What is an invasive species?

By Daniel Kuhl | A brief overview to introduced and invasive fauna

You have probably heard the term invasive animal, or introduced animal, especially if you’ve been in the Australian hunting community for any given amount of time. In this article I will do a brief overview of what an invasive species are, why they’re important to recognise, their pathways, and the sorts of damage they can do to the environment and different ecosystems.

An invasive species is an organism that is introduced to an environment through non-natural means and negatively impacts that new area¹. When an organism enters a new environment, one that has not evolved on conjunction with it, it has the ability to seriously offset the mutualistic balance that has not adapted to it. Due to this offset, the organisms in the affected area may not have appropriate defense mechanisms and as such can not protect themselves from a overpowered predator². Perhaps the invasive species is not a predator that affects another organism directly by killing it but could be out-competing other organisms for food or water resources, which leads the native organism to starve to death – and by extension, local area extinction.

So how do these organisms get to these new areas? Well, those are called transport vectors and pathways. A transport vector is the manner in which an organism moves along a pathway, with a pathway being the route between the original habitat and the new release location³. To give you a nice example of this, imagine a transport ship in the 1800’s. Here, we may have a deer loaded onto the ship in England, then traverse the ocean, and finally unloaded in Australia. In this instance, the ship is the vector and the path that the ship took is the pathway. This is important to know and understand, because it is through studying this we can identify and block these vectors and pathways.

This is relevant to Australia as we have many invasive species on this continent. This includes the Queensland fruit fly (Bacterocer tryoni)⁴, a native fruit fly from Northern Queensland that has spread through the continent damaging many millions of dollars of crops, the prickly pear (Opuntia focus-indica)⁵, the cactus-like plant which many people around Australia would be familiar with, and ranges to mammals such as the six various surviving deer species and pigs. All of these have been taken from their native range, and through some sort of transport vector and pathway, are in a new habitat and causing harm. Some of these will be explored in further write ups.

In summary, an invasive animal is an animal that has been introduced into a habitat it is not native to, through a vector and pathway, and (usually) has a negative effect on that area.

Lockwood, J.L., M.F. Hoopes, and M.P. Marchetti, Invasion ecology. 2nd ed. ed. 2013, Chichester, West Sussex, UK: Wiley-Blackwell.
Ehrenfeld, J.G., Ecosystem Consequences of Biological Invasions. Annual Review of Ecology, Evolution, and Systematics, 2010. 41: p. 59-80.
Mack, R.N. and W.M. Lonsdale, Humans as Global Plant Dispersers: Getting More Than We Bargained For. BioScience, 2001. 51(2): p. 95-102.
Clarke, A.R., et al., The ecology of Bactrocera tryoni (Diptera: Tephritidae): what do we know to assist pest management? Annals of Applied Biology, 2011. 158(1): p. 26-54.
Tesfay, Y.B. and J. Kreyling, The invasive Opuntia ficus-indica homogenizes native plant species compositions in the highlands of Eritrea. Biological Invasions, 2021. 23(2): p. 433-442.