Frogs are some of the most unique and diverse species on the planet. There are currently over 7,500 known species, with new frogs being discovered all the time. Just this year, three new frogs were discovered by scientists deep in the eastern rainforests of Madagascar. Unlike their pond-dwelling cousins, these tiny frogs spend their entire lives in pandan trees, relying on rain water that catches in the leaves.
This recent discovery is a great example of how these incredible frogs have evolved over thousands of years to survive in almost any natural condition. Yet despite this resilience, 41% of amphibians are globally threatened with extinction. In this blog, we will discuss why the world’s frogs are under threat, what the consequences are, and how frogs are an indicator species that indirectly supports all life on earth.
Frogs exist in almost every corner of the planet. They can be found in lush rainforests, frozen tundras, deserts, and even your own backyard. Some frogs are so unique that their appearance and behaviors sound like they have been ripped straight from the pages of a science fiction novel.
Take the hairy frog (Trichobatrachus robustus), which is able to break the bones in its toes and force them through the skin to create sharp claws, allowing it to inflict injury and escape from potential threats. This neat little trick has earned them the nickname ‘horror frog.’ The wood frog (Lithobates sylvaticus) is the only frog that lives north of the Arctic Circle, and survives by freezing solid during winter and thawing in again when spring arrives. Some frogs, including the infamous dart frog subspecies (Dendrobates) found in the tropical forests of Central and South America, are so venomous that they can kill a grown man in under 10 minutes. As we can see from these few examples alone, frogs are a complex and bizarre species.
In general frogs have webbed feet, bulging eyes, no tail, and smooth, moist skin. They are amphibians, which means they are cold-blooded and have spines but no scales. They can live on both land and in water, making them adaptable to a number of different environments. While frogs and toads look pretty similar, there are a few ways to tell them apart. Toads tend to spend more of their time on dry land. Most significantly, they have warty, rough skin which is how most scientists distinguish them from frogs. Toads also have shorter legs, which they use to crawl around rather than hop. They are slower and less active than frogs. Other amphibians such as newts and salamanders are easier to tell apart due to their elongated bodies.
Frogs primarily survive on a diet of insects, such as flies, mosquitos, moths, and dragonflies. They are also known to eat snails, slugs, worms, and spiders. Aquatic frog species, which live most of their lives underwater, feed on small crustaceans, larvae, worms, and crabs. Frogs are the definition of a generalist predator, eating just about anything that comes their way—including other frogs and amphibians! They use their long, sticky tongues to snatch unsuspecting prey as it passes by, making them quite skilled hunters.
While frogs eat almost anything, a lot of animals also eat frogs. This has forced the species to evolve some incredible ways to evade and incapacitate predators. Of course, some frogs are incredibly poisonous, but others—like the glass frog—have adapted to become almost completely transparent, making them partly invisible!
As mentioned, frogs are found all over the world, even in regions where you can’t imagine much life surviving at all. Most frogs need a source of freshwater, and therefore will more often be found in aquatic and swampy habitats. Without water, most frogs can only live between three and nine days. That said, there are exceptions. Take the Australian Turtle frog (Myobatrachus gouldii). Named for its turtle-like shape, this bizarre animal found on the west coast of Australia lives almost exclusively in sandy soils, and can survive without any free standing water. Even more strange than that, this frog is one of the few that skips the tadpole stage, and instead lays eggs which hatch into tiny froglets.
Brazil is home to the most diversity of frog species. Peru, Columbia, Ecuador, and many other South and Central American countries also boast hundreds of unique frog types. This is because the region, which includes the mighty Amazon rainforest, is a biodiversity hotspot providing some of the best conditions for frogs to inhabit.
How long frogs can live for is generally unknown. Tropical leaf frogs have been known to only live one or two years, while other species like the giant goliath frog (Conraua goliath) have been known to live up to 15 years in the wild, and over 20 years in captivity.
So why are there so many varied and unique frog species in the world? The dominant theory is that frogs are able to adapt based on opportunity, such as finding some new ways of exploiting a natural resource where there’s little competition (such as food and shelter). The species can then evolve to become an expert in that resource. An example would be the aforementioned turtle frog which has evolved to survive in dry and warm environments.
