What is an Invasive Species?

What is an "invasive species"?

               An answer will depend whom you ask, and to a large extend what outcomes the person asked expects.

That was not a very helpful answer. Could you give a few answers that show different definitions of an "invasive species"?

               Sure.  First let's look at some words that are used to describe a change in species distribution that upset existing ecosystem balances and cause changes in ecosystem services that lead or may lead to system resource change or collapse:  adventive, alien, casual, colonizing, cryptogenic, escaped, endemic, established, exotic, foreign, immigrant, imported, introduced, invasive, native, naturalized, nonindigenous, noxious, nuisance, pest, spreading, temporary, tramp, transferred, transformer, transient, translocated, transplanted, transported, travelling, waif, and weedy. (Colautti & MacIsaac, 2004) Brendan Larson's thirteen meta categories to consider when we try to come to grips with a definition are: invaders, terrorists, piggy-backers, opportunists, spawn, mirrors of ourselves, providers, hybrids, tricksters, matrix elements and dynamic matrices, transients, founts of life and creation, teachers and instructors that force us to think about our assumptions. (Larson, 2007)   

Yes that is all very nice, but I want a simply straightforward definition.   

               Well, because of the complexities that arise from the ecosystems themselves and the many stakeholders and interested parties, there are many definitions. This happens because it is easier to start with an outcomes and work backwards to a definition. In other words we color the definition with preconceived ideas and concepts. This even our choice of words predisposes us to a view of the problem even before we have a definition. The very choice of the word invasive presumes a pejorative meaning, because natural system stakeholders so the negative impact of what to them looked like invasions.

Yeah Yeah Yeah, but I am just passing through and I do not have a lot of time for this, just give me a definition.

               The International Union for Conservation of Nature, (IUCN) describes invasive species as “animals, plants or other organisms introduced by man into places out of their natural range of distribution, where they become established and disperse, generating a negative impact on the local ecosystem and species.” Invasive species can negatively impact human health, the economy (i.e. tourism, agriculture), and native ecosystems. These impacts may disrupt the ecosystem processes, introduce diseases to humans or flora and fauna, and reduce biodiversity.

               Invasive Species Definition Clarification and Guidance White Paper Submitted by the definitions Subcommittee of the Invasive Species Advisory Committee (ISAC) in 2006 sought to make clear the US Executive Order 13112  which defines an invasive species as “an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.” In the Executive Summary of the National Invasive Species Management Plan (NISMP) the term invasive species is further clarified and defined as “a species that is non-native to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm or harm to human health.”   (Beck, et al., ISAC 2006)

               In California an invasive plant is defined by Cal-IPC as  invasive non-native plant species that threaten wildlands and are are not native to, yet can spread into, wildland ecosystems, and that also displace native species, hybridize with native species, alter biological communities, or alter ecosystem processes.   This definition does not address diseases, insects or animals, just plants and only if they invade California wildlands with native habitat values. The invasive plant definition does not include plant species found solely in areas of human-caused disturbance such as roadsides and cultivated agricultural fields.  For these human disturbance areas the terminology or word would be weed. The California Native Plant Society has a straight forward definition of an invasive exotic plant, to wit: "a plant which is able to proliferate and aggressively alter or displace indigenous biological communities."

               The European Commission on the Environment states that "Invasive Alien Species are animals and plants that are introduced accidently or deliberately into a natural environment where they are not normally found. They represent a serious threat to native plants and animals in Europe, causing € millions worth of damage every year."

Great now I need to understand what a native species is? I don't suppose there is a simple definition. is there?

               That would be a different blog posting. Definitions of native run into the same fuzzy definition problem  that we are skirting in this blog. The closer you look the harder it is to pin down exactly what the term means. What exactly is native at 650 ppm CO2 for example is a question no one is talking about. Suppose we move an endangered species to a new site; is it native now?

This invasive business requires too much thinking. Can't you make this simpler?

               Sure: an invasive species is the wrong pathogen, plant, animal in the wrong place at the wrong time.

Works Cited

Beck, K. G., Zimmerman, K., Schardt, J. D., Stone, J., Lukens, R. R., Reichard, S., et al. (ISAC 2006). Invasive Species Definition Clarification and Guidance White Paper. Retrieved March 2009, from http://www.invasivespeciesinfo.gov/docs/council/isacdef.pdf

Colautti, R. I., & MacIsaac, H. J. (2004). A neutral terminology to define ‘invasive’. Diversity Distrib. , 10, 135-141.

Larson, B. M. (2007). Thirteen ways of looking at invasive species. In D. R. Clements, & S. J. Darbyshire (Eds.), Invasive plants: Inventories, strategies and action. Topics in Canadian Weeds Science (Vol. 5). Canadian Weed Science Society – Société canadienne de.