Not all introduced are invasive
Many people believe the phrase “Introduced Species” is synonymous with “Invasive Species”. Below I’ve included the definitions of each of these terms:
“An introduced species (also known as an exotic species) is an organism that is not native to the place or area where it is considered introduced and instead has been accidentally or deliberately transported to the new location by human activity.” (science daily)
Invasive species is a phrase with several definitions:
- Invasive Species: non-indigenous species (e.g. plants or animals) that adversely effects the habitats they invade economically, environmentally or ecologically.
- Invasive Species: native and non-native species that heavily colonize a particular habitat.
- Invasive Species: a widespread non-indigenous species.
While the definition for an “Introduced species” may be clear, the term “Invasive Species” still struggles to come to a consensus definition. Though one definition sees invasive species as native or non-native species that heavily colonize a particular area, I will focus on the most common definition: that only exotic species have the potential to be invasive. As seen from the most accepted definitions, it is clear that all Invasive species are introduced species, but not all introduced species are invasive. If a species is not native to a region, it is considered “Introduced”. However, whether or not it receives the “Invasive” tag will depend on whether it exhibits adverse effects on its new environment. For example, the common goldfish (Carassius auratus) was introduced to the United States in 1850 and became extremely widespread, but has shown no adverse effects that characterize invasive species. Therefore, a goldfish would be an example of an introduced, but not invasive species. However, the third definition of “Invasive Species” does not link invasive species with adverse effects. So technically, their definition would include the common goldfish as an invasive species because it is non-native and is widespread. In the future, definition one needs to be made the unanimous definition for “Invasive Species” to avoid confusion and ambiguity in regard to the term.
How Invasive Species Spread
Many Invasive Species spread as a result of humans, and many times unintentionally. Below are some examples how they spread:
Ships: Ships can carry aquatic organisms. Currently there is a huge movement urging people to clean their boats in an attempt to avoid these unintentional introductions.
Wood products: Insects can get into wood, especially crates that are shipped from continent to continent.
Ornamental plants: Some ornamental plants can become invasive by escaping into the wild.
Pet trade: Some invasive species are intentionally or accidentally released pets. Burmese pythons are becoming a big problem in the Everglades.
(National Wildlife Federation)
Causes of Invasiveness
The Enemy release hypothesis argues that a non-native species can become invasive due to a lack of regulation from enemies in their new home. This allows species to increase in abundance and distribution (Keane & Crawley, 2002).
The Biotic Resistance Hypothesis states that species-rich communities use resources/nutrients more efficiently, allowing them to be more resistant to invasion than communities of low species-richness.
Another trait many invasive species show is their ability to overcome genetic bottlenecks. The bluespotted cornetfish are an example of a species that exhibited this trait. They went through a severe population bottleneck that decreased their genetic diversity to only two mitochondrial haplotypes. Even though this significant decline in genetic diversity is typically detrimental to an organism in a new environment, the bluspotted cornetfish had great success and spread rapidly.
Another important trait that allows and introduced species to become invasive is the ability to outcompete native species for resources. If the introduced organism was native and evolved in an area of high competition and predation, then the invader will have unique traits to allow it to grow and proliferate quickly in their new environment. These traits may allow them to outcompete the natives for nutrients, light, physical space, water, or food.
One reason the introduced species may have lacking competition is due to human induced disturbance in their new ecosystem. Due to the disturbance, the invaders are given a better chance to defeat the weakened natives.
If there is an Empty niche (role) in the ecosystem that has not been claimed by any species, the invasive may fill that role.
Adaption can also allow an invasive species to settle into a new environment and cause havoc. Novel genetic combinations or selective pressures can facilitate this adaption.
Ultimately, understanding the processes and causes of invasion is vital to secure global biodiversity. Onces the processes and causes are understodd, we will be able to combat them for the good of biodiversity everywhere. (Vitousek et al., 1997).
Effects of Invasion
“Biotic homogenization is the process by which species invasions and extinctions increase the genetic, taxonomic or functional similarity of two or more locations over a specified time interval. Biotic homogenization is now considered a distinct facet of the broader biodiversity crisis having significant ecological, evolutionary and social consequences” (Olden).
Beta diversity, which measures the differences in species found between regions, decreases both locally and regionally with the introduction of invasive species. This in turn decreases biodiversity (Wright).
Two examples of Worst Case Scenario Invasions in Missouri:
Introduced to North America in the late 1800s and 1900s, the bush honeysuckle is now known for problems it has caused in northern and central Missouri. Both Morrow’s and Amur honeysuckle have a broad tolerance for many different ecosystems of varying moisture levels. Disturbed habitats are especially vulnerable to their pesky plants. People suspect that they produce allelopathic chemicals that enter the soil and harm the growth of other plants. In addition, the shade created by bush honeysuckle may steal the sunlight from many native plants, especially because they grow their leaves before most plants and lose them after most plants. (Missouri Department of Conservation)
Asian Tiger Mosquito
Native to Southeast Asia, the Asian tiger mosquito, traveled to the United States in 1985 and reached St. Louis by 1986. The mosquitos originally arrived through a shipment of used tires from Japan and are thought to have traveled through the United States by human-aid. It is believed that they travel on car tires over highways across the United States. Their ability to spread combined with their ability to spread disease makes them extremely dangerous not only to their new ecosystems, but to humans around them. These aggressive daytime biters are suspected of spreading the chickunguna virus in the U.S. (Wustl)
Here is a printable version of the identification card.
“Invasive Species.” ScienceDaily. ScienceDaily, n.d. Web. 07 May 2015.
“Invasive Species – National Wildlife Federation.” Invasive Species – National Wildlife Federation. N.p., n.d. Web. 07 May 2015.
“The Enemy Release Hypothesis.” A Bugly Life. N.p., 31 Jan. 2013. Web. 07 May 2015.
Golani, Daniel, Ernesto Azzurro, Maria Corsini-Foka, Manuela Falautano, Franco Andaloro, and Giacomo Bernardi. “Genetic Bottlenecks and Successful Biological Invasions: The Case of a Recent Lessepsian Migrant.” Biology Letters. The Royal Society, n.d. Web. 07 May 2015.
“Biotic Homogenization.” Biotic Homogenization. N.p., n.d. Web. 07 May 2015.
Wright, Sarah. “Loss of Beta Diversity” Indiana University Press. 2011
“Bush Honeysuckles Control.” Bush Honeysuckles Control. N.p., n.d. Web. 07 May 2015.
Lutz, Diana. “Hot on the Trail of the Asian Tiger Mosquito | Newsroom | Washington University in St. Louis.” Hot on the Trail of the Asian Tiger Mosquito | Newsroom | Washington University in St. Louis. N.p., n.d. Web. 07 May 2015.