations to overcome them.”
To put it more simply, scientists have not isolated one cause of the amphibian population decline. Rather, several reasons have been implicated, and experts believe it is likely that a complex, interrelated combination of factors is responsible, including:
1. Human Exploitation
The exotic wildlife and animal trade is fuelled by the demand for amphibians as food, medicine, and exotic pets. Nearly half of amphibians available online or in pet stores were collected in the wild. According to a study published in 2021, data showed evidence of trade in at least 1,215 amphibian species, approximately 17% of all amphibians. Of these species, more than one in five are considered vulnerable, endangered, or critically endangered. After analysing the origins of traded individuals, they found that a staggering 42% of which came from the wild.
2. Pesticides & Toxins
The widespread use of pesticides, pollutants, and other synthetic chemicals impact amphibians severely. While all species, including humans, are harmed by exposure to pollutants, amphibians are especially susceptible due to their permeable skin.
3. Invasive Species
Humans are responsible for introducing alien species to habitats worldwide. Whether it is intentional – to combat a pest species or when an exotic pet is released into the wild – or unintentional – when organisms stow away on a boat or plane – the impact on the native species is the same. A native amphibian may be preyed upon by an alien one or forced to compete for resources against an unknown foe.
A single disease, Batrachochytrium dendrobatidis, known as the chytrid fungus, is considered one of the biggest threats to amphibians worldwide. An incredibly infectious disease known to infect every amphibian species, the infection attacks the frog’s skin, eventually causing heart failure.
5. Habitat Destruction
Amphibians have been devastated by humans’ alteration and destruction of their natural habitats. Most species require aquatic and terrestrial ecosystems during their life cycle; they are doubly impacted. Actions like draining wetlands for residential or agricultural development have drastically reduced the range of habitat available to amphibians.
6. Climate Change
Changes in precipitation patterns caused by climate change alter wetland habitats, threatening amphibian populations. Another amphibian habitat is lost for every vernal pool, pond, or wetland that is struck by drought and dries up for good.
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How Does the Loss of Amphibian Species Impact Humans
Salamanders, newts, toads, and frogs are all part of the human experience for those who grew up in rural or suburban areas. The emergence of frogspawn (frogs eggs) and tadpoles signals the beginning of spring. Catching the adults is a common childhood pastime. Frog calls outside the window lull people to sleep each spring, and are recorded and played through headphones to the same effect. Their mating serenades are the soundtrack to a thousand movies and a million human experiences. Though small and often shy, amphibians represent a quintessential part of nature.
The influential role of frogs in human lives is evidenced by their appearance as characters in mythology and folklore dating back thousands of years. From one of the ten plagues of Egypt to the Grimm Brothers Frog Prince to Kermit the Frog, amphibians have been represented prolifically in human civilisation throughout history. Frogs were featured twice over, as a character in stories and the critical ingredient in classic dishes. Their legs are considered a delicacy by the French and North Americans.
While only the legs are consumed, the entire frog is considered vital to research. Amphibians’ secretions have been used in traditional remedies for millennia, and scientists believe that the chemicals may hold the key to invaluable scientific advancements. As subjects, amphibians are favoured for their well-understood physiology, relative similarity to humans, and species diversity. They are used to learn about musculoskeletal, reproductive, and other bodily systems, playing a prominent role in understanding environmental endocrine disruptors.
On a larger scale, amphibians represent a significant percentage of living creatures on the planet. Their role in ecosystem services cannot be overstated. Many ecological communities rely on these keystone species, the linchpin that other organisms largely depend upon. Removing an amphibian population changes an environment drastically through small, profound changes. Furthermore, characterised by their delicate skin, vulnerability to non-native predators, and reliance on not one but two types of habitat throughout their lifecycle, amphibians are considered an indicator species. Sensitive to changes in their habitat, they act as a measure of the environment’s health in a given locale. Consequently, their declining numbers might indicate greater global implications.
Amphibians Decline Signals that Change is Needed to Ensure Survival
While it is undoubtedly too late for some declining species, others may have a chance. While one species dies out, another may be thriving, teaching a critical lesson about the characteristics or circumstances promoting survival. Learning from amphibians is imperative; understanding the factors causing the decline may reveal the key to halting it. Moreover, taking action by incentivising renewable energy use, combating the exotic animal trade, banning pesticides and herbicides, and more is a step toward saving amphibians and ourselves.
Humans may be less sensitive than amphibians, but it is undeniable that the factors driving their decline already impact human health. If allowed to continue, they will eventually compromise the survival of the human species. By studying the decline of amphibians, acknowledging it as a warning signal, and reacting, humanity is given a chance to act before it is too late.
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