Non-native frogs hitch to Galapagos Islands

The non-native tree frog called, Scinax quinquefasciata, was first sighted in the Galapagos Islands in 1998.

July 7, 1999
Web posted at: 8:21 a.m. EDT (1221 GMT)

Due to their intolerance of salt water, amphibians have generally been absent from the Galapagos Islands for the past several million years, researchers say. Historically only fish, reptiles, birds and mammals have been present in the remote oceanic archipelago. But recent human activity and climate change may have combined to alter the situation and frogs are now one of many non-native species found in the Galapagos.

Reproducing populations of frogs have become established on at least two of the five populated Galapagos Islands. According to scientists at the Charles Darwin Research Station, growing human activity in the Galapagos Islands has led to the importation of large amounts of material from continental Ecuador, allowing frogs to hitch a ride on cargo ships or airplanes.

Common to the Ecuadorian coastal lowlands, a small tree frog called Scinax quinquefasciata, has been found with increasing frequency in Puerto Ayora, Isla Santa Cruz, since 1998. Seven individuals have been captured from three general areas within Puerto Ayora, the busiest port in the Galapagos.

Additional observations and captures have occurred in Villamil on Isla Isabela, and observations of an apparently similar frog have been made in Puerto Baquerizo Moreno on Isla San Cristobal. Over the last 20 years individual frogs of at least two other species have been sighted within the ports of Galapagos, but breeding populations were apparently never established.

The first observations of this species within Galapagos occurred during 1998 at the height of the 1997-1998 El Niņo event. Severe flooding occurred throughout the coastal regions of Ecuador and reports of unusually dense populations of frogs were common. Scientists are suggesting that once frogs arrived in the islands aboard ships or planes, the unusually wet conditions allowed establishment that has persisted due to the increased availability of suitable microhabitats associated with human habitation.

What happens when non-native amphibians enter the Galapagos eco-system? It is difficult to predict the potential impact of these frogs on the indigenous fauna of Galapagos. Frogs are mostly insectivorous so this species is presumably eating a variety of Galapagos insects and other invertebrates but scientists do not yet know the numbers or species being consumed. Many frogs have poison glands within their skin, and introduced frogs have caused striking declines in the populations of naive native predators in other parts of the world. Presently, scientists do not know if Scinax quinquefasciata possess such glands, nor if any Galapagos organisms are eating them.

But more research is expected. The current priorities concerning this newly introduced species aim to determine its distribution and rate of dispersal, compile information about potential means of eradication, search for breeding sites, and perform some simple experiments to explore the potential toxicity to indigenous predators.

Copyright 1999, Environmental News Network, All Rights Reserved

Note: Pages will open in a new browser window

External sites are not endorsed by CNN Interactive.