Terminology used for a new species in an area is diverse; Non-indigenous, alien, novel, invasive, or simply introduced (for example). What terms should we use? Can we eliminate some of these? What is the difference between a species expanding its range and a non-indigenous species being introduced into a new region? Taking much from Davis and Thompson (2000), certain criteria can be placed on these terms so use is consistent but I think these authors make it too complex and we can simplify the whole thing.
They (Davis and Thompson 2000) suggest three criteria, distance, uniqueness, and impact, to help classify species introductions/movement to a new area and their effects. But, as we will see, a species doesn’t need to to be new to an area to be placed into the invasivecategory.
Starting with the term invasive:
The term invasive should be applied to species that are expansive and detrimental to other species in the system, or the system itself, that is, that have an impact: Species that disrupt the working ecosystem (that is primarily the energy flow in the system). If a species, for example, whether its new to the region or not, takes over and dominates the systems, then its invasive. Cedar trees on the prairie show this typeof invasiveness. They are indigenous to the prairie but under some circumstances they take over whole area and prevent other species from thriving. The grassland is transformed into a m much different systems when cedars take over. Another example are the lionfish in the waters off Florida. Pacific Lionfish (Pteroissp.) are not indigenous to the Florida reef system. The lion fish out compete grouper, among other things, and they have a measurable impact on the reef systems that they are introduced to. In this case lionfish are both non-indigenous and invasive.
One problem: We can’t always determine that a species has disruptive impacts on a system. However, this then gives us a questions that we can…wait for it, do science on. Is the introduction of species Adetrimental to the system?” A worthy question that can be explored. Further questions, like “what is the specific impact?” And “how damaging to the system?”, (see categories below) can lead to further exploration.
Let us assume we have a novel species to the region. If it has moved from a directly adjacent region from its previously known area, it is a range extension for that species. If that species causes a large impact on the new communities into which it moves then that species would be considered invasive. The impact could then be categorized (1. moderate 2. major 3. massive) to signal the level of importance in dealing with the novel species. Non-indigenous species (NIS) classification would be maintained for novel species that have little measurable impact or whose impact has not been assessed. In this way I apply the term invasive species for organism that expand into new regions due to a changing climate if they also have a measurable impact. The impact could be to the community or economic.
Range expansion or new species to region:
Using the ideas again from Davis and Thompson (2000) and adding Blackburn et al.(2014). Distance is the key. The authors suggest that ‘short’ movement of a species equals range extension. I think we need to restrict this to directly adjacent movement to term species movement as a range extension. If a species moves from a directly adjacentregion into a new area then I would consider this movement a range extension. This species, however, could still be considered invasive based on its impact. So the level of impact, again, is the key reason to define a species as invasive.
Another thing tough to determine, and one used by Davis and Thompson (2000), is that a non-indigenous/“alien” species must be moved via human activities. This is even harder to determine with certainty than a species’ impact, and, though we can do science on it, the answer is less important than the impact, so I do not think we should restrict labeling something as a non-indigenous species to these criteria.
Another thing I do not like from Davis and Thompson (2000) is the idea of taxonomic uniqueness. They consider that for a species to be considered invasive it must meet at least two of the three criteria (distance, impact, and uniqueness). I do think uniqueness should be taken into account at all when categorizing a new species to an area. If a new crab species shows up on the New England coast, do we not categorize it as invasive because other crabs are present. If the species has a large impact that is enough to call it invasive.
Consequences of Invasive species on resident organisms:
Let’s look again at the Pacific Lionfishes (Pteroissp.). They are an invasive species (using the ideas above of course) in the Atlantic primarily in the coral reefs systems of the Caribbean (Schofield 2009). Lionfishes impact native species in a number of ways both direct and indirect. The most transparent impact is that of predation on smaller species and juvenile fishes (Green et al.2012). This direct effect includes impacts on commercial and sport fishes (Albins and Hixon 2008). There is also competition with other predators, the lionfishes compete with the Coney grouper for prey fishes (Albins 2013). Indirect effects of lionfishes are also predicted, for example with the loss of herbivorous reef fishes due to predation coral will hampered by excessive algae production (Albin and Hixon 2013).
There may be several things that aid in mediating the impact of lionfishes. Just as lionfishes compete with local predators in turn those predators haven’t lost the fight. Grouper presence seems to negatively influence lionfish presence (Mumby et al 2011) thus conveying a level of biotic resistance. The influence may be competitive but also might be direct predation. The effect, however, seems to be small in this direction—that is lionfishes effect grouper more than grouper effect lionfish. In this competitive game the lionfish seem to be winning.
Climate is a mediating factors for many invasive species. While this aspect may not have a positive affect along the southeast U.S. coast lionfishes are tropical species and the effects of colder winters will likely prevent them from taking hold in their furthest expansion north in North Carolina (Schofield 2009).
Population effects also mediate impacts. Most novel species go through a boom-bust cycle when first entering a new region. Populations grow quickly and reach the point where they outstrip the resources available. The population then crashes due to resource competition. This process has not yet been seen in lionfishes and due to the relatively slow growth of the invasive population, a first record within the Caribbean was 1986, they may not go through this process (Morris and Akins 2009).
There is much to study concerning species interactions and non-indigenous species, though they might have detrimental impacts, and thus be called invasive, this also gives us an opportunity to study the changes that occur in a system, which, in turn helps us understand how a systems functions.
Summary
The term invasive, should not be used for new species introduced into a region but instead reserved for species that have an impact (monetary or ecological) on the community into which they are introduced.
Range expansion
Only used if the species is known to move from a directly adjacentarea, otherwise we should use the term non-indigenous. The term non-indigenousshould be used rather than the term alien. Plus it allows us to use an acronym (NIS) and if you’ve read these blogs you know how I love those (sarcasm).
HOWEVER, if you are trying to get someone’s attention, aliensounds more threatening. So… do what you will.
Some readings- some cited above and some not
Albins MA. 2013 Effects of invasive Pacific red lionfish Pterois volitans versus a native predator on Bahamian coral reef communities. Biological Invasions. 15: 29-43.
Albins MA, and Hixon MA. 2013. Worst case scenario: potential log-term effects of invasive predatory lionfish (Pterois volitans) on Atlantic and Caribbean coral-reef communities.
Albins MA, and Hixon MA. 2008. Invasive Indo-Pacific lionfish Pterois volitans reduce recruitment of Atlantic coral-reef fishes. Marine Ecology Progress Series 367:233–238
Davis, M. and Thompson, K.: 2000, ‘Eight Ways to Be A Colonizer’, Bulletin of the
Ecological Society of America (July), 226–230.
Green SJ, Akins JL, Maljkovic ́ A, Cote ́IM. 2012. Invasive lionfish drive Atlantic coral reef fish declines. PLoS ONE 7(3):e32596
Morris Jr., J.A. and J. L. Akins. 2009. Feeding ecology of invasive lionfish (Pterois volitans) in the Bahamian archipelago. Environmental Biology of Fishes. 86(3): 389-398. doi: 10.1007/s10641-009-9538-8.
Mumby PJ, Harborne AR, Brumbaugh DR. 2011. Grouper as a natural biocontrol of invasive lionfish. PLoS ONE 6(6)
Schofield, P. J. 2009. Geographic Extent and Chronology of the Invasion of Non-Native Lionfish (Pterois Volitans and P. Miles) in the Western North Atlantic and Caribbean Sea. Aquatic Invasions. 4(3): 473-479.