The danger of invasive species
Part I: Animals
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In 1535 the Galapagos Islands were discovered. From that moment and with the onset of human activities, began its process of degradation, due in particular to the effect that introduced species had in an environment where indigenous species evolved without the presence of large predators.
The island ecosystems, lacking the selective pressures such as grazing by herbivores or the presence of predators, are highly vulnerable to biological invasions. Because of this, the mammals introduced to the islands in the last two centuries have had a highly successful colonization.
As human activity increased, the number of species of introduced animals also grew, for example, when the English scientist Charles Darwin visited the islands, he reported the presence of pigs (Sus scroffa) on Santiago Island.
The effects of introduced species are difficult to predict. In most cases, they can be detected only once they have been established, i.e., when it's too late to resolve the problem at its initial stage, this is when it tries to adapt to new living conditions and population numbers are low.
Source: Galapagos Report 2006-2007 (PDF, 5.4 MB)
In Galapagos, introductions can occur by sea or air. So the Inspection and Quarantine System for Galapagos (SICGAL) was implemented. The idea is to detect organisms before admission to the islands, through checks at the port of Guayaquil and in the airports of Quito, Guayaquil and Manta. Also, as a second barrier, luggage is checked of all passengers upon entering the airport in Galapagos and randomly for incoming cargo by ship and plane.
As a third barrier a strategy has developed for early detection of new introductions, through permanent monitoring in populated islands, where there is greater risk of introduction due to the constant movement of goods and services, which demands the development of productive activities. The objective of this activity is time to intercept the possible introduction of new species, especially invertebrates, which are more difficult to detect.
Thanks to this strategy, in 2008, in Puerto Ayora and Puerto Baquerizo Moreno, two new species of invertebrates were found: the Mediterranean fruit fly (Ceratitis capitata) and the big-headed ant (Pheidole megacephala). These two species were previously classified as species of potential risk to the islands, due to the effect that they caused at other sites of productive activities and on ecosystems similar to the Galapagos environment.
Impacts and extinctions
» The impact of goats in Galapagos
Without a sustained effort of constant monitoring and eradication, the impact of goats on the Galapagos ecosystem would be devastating.
Although there is no clear information, there is evidence that certain species of introduced animals have caused extinctions. For example, the black rat is the cause of the extinction of native rats on Santa Cruz Island, Baltra and San Cristobal. The same rat almost led to extinction the population of giant tortoises (G. ephippium) of Pinzón Island, because it impeded their natural reproduction.
Since the discovery of the islands, until now, there have been 36 species of vertebrates, of which 6 have been intercepted and 30 have established among which are: 13 mammals, 10 birds, 4 reptiles, 2 amphibians and one species of fish.
As for invertebrates, 543 species were recorded, of which it is estimated that 55 have the characteristics of causing severe impacts to the islands. This, based on a prioritization model that included an assessment of the possible ecological and economic impact that introduced insects can cause.
Although invasive species are considered the main threat to the unique flora and fauna of the Galapagos Islands, little is known about the impact the introduced invertebrates have on invertebrate populations of Galapagos.
The Bigheaded ant is a plague on other archipelagos, attacking newborn animals, like this chick on the Kure Atoll in Hawaii.
Not all of these species pose the same risk level for flora and fauna of the Galapagos. All have some effect, as predation or competition for food and living area. Moreover, many of these species serve as hosts or carriers of parasites and introduced diseases, which could have devastating effects on the fragile biodiversity of the islands.
An ongoing effort
The efforts that the Galapagos institutions have invested in actions involving monitoring, control or eradication have been enormous, in some cases concrete measures have been implemented to achieve eradication of one or more species, however, most resources are focused on actions to mitigate the effects that introduced organisms cause.
After having achieved eradication, the job is not done, continued monitoring activities are needed: a) to ensure that eradication has been successful and b) so that further reintroductions are detected in a timely manner.