However, this doesn’t completely explain the incredible patterns and colors some frogs exhibit, especially those that inhabit the same ecosystem. For example, a single species of poison dart frog found in Peru has 10 different pattern variations, which provide a warning for predators to stay away. Evolutionary biologist Mathieu Chouteau set out to find out why.
The biologist created 3600 frog models, all 18 millimeters long. Each one was yellow striped or reticulated, like a giraffe, with green lines. The models were then placed in two different sites: one in the Amazonian lowland of Peru and the other in a valley at about 500 meters above sea level. What Chouteau observed after several days was that birds mostly avoided the model with the pattern that looked like the local frog, but they attacked the model that looked unfamiliar. The phenomenon was reversed at the other site.
This experiment highlighted two things. First, once diversity in an area is established, it stabilizes. Even a new pattern of poisonous dart frog causes disruption, no matter how brightly colored and off-putting. Secondly, the reason the frogs are different is likely down to genetic drift—just random gene variations that keep evolving to create different patterns among a localized group. This random genetic variance makes them distinctive from another group of the same species somewhere else.
The life cycle of a frog is incredibly interesting, as they go through something called metamorphosis. Metamorphosis means that frogs experience several distinct physical changes in their journey from egg to full grown frog. Insects like butterflies and some fish also experience such incredible changes in their lifecycle.
Frogs begin life as an egg, also known as frog spawn. These eggs look like a tiny black dot surrounded by a protective jelly, which helps the egg absorb impact as it floats around in ponds and rivers. Some species of frog can lay up to 4000 eggs at one time, which means large clumps of eggs are quite easy to spot if you’re looking for them. Despite their protective jelly, the eggs are still incredibly delicate. Only around 1 in 50 of these eggs will survive until adulthood.
The surrounding jelly also provides food for the developing tadpole, insulating them from the elements, and protecting them from diseases that may harm the embryo. Before the frogs hatch into tadpoles, a small tail develops inside the egg. Once they are ready, the tadpole uses its new found strength to break free from the egg and jelly sack and enter the ecosystem. This stage can last anywhere from 3 days to 25 days.
For the first few days of a tadpole’s life, they are incredibly soft and vulnerable and will hang out exclusively around water plants and grass. They feed on particles of vegetation that filter through the water. Tadpoles develop gills and legs fairly early on which lets them breathe underwater and swim around hunting for food in their comma-shaped state. Tadpoles play an important role in maintaining water quality by keeping algae spread under control. Without the tadpoles, excess algae could lead to harmful blooms that deplete oxygen and harm aquatic life.
During this stage, the tiny tadpoles will experience a number of internal and external changes. Hind legs will begin to appear and their tails will elongate. They will also start to develop lungs which will allow them to leave the water. Once their lungs start working, a layer of skin will grow over their tadpole gills.
One of the most amazing things about tadpoles is that they can actually control their rate of transformation! In situations where they feel threatened, from predators or environmental pressures, the tadpoles can actually speed up their metamorphosis so they can hop out the water and escape. They can also slow down the changes for up to a year if temperatures are too cold, for example. This is a prime example of how dramatic changes in our atmosphere due to climate change can deeply impact frog development.
The final development from a tiny froglet into an adult frog can take around four years to complete. By this stage the frogs don’t need to rely on water quite so much, and adult female frogs will begin to search for a mate to repeat the process all over again. Male adult frogs will croak loudly and make a lot of noise to attract the perfect partner. Like whales, each frog species will sound different so that their female counterparts can distinguish between the calls.
Without a doubt, frogs are some of the world’s most important creatures. They occupy a critical position in the food chain, serving as both predator and prey to a huge variety of species. As predators, they are nature’s pest control, keeping insect populations in check. As prey, they provide nutrients and sustain the populations of other larger reptiles, birds, and fish. Frogs are also considered an indicator species, because they are very sensitive to environmental changes. Their population health reflects the overall condition of their ecosystem, which offers scientists early warning of environmental degradation, pollution, and climate change.
As well as playing a critical role in ecology, frogs have enormous medical importance. It might not seem like it, but a lot of today’s cutting edge medical discoveries are taking place because of frogs. For example, stem cell research was made possible by John Gurdon's work cloning frogs. The eggs he created grew into new tadpoles which proved the theory that mature cells (like the one in the original tadpole) still contained all the necessary information to grow an organism from scratch.
