What is an invasive species?
This is a terrific question because many people get confused by the terms native, exotic, and invasive. A “native” species is one that naturally evolved or originated in a region without human intervention; also, one that occurs in an ecosystem for a reason other than human-aided introduction.
An “exotic” species references a species from a distant, foreign country. Also referred to as being “non-native” when found outside of its historical range and has been introduced accidentally or intentionally by humans.
“Invasive” describes an exotic or non-native species that, when introduced into an ecosystem, aggressively establishes itself at the expense of native plants or animals and causes, or is likely to cause economic or environmental harm or harm to human, animal, plant health.
“Invasive” is also colloquially applied to native species. The commonest examples of these species are “weeds”. For the purpose of management, these species are not formally designated as invasive and may be managed through different means.
Invasive species can cause damage that far outweighs their numbers. They can be mammals, birds, insects, reptiles, fish or shellfish, plants, viruses, fungi – any type of living organism. They can have major effects on natural habitats and native species. It can take many years between when an exotic species is introduced and when it becomes invasive, an interval referred to as lag time. Once an invasive species becomes abundant, it can be expensive and impossible to eradicate. It is illegal to introduce a species into Maryland’s ecosystems without first obtaining permits and performing careful risk assessments.
Are all non-native species invasive?
Most non-native or exotic species do not become invasive. Wheat, barley and rice are non-native, exotic species that were introduced but have not become invasive. Many aquatic species, such as goldfish and largemouth bass, have been introduced into Maryland without becoming invasive. Of all exotic species introduced, scientists estimated that 10% become established, and of those just 10% become invasive. That’s just 1 out of 100 species!
Unfortunately, it is not easy to predict which and when exotic species become invasive Well-known examples of invasive species, such as silver carp, purple loosestrife, and nutria resulted from intentional introductions of exotic species. Some exotic species may also introduce new pathogens that cause problems for other organisms including humans. It remains very difficult to predict whether an introduced exotic will become invasive. Because any exotic could become invasive or be detrimental to the ecosystem, the introduction of any species is a bad idea. In fact, in Maryland introductions now often require risk assessments and permits.
