The Galápagos Islands Lacked Any Native Amphibians. Then Countless Numbers of Amphibians Arrived

On her daily commute to the scientific station, scientist the researcher crouches near a small water body surrounded by thick vegetation and collects a small plastic audio recorder.

She had placed there through the night to record the characteristic calls of the Fowler's snouted treefrog, recognized by local researchers as an invasive species with effects that scientists are starting to understand.

Despite abounding with unique wildlife – such as ancient giant tortoises, marine iguanas, and the well-known finches that sparked Darwin's theory of evolution – the Galápagos archipelago near the shoreline of Ecuador had historically been devoid of amphibians.

In the late 1990s, this shifted. Some tiny amphibians traveled from continental the mainland to the archipelago, likely as hitchhikers on transport vessels.

Genetic research suggest that, through time, there have been repeated unintentional introductions to the archipelago, and the amphibians now have a firm foothold on several locations: multiple locations.

The population is growing so rapidly that scientists have been finding it difficult to monitor, estimating populations in the hundreds of thousands on each island, across urban and farming areas, but also in the protected Galápagos national park.

When San José marked amphibians and attempted to find them in the following week and a half, she could locate just one marked frog occasionally, suggesting their populations were massive.

They calculated 6,000 frogs in a single pond. "The calculations are still very low," states San José. "I am pretty sure there are additional numbers."

Deafening Noise and Rising Worries

The frogs' abundance is evident from the sound chaos they create. "The number of frogs and the noise – it's really incredible," comments the scientist.

For the researchers, their nocturnal vocalizations are useful in determining their presence in far-flung areas, using audio devices like the one outside San José's office.

But nearby farmers say the calls are so loud they prevent sleep at night.

"During the rainy period, I regularly hear their calls and they're really loud," says Jadira Larrea Saltos from the island.

"Initially it was a shock, observing the initial frogs in the region," says the farmer, who started observing their abundance about three years ago when one leaped on her palm as she was walking out of her house.

Environmental Consequences Stays Unclear

The sound isn't the primary problem, though. While the amphibians has been in the Galápagos for almost three decades, scientists still know very little about its effect on the islands' delicately balanced land and water ecosystems.

On archipelagos, it is very common for invasive species to prosper, as they have none of their enemies. The Galápagos has over sixteen hundred invasive types, many of which are significantly disrupting the survival of its endemic ones.

A 2020 research suggests the non-native frogs are hungry insect eaters, and might be unevenly eating rare bugs found only on the islands, or reducing the nutrition of the region's uncommon birds, affecting the ecosystem balance.

Unique Characteristics and Control Challenges

The island frogs have exhibited some atypical traits, including living in brackish water, which is rare for amphibians.

Their metamorphosis stage is also extremely inconsistent, with some tadpoles turning into frogs very rapidly and others taking a extended period: San José witnessed one which stayed as a tadpole in her laboratory for half a year.

"We really don't know this part," she says, concerned the larvae could be affecting the islands' freshwater, a very scarce commodity in Galápagos.

Techniques to curb the amphibians in the early 2000s were mostly unsuccessful. Conservation officers tried collecting large numbers by hand and slowly increasing the salt content of lagoons in vain.

Research suggests applying coffee – which is highly toxic to frogs – or using electrical methods could help, but these approaches aren't always safe for other rare Galápagos species.

Lacking answers to more of the fundamental questions about their lifestyle and effect, removing the frogs might not even be the correct way to proceed, says San José.

Funding Challenges for Study

While she hopes the increasing use of eDNA methods and genetic analysis will assist her group make sense of the invasive species, funding for the project has been hard to come by.

"Everyone wants to give support for protecting frogs," says San José. "But it's more difficult to find funding for an introduced frog that you might want to manage."