DFW Invasive Species

Invasive Species 101

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Invasive Species 101

Non-native species, also referred to as alien, non-indigenous, foreign, or exotic, are plants, animals, or other organisms (such as microbes) that have been deliberately or unintentionally introduced to an area beyond their native range or from another site of introduction, usually by human actions (Kairo et al. 2003). Invasive species are those species (native or non-native) whose establishment causes economic damage, environmental harm to ecosystems, habitats, or species, or harm to human health (Presidential Executive Order 13112 Feb. 1999). Not all invasive species are non-native; native species can become invasive in response to an environmental change, such as habitat destruction or the removal of predator, and likewise, not all non-native species are invasive: these include livestock, agricultural, and ornamental species that confer benefit to human communities. This website focuses primarily on non-native invasive species that have become problematic to habitats and species within the USVI and are having negative environmental, economic, and cultural impacts.  

So, How Do They Get Here?

Almost all goods and raw materials used in the USVI have been imported via ship or air, providing ample opportunity for the movement of non-native organisms. While some problematic species have arrived in the U.S.V.I through colonization events such as natural range expansions (e.g., cattle egrets (Bulbicus ibis), although this species has expanded its range in response to widespread anthropogenic habitat change and animal husbandry practices (Arendt 1988)), most non-natives are the result of deliberate or accidental introduction by human mechanisms. 

Caribbean islands have a long history of species introductions. Early species of invaders include rats (Rattus spp.) transported on European ships, and sailors also introduced goats and other livestock to oceanic islands to ensure the availability of fresh meat on subsequent journeys. More recent unintentional introductions include Pacific Lionfish (Pterois spp.) presumably transported in ballast water of cargo ships, the Common Ground Lizard (Ameiva exsul) suspected to have been introduced to St. Croix in a tire shipment from Puerto Rico (Treglia et al. 2013), and Cuban Treefrogs (Osteopilus septentrionalis) and Puerto Rican Coquis (Eleutherodactylus coqui) as hitch-hikers in landscaping or construction material (Platenberg 2007).  

The Small Indian Mongoose (Herpestes auropunctatus) was deliberately released in an unsuccessful effort to control rats in agricultural fields (Nellis & Everard 1983). Cane Toads (Rhinella marina) were also released as a biocontrol for white grub (beetle larvae) agricultural pests. Both guinea grass (Megathyrsus maximus) and tan-tan (Leucaena leucocephala) were brought in as fodder for livestock. The presence of Red-eared Sliders (Trachemys scripta elegans) and Boa constrictors is the result of the pet trade: they were either intentionally released when owners were no longer willing or able to care for them, or escaped. The ornamental landscape trade has inadvertently introduced numerous invasive non-native species including: coral vine (Antigonon leptopus), rubber vine (Cryptostegia grandiflora), and sweet lime (Triphasia trifolia).  

While there is a good understanding of how organisms are arriving in the USVI, there is generally a poor understanding of the transport-enabling factors. These factors are species-specific, and are influenced by the behavior and biological requirements of these species. And while the scientific community is receptive to addressing the issue, the public may be resistant to the knowledge that common practices may have become a threat. 

What are the Impacts of Invasive Species?

Invasives are distinguished from other non-native species by their negative impact on native ecosystems. They may be predators of native species, compete with natives for limited resources, or introduce diseases to which the local population has not been exposed. They can also have significant economic impacts by infesting or invading human food systems, or otherwise affecting agriculture, fisheries, forestry, and tourism.