Galápagos Had No Indigenous Amphibians. Until Countless Numbers of Frogs Arrived
During her regular walk to the research facility, scientist Miriam San José crouches near a small pond covered by thick plants and retrieves a compact green audio device.
The device was left there overnight to capture the distinctive croaks of the Fowler's snouted treefrog, known by local scientists as an non-native species with consequences that experts are just beginning to understand.
Despite abounding with remarkable wildlife – including centuries-old giant tortoises, swimming lizards, and the famous finches that inspired Darwin's theory of evolution – the island chain near the coast of South America had long remained free of amphibians.
In the late 1990s, this shifted. Some tiny tree frogs traveled from continental the mainland to the islands, probably as hitchhikers on transport vessels.
DNA research suggest that, through time, there have been repeated unintentional introductions to the islands, and the amphibians now have a strong presence on several locations: Isabela and Santa Cruz.
The population is growing so rapidly that researchers have been finding it difficult to monitor, estimating numbers in the hundreds of thousands on each island, across developed and agricultural areas, but also in the protected natural reserve.
When San José tagged frogs and attempted to find them in the following week and a half, she could locate just one tagged frog occasionally, suggesting their populations were massive.
They calculated 6,000 frogs in a single pond. "Our estimates are still very low," states the researcher. "I am pretty sure there are even more."
Acoustic Chaos and Rising Worries
The amphibians' proliferation is evident from the acoustic chaos they cause. "The amount of frogs and the noise – it's really insane," comments the scientist.
For the researchers, their nightly vocalizations are helpful in determining their existence in remote areas, using audio devices like the one outside San José's workplace.
But local farmers say the sounds are so loud they prevent sleep at night.
"During the wet season, I regularly hear their croaks and they're extremely loud," says Jadira Larrea Saltos from the island.
"At first it was a surprise, seeing the initial frogs in the area," says the farmer, who started observing their large numbers about several years ago when one leaped on her hand as she was walking out of her front door.
Ecological Impact Stays Unknown
The sound isn't the primary problem, though. While the amphibians has been in the islands for nearly 30 years, experts still know limited information about its impact on the archipelago's precariously balanced land and water ecosystems.
On archipelagos, it is very common for non-native species to prosper, as they have none of their enemies. The islands has 1,645 invasive species, many of which are significantly disrupting the survival of its endemic ones.
A 2020 study indicates the invasive amphibians are voracious insect eaters, and might be unevenly eating uncommon bugs found exclusively on the islands, or reducing the food sources of the islands' rare avian species, affecting the food chain.
Unique Characteristics and Management Difficulties
The Galápagos frogs have exhibited some atypical characteristics, including surviving in brackish water, which is uncommon for frogs.
Their development stage is also extremely variable, with some larvae turning into frogs very quickly and others taking a long time: San José observed one which stayed as a tadpole in her laboratory for six months.
"We really don't know this part," she says, worried the tadpoles could be affecting the region's freshwater, a very limited commodity in Galápagos.
Methods to curb the amphibians in the early 2000s were mostly ineffective. Park rangers tried collecting significant quantities by hand and gradually raising the salinity of ponds in without success.
Research suggests applying coffee – which is extremely poisonous to frogs – or using electrical methods could assist, but these methods aren't always safe for other rare island species.
Without answers to more of the fundamental issues about their biology and effect, removing the amphibians might not even be the correct way to advance, says the biologist.
Funding Challenges for Research
While she expects the increasing use of eDNA methods and genetic examination will assist her team make sense of the invader, funding for the project has been hard to come by.
"Everyone wants to give support for preserving frogs," says the researcher. "But it's more difficult to find funding for an introduced frog that you might want to manage."
