Guest blog by GCT volunteer- Camilla Oxley
An invasive species is any living organism that is not native to an ecosystem. They are found all around the world and are among the leading threats to indigenous wildlife. The introduction of invasive species interrupts the natural ecosystem and creates an imbalance in the biodiversity. They are particularly damaging to Galapagos as it is home to a large number of endemic species. Today there are an estimated 1,700 invasive species across the Galapagos Islands.
Invasive species are mainly introduced by humans either intentionally or unintentionally. International trade is one of the most common ways for non-native species to travel across the world. Some species such as cats, farm animals and plants have been purposely introduced to Galapagos for agricultural and domestic reasons. However, others such as rats, fire ants and Philorins downsi flies have been accidentally introduced possibly via cargo ships.
These species are responsible for modifying the food chain by outcompeting native species. When invasive species have an advantage, such as a lack of predators, they are able to reproduce and increase their populations rapidly. These aggressive species invasions cause an ecological disruption such as reducing the biodiversity of the ecosystem. Other threats include competition for essential resources such as food and territory, and also the contamination and dispersal of newly introduced diseases.
The fly, Philorins downsi is native to South America and was accidentally introduced to Galapagos in the 1950s. The flies have spread to 14 islands in the Archipelago and are a major threat to birds. The flies lay their eggs in the nasal cavities of the nestlings to feed on blood and tissue fluid. These flies cause multiple wounds and infections, eventually killing the nestlings. They have caused a massive threat to small populations of critically endangered birds such as the mangrove finch and the medium tree finch. These are just two of the 18 bird species in Galapagos that are affected.
The tropical fire ant (Solenopsis geminate) and the little fire ant (Wasmannia auropunctata) are known as the most efficient and widely distributed insect predators. They often attack in groups, killing small animals by biting and stinging them. They cause major threats to the endemic reptiles and birds. They are known to attack the eyes of the endangered Galapagos giant tortoises and eat the hatchlings. Not only that but they can cause serious reactions in humans too and disrupt agricultural activities.
The invasion of foreign plants poses a direct threat to the native vegetation of the Galapagos Islands. There are 500 known plants that are native, with 30% of them being endemic to the Islands. It is estimated that invasive plant species will soon outnumber the native plant species. The hill raspberry (Rubus niveus) for example, originates from the Himalayas and was introduced to the Galapagos Islands in 1970 for agricultural purposes. The seeds are dispersed over the islands by rats and birds that feed on the fruit.
The island of Floreana has been largely impacted by invasive species which has changed the landscape significantly. Currently, there are 55 species on Floreana that are listed on the IUCN Red List, including two critically endangered. 12 species are now locally extinct, but luckily surviving on nearby islands. This has mainly been due to the introduction of cats and rats, which prey on endemic species such as the Floreana mockingbird and the Galapagos racer.
GCT is supporting project partners to seek the complete eradication of all invasive mammals on Floreana. Once these have been removed, the locally extinct species can be re-introduced. This will bring the island back to its natural state and restore its biodiversity.
What can you do
Help us to restore Floreana to its former ecological glory by donating to our Restoring Floreana appeal or adopting a Floreana mockingbird. You can also provide ongoing support in Galapagos by becoming a GCT member.