“Invasive species” have become a well-known phenomenon, in part because of dangerous invasives like the Burmese Python (Python molurus) in the Everglades. But many people are hard-pressed to identify even the most conspicuous non-native species in their area. In South Florida, where I conduct my research on invasive anoles (lizards), most people I meet are surprised to learn that the Brown Anole (Anolis sagrei) –the most common lizard in the area – isn’t native, but an invasive species from Cuba.
But not every species that arrives in a new habitat is “invasive,” and a plethora of terms are used to describe species living outside their native range. Here are a few of the most common: invasive, exotic, non-native, non-indigenous, introduced, established, and naturalized. There are also more emotionally loaded terms like “weedy,” “nuisance,” and “noxious.” What’s the scientific consensus on these terms?
Exotic, non-native, and non-indigenous refer to species occurring outside their historical range. These species don’t necessarily have self-sustaining populations in their new range. Introduced has a similar meaning, but with the added twist of an anthropogenic (or human-caused) colonization event. Established and naturalized describe species that have reached stable, sustainable populations in their new range – they breed in sufficient numbers to perpetuate themselves.
Invasive is the trickiest term. Some people use it interchangeably with “exotic,” but this definition is too broad. Scientists tend to agree that the term invasive should be reserved for those species that have become established not only in human-altered habitats (like suburban neighborhoods), but also in natural habitats. Some also suggest that to be invasive, a species must have negative effects on native wildlife. Most exotic species, however, have not been studied carefully enough to determine whether they have negative impacts on native plants and animals.
In South Florida, exotic and invasive species are everywhere. The Brown Anole that I study is certainly an invasive by any definition – since becoming established in peninsular Florida in the 1940s, it has spread throughout the state and beyond. It occurs in all kinds of habitats, and it competes with the native green anole (A. carolinensis), which seems to be suffering from the interaction.
Other cases are less clear-cut. Red-masked parakeets (Aratinga erythrogenys), native to Ecuador and Peru, probably arrived in Miami through the pet trade. They have been established in Miami since the 1980s, and their populations seem to be self-sustaining if not growing. They haven’t spread into undisturbed habitats, however, and they don’t seem to be a threat to native species (although they may compete for nest holes with native cavity-nesting birds). So maybe we could call these parakeets “non-invasive exotics.”
Unfortunately, we just don’t know enough about most exotics to classify them as “invasive,” “potentially invasive,” or “non-invasive.” Since most exotics first become established in human-dominated habitats, we all have an important role to play in monitoring the arrival and spread of new species, as well as the interactions between these new arrivals and native species. So keep an eye on the wildlife in your neighborhood and see if you’ve got any new neighbors!
National Geographic Young Explorer Neil Losin is a biologist, photographer, and filmmaker pursuing his Ph.D. in UCLA’s Department of Ecology and Evolutionary Biology. Neil studies the evolution of territoriality in invasive Anolis lizards in South Florida