Galapagos invasive species:
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Eradication – When to say Done?

In any programme of introduced species eradication one of the biggest problems is deciding exactly when you can finally announce to the world that the species has been successfully eradicated. The first individuals, be they plants, invertebrates or vertebrates, are relatively easy to find and eliminate as they are abundant and include all the most obvious, active or inquisitive individuals. However, the last are always the hardest as they are self-selected as being the most secretive, hidden or cautious. In many species, the presence of resting stages, diapause, hibernation or a seed bank, complicates the situation even more. The last individual is the most expensive of the entire programme, and if it is not found, the programme has failed.

bait sticks In a programme to eradicate the fire ant (Wasmannia auropunctata) from an area of ~21 ha on Marchena Island, we estimated that four years of fire ant-free monitoring were required to be sure of success. Due to the foraging behaviour of the target ants the methodology we used had to be intensive, with a minimum distance of 3-4 m between baits (sticks painted with peanut butter). At greater distances between baits the monitoring would have to be carried out for longer before the zone could be confidently declared fire ant-free. Moreover, monitoring should only take place during seasons of peak ant activity, that is, the rainy season. However, rain is infrequent, even in the wet season, and it can never be guaranteed that our team of 20 field workers will find favourable conditions on arrival at this distant island (11 hours by boat!). In 2005, no fire ants were found, marking three years of absence, but the results from this year are inconclusive, as the abundance of other species of invertebrates registered in a complementary monitoring programme were also low. Consequently, we decided to add one more year onto the monitoring programme.

introduced plant control In eradication projects of invasive plant and vertebrate species in Galapagos, a standard has been used of monitoring for two years following the last sighting of a live individual, whether adult, plant or seed. This implies a longer period of monitoring if it is known that there is a possibility that individuals could survive alive but undetected for longer, for example plant species with long-lived seeds in the ground.

The introduced plant “sauco macho” (Citharexylum gentryi) has been the focus of an eradication attempt for the last five years. We have succeeded in killing all the adults with the exception of less than five trees found with flowers or fruits in the last three years. Last year, 2004, we did not find a single adult. Despite this, we are finding many seedlings. The implication is that seeds live below the soil for three years, obviously essentially invisible until they germinate and produce seedlings. Making it even more difficult is the fact that the fruits are dispersed by birds, so a wide search (at least 400m) necessary around the known infestation.

With vertebrates the battle must include a consideration of their intelligence. A good example of this is the restoration of Baltra Island, which includes an eradication programme to eliminate the effect of feral cats in order to protect a population of land iguanas. In the last three monitoring trips, at the end of 2003, January 2004 and March 2005, no sign of cats or tracks were found – but if there are still individuals there, they must necessarily be those that don’t enter traps, take bait or which live in the most isolated and inaccessible places on the island.

When should the programme be terminated? That is the challenge, and depends much on the characteristics of the species.

Source: Charles Darwin Foundation and Galapagos National Park. June 2005.

Human activities have a negative impact on protected areas

Mine The demographic growth of the human population in Galapagos results in increasing pressure on the goods and services generated by the Galapagos National Park ecosystems. One example of this is shown by the results of an ecological evaluation carried out in 2002 by the Galapagos National Park Service, the body responsible for the administration and management of protected areas in Galapagos, in various Special Use Zone (SUZ) sites on Santa Cruz island: the Red Gravel mine which is a stone extraction site; the rubbish dump; and the peak of Crocker Hill where cell phone and VHF radio transmission antennas are sited.

As a general conclusion it could be seen that the presence of human activities within the protected area generated a big negative impact, due to the fact that each site within SUZ acted as a focal point for the arrival and dispersion of introduced species and, although the study was restricted to a single island, it is clear that the same pattern would be repeated in the other inhabited islands.

Yellow warbler in the rubbish dump In general, the flora, birds and crawling terrestrial invertebrates showed some signs of negative impact as a result of exposure to the use being made of each site. For example, the introduced bird the Ani, Crotophaga ani, was observed as frequently as native species of bird (shown in the photo), feeding on seeds and other waste in the rubbish dump. This has implications for the dispersion of seeds, especially of introduced plants, back into the area of origin of the native birds in the Primitive Zone of the National Park.rubbish dump Moreover, the altered habitats, whether by the creation of roads, paths or the removal of stone, were the sites of greatest abundance of introduced invasive plants, particularly the grass Pennisetum purpureum and the quinine tree Cinchona pubescens. Within the invertebrates, the displacement and decrease of populations of native and island endemic species was notable, principally due to the presence of two species of invasive ant, Wasmannia auropunctata and Solenopsis geminate.

Despite these results, the reality in the Galapagos archipelago is that the human population is growing, together with the number of researchers and resource managers; they must possess sufficient ability to take adequate management decisions which allow, in the long term, on the one hand rational use of the goods and services which can be exploited, and on the other guarantee the conservation of the ecological integrity and biodiversity of these fragile ecosystems.

Source: Galapagos National Park. March 2005.

Lessons of oceanic invasion: Galapagos-Hawaii case study summary

The archipelagos of Galapagos and Hawaii have many similarities, including their volcanic origin and relative size, but also many differences such as their age, history and the impact of humans. The Hawaiian Islands, for example, lie far from major continents and plants and animals have reached the islands only slowly. It is through this prolonged isolation that the outstandingly rich diversity of endemic plants and birds evolved.

sugar cane in nurseryThe Galapagos Islands are comparatively much younger, but closer to continental influences; consequently they have quickly developed a terrestrial fauna such as reptiles, rats and other invertebrate groups which are absent from Hawaii.

The Galapagos has lost less than 5% of its endemic biodiversity whereas Hawaii has more species extinctions per square area of land than anywhere else on the globe. Comparison of the history of both archipelagos and the subsequent impact of colonization by humans and attendant species, such as domestic livestock and rodents, crop plants, weeds and insects, is useful in analyzing the processes of change in these unique ecosystems.

Hawaii is now heavily populated and has large agricultural and tourism industries which serve as an indirect source of exotic species in the form of introduced pests, diseases and weeds. It also has direct sources of non-native species such as plant nurseries (as seen in the photo) and pet shops, creating greater risks for the introduction of new invasive species. In Galapagos, those responsible for its administration are working towards the implementation of adaptive management of the protected areas, using the precautionary principle.

However, a comparative case study is a useful means of identifying the best strategies for invasive species management both in Galapagos and Hawaii, as well as highlighting opportunities for learning from each others experience.

For further reading see the article "The challenge of effectively addressing the threat of invasive species to the National Park System" by Lloyd Loope.

Source: Charles Darwin Foundation and Galapagos National Park. December 2004.

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This website was created on 25 October 2004 by PT and JK.