Invasive Species: Just what exactly is an Invasive Species?

Invasive alien species are all organisms, animals, or plants that have a negative effect on “the local ecosystem and species” because humans have introduced them to an area that is outside of “their natural range,” and they then establish themselves and become broadly distributed in these areas. (Encyclopedia of Science and Technology Communication, 2010).

Cane toad (Bufo marinus) an extremely invasive pest species. Source: environment.gov.au. Assessed on the 13th of April 2014.

This basically means an introduced species is any organism that has been placed into an area that is not equip to sustain it without any negative effects of the native or original species of that area. These invasive species used up all the resources within the area, putting the native species at a disadvantage and eventually forcing them out of the area either by forcing them into extinction or causing them to move out of the area.
Invasive species generally have a higher rate of fecundity or in simpler terms, invasive species have a great rate of reproduction; producing more offspring than the native species and thus creating a population imbalance between the invasive species and the native ones.

The potential and actual distribution of the cane toad in Australia. Source: environment.gov.au. Assessed on the 13th of April 2014.

Most invasive species have either been intentionally or accidentally introduced into new areas by humans. Some invasive species were introduced into new areas in the hopes of decreasing the numbers of organisms that are affecting human livelihoods. An example of this is the  Cane Toad (Rhinella marina), the cane toad was released in small numbers around the cane farms located in Gordonvale, Queensland Australia. It was released in the hopes of controlling native grey-backed cane beetle (Dermolepida albohirtum) and French beetle (Lepidiota frenchi) (Clarke, G, et al 2000). This plan unfortunately backfired for the scientists involved, as the Cane Toads weren't all that interested in eating the beetles and could not jump high enough to reach the beetles located high up on the sugar cane. Instead the cane toads ate anything and everything else, with a high reproduction rate soon their populations skyrocketed out of control and spread throughout the rest of Cairns and soon throughout the rest of Queensland and beyond.

References:

• Clarke, G. M., Gross, S., Matthews, M., Catling, P. C., Baker, B., Hewitt, C. L., Crowther, D., & Saddler, S. R. 2000, Environmental Pest Species in Australia, Australia: State of the Environment, Second Technical Paper Series (Biodiversity), Department of the Environment and Heritage, Canberra.
• 2010. Encyclopedia of Science and Technology Communication. 1 Edition. SAGE Publications, Inc. Accessed on the 8th of March 2014.