In another experiment, researchers at the Allen Discovery Center at Tufts University were able to help blind tadpoles see by grafting eyes onto their tails. More than simply helping tadpoles’ gain vision, the experiment was designed to test how electrical signals could be adjusted to encourage the body to accept a new anatomy—such as organ transplants in humans. These are just two examples, but for the last sixty years frogs have provided crucial insights into human vertebrate development, cell biology, and genetics.
Hypothetically, let’s pretend all frogs vanished from the Earth. What would that look like? What would happen?
If all frogs disappeared, chaos would quickly ensue. The first thing that you would notice is that insects—a frog’s primary food source—would explode in numbers, overwhelming crops and spreading diseases like malaria, dengue fever, and West Nile virus which are transmitted by insects. This could also lead to the population decline of their primary predators, or force them to find alternative food sources, which could cause biological cascades that ripple out into other ecosystems, disrupting nature’s delicate balance in a huge way. Farmers would need to rely more on pesticides to keep the bugs at bay, resulting in a contaminated food chain, health problems, pesticide-resistant insect strains.
When frogs begin to vanish, it’s a sign that something is wrong. When pollution or climate change begin to affect an area, frogs are the first casualties, providing an early warning sign for endangered ecosystems. This is why it’s so alarming that 41% of the world’s amphibians are threatened with extinction—that’s two in every five species! In Sri Lanka, of the 111 known amphibians that live in this tropical island country, 18 are listed as extinct, 11 of which were last recorded in the late 1880s. In some regions, specifically South and Central America, more than 100 species are threatened. So what’s going on?
According to the IUCN Red List paper outlining the State of the World’s Amphibians, 93% of the world’s 2893 threatened amphibian species are so because of habitat loss. As human populations have exploded in the last 200 years, demand for land and resources has increased dramatically. Land is cleared for timber and mining. Agricultural expansion, including crop cultivation and cattle ranching, remain the number one driver of forest degradation. Urban expansion has also replaced key amphibian habitats. Any remaining habitats are often too small or degraded to support a healthy and viable population, or are too far apart for frogs and other amphibians to travel safely.
Changes in the earth’s atmosphere directly impact frog populations, because the majority are highly reliant on water to survive. Their moist and permeable skin makes them particularly sensitive to changes in temperature and humidity. Climate change exacerbates and fuels severe weather, storms, flooding, drought, and temperature extremes. Even in regions where amphibians have adapted to extreme weather, like in the Caribbean Islands, increased frequency and impact impede the species ability to recover. Often amphibians will try to migrate to cooler environments, but those in harder to reach environments will be trapped with nowhere to go.
Research into the tiny tropical puddle frog proved that environmental variation drives genetic diversity, reducing vulnerability to climate change. Protecting these ‘habitat hotspots’ may help more species adapt to changing conditions. This research underscores the need for conservation efforts focused on habitats that foster genetic variation.
In Panama, the once abundant harlequin toad has experienced catastrophic declines linked to chytridiomycosis, an infectious disease that has impacted about 30% of the world's amphibians. Between the 1980s to today, the disease has spread across Australia, Mexico, and the Andes of South America. It’s currently making its way across Africa. The disease has been directly linked to 9 of the 11 extinctions since the 1980s. There is still no cure.
There are signs, however, that amphibians have been recovering. At least 60 species that were once declining, possibly due to chytridiomycosis, have moved to a lower extinction risk category, in some cases developing natural immunity to the disease. Despite this small piece of good news, many, many species are still at risk, which highlights the importance of restoring and protecting biodiverse amphibian habitats.
It’s important to note that the true number of threatened amphibians is still unknown, as there is insufficient data available to assess their extinction risk. The reasons for this are diverse, and include lack of trained herpetologists (amphibian scientist) in certain areas, few species observations, out-of-date records, unknown threats, and unknown population status. However, more research is being conducted in India, Peru, and China for example, as new species have been discovered.
This is the reason why Plant Wild went to Ecuador to work with Centro Jambatu (the Ark of the Frogs). This team ventures deep into the cloud forests of South America to search for ‘lost frogs’—amphibians who haven’t been seen in decades and are listed as ‘possibly extinct.’ This work helps gather vital data on the state of frog populations in biodiversity hotspots like Ecuador, allowing scientists to grow and support endangered populations that are so integral to ecosystem health.
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